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Perovskite precursor solution chemistry: From fundamentals to photovoltaic applications
Abstract
Over the last several years, inorganic-organic hybrid perovskites have shown dramatic achievements in photovoltaic performance and device stability. Despite the significant progress in photovoltaic application, an in-depth understanding of the fundamentals of precursor solution chemistry is still lacking. In this review, the fundamental background knowledge of nucleation and crystal growth processes in solution including the LaMer model and Ostwald ripening process is described. This review article also highlights the recent progress in precursor-coordinating molecule interaction in solution along with the role of anti-solvent in the solvent engineering process to control nucleation and crystal growth. Moreover, chemical pathways from precursor solution to perovskite film formation are given. This represents identification of the intermediate phase induced by precursor-coordinating molecule interaction and responsible intermediate species for uniform and dense perovskite film formation. Further to the description of chemical phenomena in solution, the contemporary progress in chemical precursor composition is also provided to comprehend the current research approaches to further enhance photovoltaic performance and device stability. On the basis of the critical and comprehensive review, we provide some perspectives to further achieve high-performance perovskite solar cells with long-term device stability through precisely controlled nucleation and crystal growth in precursor solution.
... This is a wet chemical synthesis approach that starts with precursor solutions or gels, which are then processed and dried to form a perovskite material [45]. It offers good control over composition and purity. ...
... The primary application of perovskite materials in biosensors is typically related to their luminescent or electronic properties. Here's how perovskite materials can be used in nanostructure biosensors: [45]. ...
... As shown in Fig. 1c, the GB density of Sb2S3 films decreases from 0.434 ± 0.027 μm cm -2 for the control sample to 0.319 ± 0.006, 0.303 ± 0.010, and 0.229 ± 0.006 μm cm -2 for the MEA-3, 7 MEA-4, and MEA-5 samples, respectively. The reduced GB density of the absorber films is expected to favor the suppression of non-radiative recombination 31 . The crosssectional SEM images (Fig. 1b) reveal that the Sb2S3 films shows a gradual increase of thickness with the addition of MEA. ...
Indoor photovoltaics (IPVs) have attracted increasing attention for sustainably powering Internet of Things (IoT) electronics. Sb$_2$S$_3$ is a promising IPV candidate material with a bandgap of ~1.75 eV, which is near the optimal value for indoor energy harvesting. However, the performance of Sb$_2$S$_3$ solar cells is limited by nonradiative recombination, closely associated with the poor-quality absorber films. Additive engineering is an effective strategy to improved the properties of solution-processed films. This work shows that the addition of monoethanolamine (MEA) into the precursor solution allows the nucleation and growth of Sb$_2$S$_3$ films to be controlled, enabling the deposition of high-quality Sb$_2$S$_3$ absorbers with reduced grain boundary density, optimized band positions and increased carrier concentration. Complemented with computations, it is revealed that the incorporation of MEA leads to a more efficient and energetically favorable deposition for enhanced heterogeneous nucleation on the substrate, which increases the grain size and accelerates the deposition rate of Sb$_2$S$_3$ films. Due to suppressed carrier recombination and improved charge-carrier transport in Sb$_2$S$_3$ absorber films, the MEA-modulated Sb$_2$S$_3$ solar cell yields a power conversion efficiency (PCE) of 7.22% under AM1.5G illumination, and an IPV PCE of 17.55% under 1000 lux white light emitting diode (WLED) illumination, which is the highest yet reported for Sb$_2$S$_3$ IPVs. Furthermore, we construct high performance large-area Sb$_2$S$_3$ IPV modules to power IoT wireless sensors, and realize the long-term continuous recording of environmental parameters under WLED illumination in an office. This work highlights the great prospect of Sb$_2$S$_3$ photovoltaics for indoor energy harvesting.
... Our investigation primarily focuses on comparing the physical and chemical properties of the nonvolatile (DMF/DMSO) and volatile (ACN) inks at first. Consistent with the classical LaMer model theory 40 41 . The resultant needle-like crystals remain pale gray color, suggesting non-photovoltaic phases. ...
Coupling mechanical and chemical effects during the crystal synthesis can lead to unexpected material attributes. The role of mechanical effects during the wet chemical synthesis of halide perovskite remains insufficiently explored, mainly due to its temporal asynchronization with the typical slower solvent evaporation-motivated chemical changes. In this study, we introduce mechanical shearing stress into a short temporal-window of crystal synthesis by using a fast-crystallization precursor system, which synergizes mechanical shearing effects with the atomic assembly thermodynamics of perovskite. This synthetic protocol facilitates cross-lengthscale influences, allowing macroscopic dynamic shearing to impact the atomic lattice rearrangement, growth, and facet orientation. Such an effect is consistently observed across atomic to inch-scale, culminating in films with long-range uniformity that are challenges via conventional methods. The as-synthesized perovskite films exhibit exceptional crystalline orientation and structural uniformity, demonstrating a significant Hermann’s orientation factor of -0.314 and leading to a remarkable power conversion efficiency of 25.90% on small area cell and exceeding 21% in a 70 cm ² solar module. This synthetic approach exemplifies the philosophy of utilizing mechanical shearing to foster the assembly of long-range ordered crystallographic lattice, thereby providing a new manufacturing route for synthesizing scalable high-quality perovskite films.
... To extract meaningful information from the PL decay curves and to understand the kinetics of the decay processes, we adopted a bi-exponential decay function [9,16,[45][46][47][48][49][50]. This mathematical representation is expressed as: ...
Current guidelines indicate that the lead levels in perovskite solar cells are sufficiently low, putting them on par with the safety of other lead-containing electronics. Yet, there remains ambiguity regarding the exact environmental impact of lead derived from perovskite. When this lead enters the soil, it has the potential to permeate plants and, subsequently, our food supply, at a rate that is a staggering ten times more than other lead contaminants from human-induced activities. Given this, it becomes vital to ensure that lead does not pollute our environment as we further adopt these technologies. In this study, we propose a novel method using polymer net bones to anchor the lead, which effectively reduces the risk of lead leaching due to rainfall. Perovskite Solar Cells (PSCs) integrated with this polymer net bone show improved operational efficiency and hold significant promise in curtailing lead leakage, reinforcing the ecological integrity of perovskite solutions. When enhanced with Polyvinyl Alcohol (PVA), these PSCs register a notable increase in Power Conversion Efficiency (PCE), scoring 24.7% as opposed to the 22.3% in PSCs devoid of PVA. Additionally, PVA-augmented PSCs outperform in stability when compared to their traditional counterparts.
... The great susceptibility of 1D chains to deformation sometimes results Hela in the emergence of desired features like piezo-and ferroelectricity, photochromism, or second-harmonic generation [16][17][18]. The production of crystals from a precursor solution is seriously influenced by the precursor composition and synthesis conditions [19][20][21], and the associated formation processes are poorly understood. However, the arrangement of octahedral units into 1D frameworks is strongly dependent on the presence of an organic cation in the system, especially its size, type (aromatic or aliphatic), and proton-donating or accepting abilities, which designate the intermolecular interactions and thus drive the crystal packing. ...
... Previous research has mainly focused on controlling the nucleation kinetics by ligand molecules 18,19 , low-temperature gradient 20 , or liquid diffusion 21 , which do not remarkably contribute to the following growth step. In essence, crystal growth is undoubtedly related to the mass transfer and surface reaction velocities, in which the slower one dominates the growth kinetics 22 . Concerning the fast surface condensation of monomers during crystal growth, mass transfer, as a ubiquitous process, has not yet been well understood, which is closely linked with the growth rate and defect formation of perovskite thin monocrystals 23 . ...
Metal-halide perovskite thin monocrystals featuring efficient carrier collection and transport capabilities are well suited for radiation detectors, yet their growth in a generic, well-controlled manner remains challenging. Here, we reveal that mass transfer is one major limiting factor during solution growth of perovskite thin monocrystals. A general approach is developed to overcome synthetic limitation by using a high solute flux system, in which mass diffusion coefficient is improved from 1.7×10–10 to 5.4×10–10 m² s–1 by suppressing monomer aggregation. The generality of this approach is validated by the synthesis of 29 types of perovskite thin monocrystals at 40–90 °C with the growth velocity up to 27.2 μm min–1. The as-grown perovskite monocrystals deliver a high X-ray sensitivity of 1.74×10⁵ µC Gy⁻¹ cm⁻² without applied bias. The findings regarding limited mass transfer and high-flux crystallization are crucial towards advancing the preparation and application of perovskite thin monocrystals.
... When the monomer concentration reaches the critical nucleation concentration (c min ), the colloids will undergo a burst nucleation. [60] Nucleation is terminated when the monomers concentration is lower than c min . Given the above-presented results, the perovskite colloidal particles with APDI 2 have a lower absolute zeta potential and thus a lower value of c min , ultimately driving up the nucleation rate and shortening the nucleation time. ...
Tin halide perovskites (THPs) have demonstrated exceptional potential for various applications owing to their low toxicity and excellent optoelectronic properties. However, the crystallization kinetics of THPs are less controllable than its lead counterpart because of the higher Lewis acidity of Sn²⁺, leading to THP films with poor morphology and rampant defects. Here, a colloidal zeta potential modulation approach is developed to improve the crystallization kinetics of THP films inspired by the classical Derjaguin‐Landau‐Verwey‐Overbeek (DLVO) theory. After adding 3‐aminopyrrolidine dihydro iodate (APDI2) in the precursor solution to change the zeta potential of the pristine colloids, the total interaction potential energy between colloidal particles with APDI2 could be controllably reduced, resulting in a higher coagulation probability and a lower critical nuclei concentration. In situ laser light scattering measurements confirmed the increased nucleation rate of the THP colloids with APDI2. The resulting film with APDI2 shows a pinhole‐free morphology with fewer defects, achieving an impressive efficiency of 15.13 %.
... The great susceptibility of 1D chains to deformation sometimes results Hela in the emergence of desired features like piezo-and ferroelectricity, photochromism, or second-harmonic generation [16][17][18]. The production of crystals from a precursor solution is seriously influenced by the precursor composition and synthesis conditions [19][20][21], and the associated formation processes are poorly understood. However, the arrangement of octahedral units into 1D frameworks is strongly dependent on the presence of an organic cation in the system, especially its size, type (aromatic or aliphatic), and proton-donating or accepting abilities, which designate the intermolecular interactions and thus drive the crystal packing. ...
In this paper, we report the synthesis and characterization of a new material, (HFlucytosine)2BiCl5. The structure studied
by single crystal X-ray diffraction reveals one-dimensional (1D) il [BiCl5]n
2− chains surrounded by protonated flucytosine
antifungal drug (HFlucytosine)+. The structure is stabilized by hydrogen bonds and non-covalent interactions. These
interactions were assessed using Hirshfeld surface analysis. The optical property of the compound was studied with a
focus on the band gap. Theoretical calculations on the electronic structure, band gap, and frontier molecular orbitals were
performed using density functional theory (DFT) and time-dependent DFT (TD-DFT) to support our experimental findings.
Our results indicate that the energy gap (Eg) and the chemical reactivity descriptors are primarily linked to the ring
of the organic cation and the inorganic anion. This highlights the importance of these two components in determining the
activity and antioxidant capacity of the molecule. To ascertain the efficacy of these compounds in inhibiting the proliferation
of detrimental bacteria, which are prevalent environmental contaminants in the Arab region, an agar disc diffusion
assay was performed.
... The great susceptibility of 1D chains to deformation sometimes results Hela in the emergence of desired features like piezo-and ferroelectricity, photochromism, or second-harmonic generation [16][17][18]. The production of crystals from a precursor solution is seriously influenced by the precursor composition and synthesis conditions [19][20][21], and the associated formation processes are poorly understood. However, the arrangement of octahedral units into 1D frameworks is strongly dependent on the presence of an organic cation in the system, especially its size, type (aromatic or aliphatic), and proton-donating or accepting abilities, which designate the intermolecular interactions and thus drive the crystal packing. ...
In this paper, we report the synthesis and characterization of a new material, (HFlucytosine)2BiCl5. The structure studied by single crystal X-ray diffraction reveals one-dimensional (1D) il [BiCl5]n²⁻ chains surrounded by protonated flucytosine antifungal drug (HFlucytosine)⁺. The structure is stabilized by hydrogen bonds and non-covalent interactions. These interactions were assessed using Hirshfeld surface analysis. The optical property of the compound was studied with a focus on the band gap. Theoretical calculations on the electronic structure, band gap, and frontier molecular orbitals were performed using density functional theory (DFT) and time-dependent DFT (TD-DFT) to support our experimental findings. Our results indicate that the energy gap (Eg) and the chemical reactivity descriptors are primarily linked to the ring of the organic cation and the inorganic anion. This highlights the importance of these two components in determining the activity and antioxidant capacity of the molecule. To ascertain the efficacy of these compounds in inhibiting the proliferation of detrimental bacteria, which are prevalent environmental contaminants in the Arab region, an agar disc diffusion assay was performed.
... Preheating the substrate also affects the degree of surface-induced nucleation as shown in Fig. 4e. Therefore, the morphology of the perovskite thin film can also be tuned by playing with the nucleation process of the perovskite crystals, which can be achieved by changing the temperature of the substrate or precursor solution during film fabrication; 146,162 however, this is not usually a common practice for Sn-based perovskites due to their nature of high Lewis acidity. Faster nucleation and slower crystal growth is an effective way to reduce defects in the Sn-PMs because a faster nucleation improves the extent of coverage of films, while the slower growth rate of perovskite crystals in a specific direction causes their orientation and high crystallinity as stated by the Wulff construction theory. ...
Perovskite solar cells (PSCs) hold promise in the photovoltaic market due to their unique opto electronic properties, ease of manufacture and excellent power conversion efficiency (PCE). Lead (Pb)-based perovskites, to this date, have the best PCE but face toxicity issues. Hence, Tin (Sn)-based perovskites are sought after as possible alternatives but struggle with low PCE due to stability and defect challenges. More still, Sn-based perovskite materials (Sn-PMs) have poor morphology and orientation due to their incomplete nucleation and fast crystal growth. To work around these issues for high performance Sn-PSCs, different important strategies have been reported in literature. Hence, this review starts with providing the reader with hints on the uniqueness of Sn-PMs in comparison to other Pb-free PMs. Then goes on to elaborate in detail the various strategies employed to improve Sn-PMs in PSCs mainly based on material crystallization thermodynamics and kinetics. Overall, the review provides an updated and systematic overview of various possible strategies that could improve Sn-PSCs. Keywords: Tin, perovskite, solar cells, Lead-free perovskites, stability, Tin oxidation.
... This is particularly important for light-emitting diodes (LEDs) with tunable emission wavelengths 16,17 , as well as tandem perovskite solar cells. However, MHPs with different compositions are significantly different in solubility, crystal nucleation kinetics, and trap characteristics [18][19][20][21] . For example, for organic-inorganic hybrid perovskites, such as formamidinium lead iodide (FAPbI 3 ), the inorganic component lead iodide (PbI 2 ) first precipitates out because of its much lower solubility (1.8 M) than formamidinium iodide (FAI) (9.2 M) in dimethylformamide at room temperature. ...
Presynthesized perovskite quantum dots are very promising for making films with different compositions, as they decouple crystallization and film-formation processes. However, fabricating large-area uniform films using perovskite quantum dots is still very challenging due to the complex fluidic dynamics of the solvents. Here, we report a robust film-formation approach using an environmental-friendly binary-solvent strategy. Nonbenzene solvents, n-octane and n-hexane, are mixed to manipulate the fluidic and evaporation dynamics of the perovskite quantum dot inks, resulting in balanced Marangoni flow, enhanced ink spreadability, and uniform solute-redistribution. We can therefore blade-coat large-area uniform perovskite films with different compositions using the same fabrication parameters. White and red perovskite light-emitting diodes incorporating blade-coated films exhibit a decent external quantum efficiency of 10.6% and 15.3% (0.04 cm²), and show a uniform emission up to 28 cm². This work represents a significant step toward the application of perovskite light-emitting diodes in flat panel solid-state lighting.
... Because the atoms bind more tightly to the substrate than to each other, the first condensed atom forms a complete monolayer on the surface, which is then covered by a second, less tightly bound layer. (3) Layer island, or Stranski-Krastanov growth model, after forming the first or several single molecular layers, islands are subsequently formed on top of the layer [47]. ...
In recent years, perovskite materials have garnered significant attention due to their exceptional light absorption performance, low exciton binding energy, and prolonged carrier lifetime. Among these materials, organic–inorganic hybrid perovskite solar cells (PSCs) have achieved an impressive photoelectric conversion efficiency (PCE) of 25.7%. However, the incorporation of organic cations has significantly compromised the wet and thermal stability of perovskite materials, thereby hindering their potential for commercialization. The utilization of all inorganic perovskites with Cs⁺ ions instead of organic ions has emerged as a promising approach that effectively circumvents such limitations. Notably, CsPbIBr2 perovskite exhibits an appropriate band gap and excellent environmental stability, making them a subject of broad academic interest. Nevertheless, the CsPbIBr2 film still faces challenges including inadequate film coverage, abundant defects, and suboptimal overall quality.The thermal engineering technique is employed to control the quality of the perovskite film in this study. Firstly, it enhanced the number of crystal nuclei by adjusting the preheating temperature of the FTO conductive substrate to significantly improve the coverage of the CsPbIBr2 film. Then, it modulate the growth of CsPbIBr2 crystal nuclei using a gradient annealing process. The specific practice is to preheat the substrate at a temperature of 60℃ for 10 min to spin coating into a film, and then annealing the prefabricated film at 100℃ for 1 min, then at 150℃ for 1 min, and finally at 250℃ for 10 min. The experimental results show that the surface of the CsPbIBr2 perovskite film is flat, compact and without pinholes, and the PCE of the assembled device is increased by 7.74%.
High-efficiency MPSCs with a PCE of 18.06% were prepared by introducing PACl to manipulate perovskite crystallization in a triple-mesoporous structure.
CsPbBr 3 @Cs 4 PbBr 6 hexagonal NCs with a bright photoluminescence (PL) peak of 456 nm are created through the dissolution‐recrystallization of CsPbBr 3 nanoplatelets. Small CsPbBr 3 nanocrystals are encapsulated in hexagonal Cs 4 PbBr 6 during recrystallization to form a core‐shell structure and keep high brightness and stability. The recrystallization kinetics is systematically investigated to explore the roles of methyl acetate, oleylamine, and n‐hexane. Result further indicates that core/shell NCs remained high PL under a variety of harsh conditions (e.g., light irradiation and heat treatment) because of Cs 4 PbX 6 shell and the controlling of recrystallization. Their initial PL intensity is remained after 4 months of storage under ambient conditions and continuous exposure to UV lamp for 180 min. The bright PL is also maintained even treatment at 120 °C. To indicate the universality of this synthesis method, CsPbX 3 @Cs 4 PbX 6 hexagonal NCs with different emission colors are fabricated by changing temperature, solvent viscosity, and precursors (e,g, oleylamine and halogens). These core‐shell samples reveal bright and stable green, orange, and red PL. Because of its high stability, the core/shell NCs are dispersed in flexible films to create diverse patterns. The films also exhibit high brightness and excellent stability. This strategy opens a novel avenue for the application of perovskite nanomaterials in the display field.
A heterogeneous seed-assisted FAPbI 3 crystallization facilitated by the 2,4-diaminopyrimidine (DAP) molecule, was employed to promotes the highly-crystalline α-FAPbI 3 film, significant increasing the efficiency of inverted device to 25.29%.
Antimony sulfide (Sb2S3) has attracted extensive attention due to its excellent photoelectric characteristics, including a high absorption coefficient (α > 10⁴ cm⁻¹) and a suitable bandgap (≈1.7 eV). However, due to its Q1D (quasi‐1D) structure, numerous deep‐level defects are identified in the Sb2S3 film, limiting the device's performance, and necessitating more efforts to overcome this situation. In this context, an ethanol solvent‐assisted chemical bath deposition (S‐CBD) strategy, a novel high‐quality thin film manufacturing technique is presented that modifies the supersaturation of the precursor solution by varying the boiling point and solvent polarity. This approach enables the effective regulation of the correlation between the crystal nucleation and growth rates, resulting in Sb2S3 films with large grains (≈4.25 µm, 37.5% ethanol), excellent crystallinity, well‐oriented structures (TC(211)/TC(020) = 2.39), low defect density, and prolonged carrier lifetimes (τAve ≈ 12.1 ns). Consequently, the final Sb2S3‐based solar device (FTO/CdS/Sb2S3/Spiro‐OMeTAD/Au) shows significant improvements in both FF (61.63%) and JSC (17.61 mA cm⁻²), yielding an excellent power conversion efficiency (PCE) of 7.84%. This research gives particular insights into the growth mechanism of high‐quality Sb2S3 thin films by CBD method as well as a potential route for enhancing Sb2S3 solar cell performance.
The non‐uniform distribution of colloidal particles in perovskite precursor results in an imbalanced response to the shear force during flexible printing process. Herein, it is observed that the continuous disordered migration occurring in perovskite inks significantly contributes to the enlargement of colloidal particles size and diminishes the crystallization activity of the inks. Therefore, a molecular encapsulation architecture by glycerol monostearate to mitigate colloidal particles collisions in the precursor ink, while simultaneously homogenizing the size distribution of perovskite colloids to minimize their diffusion disparities, is devised. The utilization of colloidal particles with a molecular encapsulation structure enables the achievement of uniform deposition during the printing process, thereby effectively balancing the crystallization rate and phase transition in the film and facilitating homogeneous crystallization of perovskite films. The large‐area flexible perovskite device (1.01 cm² and 100 cm²) fabricated through printing processes, achieves an efficiency of 24.45% and 15.87%, respectively, and manifests superior environmental stability, maintaining an initial efficiency of 91% after being stored in atmospheric ambiences for 150 days (unencapsulated). This work demonstrates that the dynamic evolution process of colloidal particles in both the precursor ink and printing process represents a crucial stride toward achieving uniform crystallization of perovskite films.
Perovskite solar cells (PSCs) exhibit sufficient technological efficiency and economic competitiveness. However, their poor stability and scalability are crucial factors limiting their rapid development. Therefore, achieving both high efficiency and good stability is an urgent challenge. In addition, the preparation methods for PSCs are currently limited to laboratory-scale methods, so their commercialization requires further research. Effective packaging technology is essential to protect the PSCs from degradation by external environmental factors and ensure their long-term stability. The industrialization of PSCs is also inseparable from the preparation technology of perovskite thin films. This review discusses the solvent-free preparation of PSCs, shedding light on the factors that affect PSC performance and strategies for performance enhancement. Furthermore, this review analyzes the existing simulation techniques that have contributed to a better understanding of the interfacial evolution of PSCs during the packaging process. Finally, the current challenges and possible solutions are highlighted, providing insights to facilitate the development of highly efficient and stable PSC modules to promote their widespread application.
Tin halide perovskite solar cells (PSCs) show promise as lead-free photovoltaic alternatives, but face challenges due to Sn2+ oxidation and crystallization control issues. We introduce a novel method to enhance...
Perovskite nanograins exceeding the Bohr exciton diameter show great potential for high‐performance light‐emitting diodes (LEDs) owing to their bandgap homogeneity, spatial charge confinement, and nonlocal interaction. However, it is challenging to directly synthesize proper nanograins along with reduced crystal defects on functional substrate, and the corresponding high‐efficiency perovskite LEDs (PeLEDs) have rarely been reported. In this study, crystallization modulation for perovskites with an effective co‐additive system, including lithium bromide, p‐fluorophenethylammonium bromide, and 18‐crown‐6, is performed. Furthermore, it is demonstrated that the proposed co‐additive system can synergistically retard perovskite crystallization and reduce crystal defects. Consequently, high‐quality perovskite nanograin solids (≈22.8 nm) are obtained with a high photoluminescence quantum yield (≈88%). These superior optical properties contribute to developing efficient green PeLEDs with a champion external quantum efficiency (EQE) of 28.4% and an average EQE of 27.1%. The co‐additive system can be universally applied to mixed‐halide perovskite nanograin LED, presenting a maximum EQE of 24.4%, 21.6%, 17.5%, and 11.1% for the blue device at 496, 488, 478, and 472 nm, respectively, along with a narrow spectral linewidth (17–14 nm) and stable color. These results supplement the research on high‐efficiency perovskite nanograin LEDs for multicolor displays and lighting.
While perovskite solar cells (PSCs) have exhibited an impressive power conversion efficiency (PCE) of 26.1%, their inherent instability poses a significant obstacle to their widespread commercialisation. Researchers worldwide have diligently employed diverse strategies to enhance their stability, ranging from configuration modifications to employing varied manufacturing techniques. This review meticulously explores the latest advancements in PSC devices, focusing primarily on the strategies employed to fortify stability, with an emphasis on configuration structures and fabrication methods. The study explores the critical stability parameters and considerations relevant to the long-term stability of PSC configurations. A comprehensive examination of the evolution of PSC configurations is presented, encompassing transitions from regular to inverted designs, the introduction of hole transport layer-free designs, the incorporation of electron transport layer-free configurations, and variations in the use of organic and inorganic materials. Moreover, the review compiles pertinent articles for additional reference, providing a consolidated resource for researchers and enthusiasts in the field. This review offers recommendations to improve the stability of hybrid PSCs and provides a perspective on supporting the commercialisation of PSC technology. Addressing the stability challenges outlined in this review is crucial for unlocking the full potential of PSCs and facilitating their seamless integration into the mainstream renewable energy landscape.
Maintaining the power conversion efficiency (PCE) of perovskite solar cells (PSCs) while enlarging the active area is necessary for their industrialization, where the key part is the uniform carrier extraction. Here, a conformal electron transport layer (ETL) is reported with eliminated low‐conductive contacts through a tailored deposition that combines chemical bath deposition and modified spin‐coating on a light‐managing textured substrate. The KPFM and C‐AFM are utilized to prove the uniform and optimized electrical properties. This study further employs the 2D measurements of PL and TRPL mapping to focus on revealing the enhanced uniformity of electron extraction. The uniform ETL conductivity and electron extraction contribute to a substantial decrease in device up‐scaling losses, making the δPCE (PCE0.08−PCE1PCE0.08)$\frac{{{\mathrm{PC}}{{{\mathrm{E}}}_{0.08}} - {\mathrm{PC}}{{{\mathrm{E}}}_1}}}{{{\mathrm{PC}}{{{\mathrm{E}}}_{0.08}}}})\ $ between 0.08 cm²‐device and 1 cm²‐device decrease from 5.02% to 2.97%, while the perovskite film is deposited using two‐step method. When using one‐step method to deposit perovskite film, PCEs of 25.13% and 23.93% for the active area of 0.08 cm² and 1 cm² are achieved, and the δPCE decreases from 7.89% to 4.77%, validating the significant effects on reducing up‐scaling losses. This work provides a new perspective to maintain high efficiency while device up‐scaling, providing more opportunities to push forward the PSCs industrialization.
Interfacial engineering of perovskite films has been the main strategies in improving the efficiency and stability of perovskite solar cells (PSCs). In this study, three new donor‐acceptor (D‐A)‐type interfacial dipole (DAID) molecules with hole‐transporting and different anchoring units are designed and employed in PSCs. The formation of interface dipoles by the DAID molecules on the perovskite film can efficiently modulate the energy level alignment, improve charge extraction, and reduce non‐radiative recombination. Among the three DAID molecules, TPA‐BAM with amide group exhibits the best chemical and optoelectrical properties, achieving a champion PCE of 25.29% with the enhanced open‐circuit voltage of 1.174 V and fill factor of 84.34%, due to the reduced defect density and improved interfacial hole extraction. Meanwhile, the operational stability of the unencapsulated device has been significantly improved. Our study provides a prospect for rationalized screening of interfacial dipole materials for efficient and stable PSCs.
Interfacial engineering of perovskite films has been the main strategies in improving the efficiency and stability of perovskite solar cells (PSCs). In this study, three new donor‐acceptor (D–A)‐type interfacial dipole (DAID) molecules with hole‐transporting and different anchoring units are designed and employed in PSCs. The formation of interface dipoles by the DAID molecules on the perovskite film can efficiently modulate the energy level alignment, improve charge extraction, and reduce non‐radiative recombination. Among the three DAID molecules, TPA‐BAM with amide group exhibits the best chemical and optoelectrical properties, achieving a champion PCE of 25.29 % with the enhanced open‐circuit voltage of 1.174 V and fill factor of 84.34 %, due to the reduced defect density and improved interfacial hole extraction. Meanwhile, the operational stability of the unencapsulated device has been significantly improved. Our study provides a prospect for rationalized screening of interfacial dipole materials for efficient and stable PSCs.
Halide perovskites show excellent optoelectronic properties for solar cell application. Notably, perovskite crystalline structures have been widely reported to deliver superior ferroelectric properties. As a result, the integration of the ferroelectric process with the photon‐to‐electron energy conversion process becomes feasible to generate interesting photo‐physical properties and further boost the device performance of perovskite solar cells (PSCs), which have started to attract more and more attention in recent years. Here, we have reviewed the recent progress in PSCs with ferroelectricity (FE‐PSCs), by classifying them into three regimes according to the degree of phase segregation, for example, the layer‐structured ferroelectric/halide perovskite composite, micro phase‐separated ferroelectric/halide perovskite composite, and the intrinsic ferroelectric halide perovskite composite. The different composite structures enable a large range of interesting optoelectronic properties and the specific structure significantly enhances the device performance of PSCs. The most prominent contribution of ferroelectricity is that it can provide an extra electrical field to drive charge generation, transport, and collection. Further, key challenges and opportunities of the integration of ferroelectricity with photovoltaics are discussed. We hope our work can draw intensive attention in this field to accelerate the establishment of the basic theories in ferroelectricity and the commercialization of PSCs.
Although perovskite solar cells (PSCs) have been developed rapidly, the poor quality of perovskite films and difficulty in scalable fabrication in air condition hindered the improvement of PSC performance. In...
Improving the crystallization quality of the perovskite film is crucial for both the efficiency and stability of perovskite solar cells. However, the solid-state transition of formamidinium lead iodide perovskite thin...
Tin halide perovskites (THPs) have demonstrated exceptional potential for various applications owing to their low toxicity and excellent optoelectronic properties. However, the crystallization kinetics of THPs are less controllable than its lead counterpart because of the higher Lewis acidity of Sn ²⁺ , leading to THP films with poor morphology and rampant defects. Here, a colloidal zeta potential modulation approach is developed to improve the crystallization kinetics of THP films inspired by the classical Derjaguin‐Landau‐Verwey‐Overbeek (DLVO) theory. After adding 3‐aminopyrrolidine dihydro iodate (APDI 2 ) in the precursor solution to change the zeta potential of the pristine colloids, the total interaction potential energy between colloidal particles with APDI 2 could be controllably reduced, resulting in a higher coagulation probability and a lower critical nuclei concentration. In situ laser light scattering measurements confirmed the increased nucleation rate of the THP colloids with APDI 2 . The resulting film with APDI 2 shows a pinhole‐free morphology with fewer defects, achieving an impressive efficiency of 15.13 %.
Ideal bandgap formamidinium tin-lead perovskite (FASn0.5Pb0.5I3) is appealing for fabricating thermally stable single-junction and tandem perovskite photovoltaics. Nevertheless, the obtain of high device efficiency is limited to the preparation of...
Formamidinium lead triiodide (FAPbI3) exhibits excellent thermal and chemical stability, making it a suitable alternative for methylammonium lead triiodide (MAPbI3) in high‐performance photodetectors. However, FAPbI3 faces the challenge of transforming from the metastable photoactive black phase α‐FAPbI3 to the photoinactive yellow phase δ‐FAPbI3 at room temperature. This phase transition is accelerated in humid atmospheric conditions. To realize high‐performance FAPbI3‐based photodetectors, it is crucial to form stable and highly crystalline phase‐pure α‐FAPbI3 films. Herein, is fabricate highly stable and crystalline FAPbI3 films and photodetectors through anti‐solvent additive engineering (AAE) using a green anti‐solvent (isopropanol, IPA) and an organic spacer (phenethylammonium iodide, PEAI). It is found that PEAI‐AAE treatment induced [001]‐preferred orientation growth in FAPbI3 films, and passivated defects within the crystal. The photodetectors based on PEAI‐AAE‐treated FAPbI3 film exhibits a fast response time of 485 µs/525 µs (rise time/fall time), high responsivity of 24.89 A W⁻¹, and excellent specific detectivity of 1.56 × 10¹³ Jones. Moreover, the PEAI‐AAE‐treated FAPbI3 photodetector retained over 80% of its initial performance even after exposure to ambient air for over 720 h, demonstrating excellent long‐term stability. This study provides a green processing method that paves the way for future commercialization of perovskite‐based optoelectronic devices.
Perovskite crystal growth regulation is a promising approach to obtaining high-quality perovskite films for boosting the application of corresponding of photovoltaic devices. However, complex nucleation paths frequently lead to low...
The escalating interest in low-dimensional perovskites stems from their tunable optoelectronic traits and robust stability. The pursuit of multifaceted optoelectronic devices holds substantial import for energy-efficient and space-constrained systems. This...
Despite the eminent performance of the organometallic halide perovskite solar cells (PSCs), the poor stability for humidity and ultraviolet irradiation is still major problem for the commercialization of PSCs. Herein, a novel functional organic compound 1‐(ammonium acetyl)pyrene is successfully introduced for preparing the 2D/3D heterostructured MAPbI3 perovskite. Because of the functional organic pyrene group with high humidity resistance and strong absorption in the ultraviolet region, the 2D/3D perovskite film shows notable stability with no degradation in ≈60% relative humidity after even six months and exhibits a high ultraviolet irradiation stability which keeps nearly no degradation after 1 h in the UV Ozone treatment. Planar PSCs are fabricated in the ≈60% relative humidity air outside glovebox. The champion efficiency of (PEY2PbI4)0.02MAPbI3 perovskite solar cells is 14.7% with nearly no hysteresis which is equal performance of 3D MAPbI3 devices (15.0%). This work presents a new direction for enhancing the solar cells' performance and stability by incorporating a functional organic aromatic compound into the perovskite layer. A novel organic compound 1‐(ammonium acetyl) pyrene is successfully introduced for preparing the 2D/3D heterostructured MAPbI3 perovskite. Because of the functional organic pyrene group with high humidity resistance and strong absorption in the ultraviolet region, the 2D/3D perovskite showed notable stability, comparable photovoltaic performance in humid air atmosphere and ultraviolet irradiation.
Perovskite solar cells (PSCs) require both high efficiency and good long-term stability if they are to be commercialized. It is crucial to finely optimize the energy level matching between the perovskites and hole-transporting materials to achieve better performance. Here, we synthesize a fluorene-terminated hole-transporting material with a fine-tuned energy level and a high glass transition temperature to ensure highly efficient and thermally stable PSCs. We use this material to fabricate photovoltaic devices with 23.2% efficiency (under reverse scanning) with a steady-state efficiency of 22.85% for small-area (~0.094 cm²) cells and 21.7% efficiency (under reverse scanning) for large-area (~1 cm²) cells. We also achieve certified efficiencies of 22.6% (small-area cells, ~0.094 cm²) and 20.9% (large-area, ~1 cm²). The resultant device shows better thermal stability than the device with spiro-OMeTAD, maintaining almost 95% of its initial performance for more than 500 h after thermal annealing at 60 °C.
The solution process is the most widely used method to prepare perovskite absorbers for high performance solar cells due to its ease for fabrication and low capital cost. However, an insufficient level of reproducibility of the solution process is often a concern. Complex precursor solution chemistry is likely one of the main reasons for the reproducibility issue. Here we report the effects of triple cation lead mixed-halide perovskite precursor solution aging on the quality of the resulting films and the device performance. Our study revealed that precursor solution aging has a great influence on the colloidal size distribution of the solution, which then affects the phase purity of the films and device performance. We determined the optimum aging hours that led to the best device efficiency along with the highest reproducibility. Dynamic light scattering revealed the formation of micron-sized colloidal intermediates in the solution when aged longer than the optimum hours and further analysis along with X-ray diffraction measurements suggested there were two chemical origins of the large aggregates, FA-based and Cs-based complexes.
3D organic–inorganic lead halide perovskites have shown great potential in efficient photovoltaic devices. However, the low stability of the 3D perovskite layer and random arrangement of the perovskite crystals hinder its commercialization road. Herein, a highly oriented 2D@3D ((AVA)2PbI4@MAPbI3) perovskite structure combining the advantages of both 2D and 3D perovskite is fabricated through an in situ route. The highest power conversion efficiency (PCE) of 18.0% is observed from a 2D@3D perovskite solar cell (PSC), and it also shows significantly enhanced device stability under both inert (90% of initial PCE for 32 d) and ambient conditions (72% of initial PCE for 20 d) without encapsulation. The high efficiency of 18.0% and nearly twofold improvement of device stability in ambient compared with pure 3D PSCs confirm that such 2D@3D perovskite structure is an effective strategy for high performance and increasing stability and thus will enable the timely commercialization of PSCs.
Methylammonium lead iodide perovskites hinder their practical applications due to a lack of the stability under operating conditions. The environmental stability under heat has not been achieved yet, although recent studies modifying perovskites with long organic cations reported the progress of the stability under humid conditions. In this work, we report structural evolution of long alkylammonium-modified MAPbI3 and their functions for highly efficient and stable solar cells. As a wrapping agent, octylammonium (OA) cation made individual MAPbI3 grains in full armour without the formation of layered structures in contrast to butylammonium (BA) and phenethylammonium (PEA) cations. Our OA-armoured MAPbI3 achieved a stabilised power conversion efficiency of 20.1% without a deterioration of charge transport properties due to highly preferential orientation suppressing non-radiative recombination. The structural features also led to much improved thermal stability at 85 °C in ambient atmosphere retaining 80% of initial efficiency after 760 h without any encapsulation as well as water tolerance. This work reconciles widespread concerns associated with photovoltaic efficiency and stability of MAPbI3 by exploring inter-relationship between structural features and their functions in surfactant-modified perovskites.
High‐efficiency perovskite solar cells are generally fabricated by using highly pure (>99.99 %) PbI2 mixed with an organic iodide in polar aprotic solvents. However, the use of such an expensive chemical may impede progress toward large‐scale industrial applications. Here, we report on the synthesis of perovskite powders by using inexpensive low‐grade (99 %) PbI2 and on the photovoltaic performance of perovskite solar cells prepared from a powder‐based single precursor. Pure APbI3 [A=methylammonium (MA) or formamidinium (FA)] perovskite powders were synthesized by treating low‐grade PbI2 with MAI or FAI in acetonitrile at ambient temperature. The structural phase purity was confirmed by X‐ray diffraction. The solar cell with a MAPbI3 film prepared from the synthesized perovskite powder demonstrated a power conversion efficiency (PCE) of 17.14 %, which is higher than the PCE of MAPbI3 films prepared by using both MAI and PbI2 as precursors (PCE=13.09 % for 99 % pure PbI2 and PCE=16.39 % for 99.9985 % pure PbI2). The synthesized powder showed better absorption and photoluminescence, which were responsible for the better photovoltaic performance. For the FAPbI3 powder, a solution with a yellow non‐perovskite δ‐FAPbI3 powder synthesized at room temperature was found to lead to a black perovskite film, whereas a solution with the black perovskite α‐FAPbI3 powder synthesized at 150 °C was not transformed into a black perovskite film. The α↔δ transition between the powder and film was assumed to correlate with the difference in the iodoplumbates in the powder‐dissolved solution. An average PCE of 17.21 % along with a smaller hysteresis [ΔPCE=PCEreverse−PCEforward)=1.53 %] was demonstrated from the perovskite solar cell prepared by using δ‐FAPbI3 powder; this PCE is higher than the average PCE of 17.05 % with a larger hysteresis (ΔPCE=2.71 %) for a device based on a conventional precursor solution dissolving MAI with high‐purity PbI2. The smaller hysteresis was indicative of fewer defects in the resulting FAPbI3 film prepared by using the δ‐FAPbI3 powder. Done dirt cheap: Pure APbI3 [A=methylammonium (MA) or formamidinium (FA)] perovskite powders are synthesized by treating low‐grade PbI2 with MAI or FAI in MeCN at ambient temperature. The solar cell with a MAPbI3 film prepared from the synthesized powder shows higher power conversion efficiency (17.14 %) than solar cells with MAPbI3 films prepared by using both MAI and 99 % (13.09 %) or 99.9985 % (16.39 %) pure PbI2 as precursors.
High-efficiency perovskite solar cells (PSCs) need to be fabricated in the nitrogen-filled glovebox by the atmosphere-controlled crystallization process. However, the use of the glovebox process is of great concern for mass level production of PSCs. In this work, notable efficient CH3NH3PbI3 solar cells can be obtained in high humidity ambient atmosphere (60-70% relative humidity) by using acetate as the antisolvent, in which dependence of methyl, ethyl, propyl, and butyl acetate on the crystal growth mechanism is discussed. It is explored that acetate screens the sensitive perovskite intermediate phases from water molecules during perovskite film formation and annealing. It is revealed that relatively high vapor pressure and high water solubility of methyl acetate (MA) leads to the formation of highly dense and pinhole free perovskite films guiding to the best power conversion efficiency (PCE) of 16.3% with a reduced hysteresis. The devices prepared using MA showed remarkable shelf life stability of more than 80% for 360 h in ambient air condition, when compared to the devices fabricated using other antisolvents with low vapor pressure and low water solubility. Moreover, the PCE was still kept at 15.6% even though 2 vol % deionized water was added in the MA for preparing the perovskite layer.
The efficiencies of perovskite solar cells (PSCs) are now reaching such consistently high levels that scalable manufacturing at low cost is becoming critical. However, this remains challenging due to the expensive hole-transporting materials usually employed, and difficulties associated with the scalable deposition of other functional layers. By simplifying the device architecture, hole-transport-layer-free PSCs with improved photovoltaic performance are fabricated via a scalable doctor-blading process. Molecular doping of halide perovskite films improved the conductivity of the films and their electronic contact with the conductive substrate, resulting in a reduced series resistance. It facilitates the extraction of photoexcited holes from perovskite directly to the conductive substrate. The bladed hole-transport-layer-free PSCs showed a stabilized power conversion efficiency above 20.0%. This work represents a significant step towards the scalable, cost-effective manufacturing of PSCs with both high performance and simple fabrication processes.
The effects of adding NH4Cl via an air blow process on CH3NH3PbI3(Cl) perovskite solar cells were investigated. CH3NH3PbI3(Cl) solar cells containing various amounts of NH4Cl were fabricated by spin-coating. The microstructures of the resulting cells were investigated by X-ray diffraction, optical microscopy, and scanning electron microscopy. The current density–voltage characteristics of the cell were improved by adding an appropriate amount of NH4Cl and air blowing, which increased the photoconversion efficiency to 14%. Microstructure analysis indicated that the perovskite layer contained dense grains with strong (100) orientation, as a result of NH4Cl addition and air blowing. The ratio of the (100)/(210) reflection intensities for the perovskite crystals was 2000 times higher than that of randomly oriented grains. The devices were stable when stored in ambient air for two weeks.
2D halide perovskites have recently been recognized as a promising avenue in perovskite solar cells (PSCs) in terms of encouraging stability and defect passivation effect. However, the efficiency (less than 15%) of ultrastable 2D Ruddlesden–Popper PSCs still lag far behind their traditional 3D perovskite counterparts. Here, a rationally designed 2D-3D perovskite stacking-layered architecture by in situ growing 2D PEA2PbI4 capping layers on top of 3D perovskite film, which drastically improves the stability of PSCs without compromising their high performance, is reported. Such a 2D perovskite capping layer induces larger Fermi-level splitting in the 2D-3D perovskite film under light illumination, resulting in an enhanced open-circuit voltage (Voc) and thus a higher efficiency of 18.51% in the 2D-3D PSCs. Time-resolved photoluminescence decay measurements indicate the facilitated hole extraction in the 2D-3D stacking-layered perovskite films, which is ascribed to the optimized energy band alignment and reduced nonradiative recombination at the subgap states. Benefiting from the high moisture resistivity as well as suppressed ion migration of the 2D perovskite, the 2D-3D PSCs show significantly improved long-term stability, retaining nearly 90% of the initial power conversion efficiency after 1000 h exposure in the ambient conditions with a high relative humidity level of 60 ± 10%.
Perovskite solar cells (PSCs) are promising alternatives toward clean energy because of their high-power conversion efficiency (PCE) and low materials and processing cost. However, their poor stability under operation is still limiting practical applications. Here we design an innovative approach to control the surface growth of a low dimensional perovskite layer on top of a bulk three-dimensional (3D) perovskite film. This results in a structured perovskite interface where a distinct layered low dimensional perovskite is engineered on top of the 3D. Structural and optical properties of the stack are investigated and solar cells realized. When embodying the low dimensional perovskite layer, the photovoltaic cells exhibit an enhanced PCE of 20.1% on average, when compared to pristine 3D perovskite. In addition, superior stability is observed: the devices retain 85% of the initial PCE stressed under one sun illumination for 800 hours at 50°C in ambient environment.
Solution-processed metal-halide perovskites have demonstrated immense potential in photovoltaic applications. Inkjet printing is a facile scalable approach to fabricate large-area perovskite solar cells (PSCs) due to its cost-effectiveness and near unity material utilization ratio. However, controlling crystallinity of the perovskite during the inkjet printing remains a challenge. The PSCs deposited by inkjet printing typically have much lower power conversion efficiencies (PCEs) than those by spin-coating. Here, we show that high-quality perovskite films could be inkjet-printed with an innovative vacuum-assisted thermal annealing post-treatment and optimized solvent composition. High-performance PSCs based on printed CH3NH3PbI3 with a PCE of 17.04% for 0.04 cm² (13.27% for 4.0 cm²) and negligible hysteresis (lower than 1.0%) are demonstrated. These efficiencies are much higher than the previously reported ones using inkjet-printing (≤12.3% for 0.04 cm²). The inkjet printing combined with vacuum-assisted thermal annealing could be an effective low-cost approach to fabricate high-performance perovskite optoelectronic thin film devices (including solar cells, lasers, photodetectors, and light-emitting diodes) with high-volume production.
Perovskite solar cells (PSCs) have great potentials in photovoltaics due to their high power conversion efficiency and low processing cost. PSCs are usually fabricated from PbI2/dimethylformamide solution with some toxic additives, such as N-methyl pyrrolidone and hexamethylphosphoramide. Here, we use an environmental friendly aprotic polar solvent, 1,3-dimethyl-2-imidazolidinone (DMI), to fabricate perovskite films. By adding 10 vol% DMI in the precursor solution, high-quality perovskite films with smooth surface are obtained. By increasing annealing temperature from 100 to 130 °C, the average grain size of the perovskite increases from ~ 216 to 375 nm. As a result, the efficiency of the PSCs increases from 10.72 to 14.54%.
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High crystallinity and compactness of the active layer is essential for metal-halide perovskite solar cells. Here, a simple pseudohalide-induced film retreatment technology is developed as the passivation for preformed perovskite film. It is found that the retreatment process yields a controllable decomposition-to-recrystallization evolution of the perovskite film. Corresponding, it remarkably enlarges the grain size of the film in all directions, as well as improving the crystallinity and hindering the trap density. Meanwhile, owing to an intermediate catalytic effect of the pseudohalide compound (NH4SCN), no crystal orientation changing and no impurity introduction in the modified film. By integrating the modified perovskite film into the planar heterojunction solar cells, a champion power conversion efficiency of 19.44% with a stabilized output efficiency of 19.02% under 1 sun illumination is obtained, exhibiting a negligible current density–voltage hysteresis. Moreover, such a facile and low-temperature film retreatment approach guarantees the application in flexible devices, showing a best power conversion efficiency of 17.04%.
Perovskite photovoltaics have attracted remarkable attention recently due to their exceptional power conversion efficiencies (PCE). State-of-the-art perovskite absorbers typically require thermal annealing steps for high film quality. However, the annealing process adds cost and reduces yield for device fabrication and may also hinder application in tandem photovoltaics and flexible/ultra-low-cost optoelectronics. Herein, we report an additive-based room-temperature process for realizing high-quality methylammonium lead iodide films with micron-sized grains (>2 μm) and microsecond-range carrier lifetimes (τ1= 931.94 ± 89.43 ns; τ2 = 320.41 ± 43.69 ns). Solar cells employing such films demonstrate 18.22% PCE with improved current-voltage hysteresis and stability without encapsulation. Further, we reveal that room-temperature-processed perovskite film grain size strongly depends on the precursor aggregate size in the film-deposition solution and that additive-based tuning of aggregate properties enables enlarging grains to the micron scale. These results offer a new pathway for more versatile, cost-effective perovskite processing.
Perovskite solar cells are remarkably efficient; however, they are prone to degradation in water, oxygen and ultraviolet light. Cation engineering in 3D perovskite absorbers has led to reduced degradation. Alternatively, 2D Ruddlesden–Popper layered perovskites exhibit improved stability, but have not delivered efficient solar cells so far. Here, we introduce n-butylammonium cations into a mixed-cation lead mixed-halide FA0.83Cs0.17Pb(IyBr1−y)3 3D perovskite. We observe the formation of 2D perovskite platelets, interspersed between highly orientated 3D perovskite grains, which suppress non-radiative charge recombination. We investigate the relationship between thin-film composition, crystal alignment and device performance. Solar cells with an optimal butylammonium content exhibit average stabilized power conversion efficiency of 17.5 ± 1.3% with a 1.61-eV-bandgap perovskite and 15.8 ± 0.8% with a 1.72-eV-bandgap perovskite. The stability under simulated sunlight is also enhanced. Cells sustain 80% of their ‘post burn-in’ efficiency after 1,000 h in air, and close to 4,000 h when encapsulated.
Organic–inorganic hybrid halide perovskite solar cells (PSCs) have recently drawn enormous attentions due to their impressive performance (>22%) and low temperature solution processability (<150 °C). Current solution process involves application of a large amount of toxic solvents, such as chlorobenzene, which is heavily employed in both the perovskite layer and the hole transport layer (HTL) deposition. Herein, this study employs green solvent of ethyl acetate for engineering efficient perovskite and HTL layers, which enables a synergic interface (perovskite/HTL) optimization. A champion efficiency of 19.43% is obtained for small cells (0.16 cm2 with mask) and over 14% for large size modules (5 × 5 cm2). The PSCs prepared from the green solvent engineering demonstrate superior performance on both efficiency and stability over their chlorobenzene counterparts. These enhancements are ascribed to the in situ inhibition on carrier recombination induced by interfacial defects during the solution processing, which enables about 2/3 reduction of calculated recombination rate. Thus, the green solvent route shows the great potential toward environmental-friendly manufacturing.
Solar-to-electricity conversion efficiency (PCE) and stability are two important aspects of perovskite solar cells. However, both aspects are difficult to simultaneously enhance. In recent two years, 2D/3D stacking structure, designed by covering the 3D perovskite with a thin 2D perovskite capping layer, was reported to be a promising method to achieve both a higher PCE and improved stability simultaneously. However, when reducing the surface defects of 3D perovskite, the thin 2D capping layer itself may probably introduce additional interfacial defects in a 2D/3D stacking structure, which is thought to be able to trigger trap-assisted non-radiative recombination or ion migration. Thus, efforts should be paid to reduce the interfacial defects of 2D hybrid perovskite when serving as modification layer in a 2D/3D stacking structure PSCs. Here, we demonstrate that bromine (Br) doping of the 2D perovskite capping layer is an efficient strategy to passivate interfacial defects robustly, by which the photoluminescence lifetime is enhanced notably while the interfacial charge recombination is suppressed a lot. As a result, the PCE is enhanced from 18.01% (3D perovskite) to 20.07% (Br doped 2D/3D perovskite) along with improved moisture stability.
Perovskite solar cells based on an all printable mesoporous stack, made of overlapping titania, zirconia, and carbon layers, represent a promising device architecture for both simple, low‐cost manufacture, and outstanding stability. Here a breakthrough in the upscaling of this technology is reported: Screen printed modules on A4 sized conductive glass substrates, delivering power conversion efficiency (PCE) ranging from 3 to 5% at 1 sun on an unprecedented 198 cm² active area. An increase in the PCE, due to higher VOC and fill factor, is demonstrated by patterning the TiO2 blocking layer. Furthermore, an unexpected increase of the performance is observed over time, while storing the modules in the dark, unencapsulated, at ambient conditions (with humidity increasing from 30 and 70% RH), resulting in 6.6% PCE and 6.3% stabilised at Vmax measured after over two months since fabrication. Equally impressive is the low light performance with 11 and 18% PCE achieved respectively at 200 and 1000 lux under fluorescent lighting. It is hoped that this demonstration of good performance on large area can unlock the viability of perovskite solar cells manufactured on an industrial scale.
Perovskite based photovoltaic devices hold the promise to greatly reduce the cost of solar energy production; however, this potential depends greatly on the ability to deposit perovskite active layers using large scale depositon methods such as slot-die coating without sacrificing efficiency. Using a prerovskite precursor ink with long wet-film processing window, we demonstrate efficient perovskite solar cells based on slot-die coated perovskite layer. We found almost no difference in the photophysical and structural details of perovskite films that were deposited by spin coating to films deposited by slot-die coating. We explored various slot-die coating parameters to determine their effect on the performance of the device metrics. In addition to slot-die coating, we demonstrate the versitility of this wide wet-film processing window by fabricating perovskite solar cells with active layers deposited by spin coating, blade coating, and spray coating that all exhibited similar performance.
Chemical origin of solvents typically used for preparation of hybrid lead halide perovskites – dimethyl sulfoxide (DMSO), dimethylformamide (DMF) and gamma-butyrolactone (GBL) – strongly influences on the process of perovskite crystallization due to formation of intermediate adducts with different structures and morphology. The composition and crystal structures of the adducts depend on the coordination and binding ability of the solvents and the ratio of the precursors. New adducts of perovskite and GBL either with an unusual cluster structure, (MA)8(GBL)x[Pb18I44], or an adduct (MA)2(GBL)2Pb3I8 similar to those observed for DMF and DMSO are described for the first time. Complex equilibriums between chemical species existing in perovskite solutions is revealed by Raman spectroscopy. As a result, new features of the perovskite crystallization through intermediate adduct phases are discussed and effective perovskite deposition pathways are suggested.
We investigate the impact of excess PbI2 in the precursor solution on the structural and optical properties of thin films of the model hybrid perovskite methylammonium lead iodide (MAPbI3). We find that excess of PbI2 in the precursor solution results in crystalline PbI2 in the final thin film that is located at the grain boundaries. From UPS we find that this crystalline PbI2 phase has no direct impact on the electronic structure of MAPbI3. In contrast to that, temperature dependent absorption measurements indicate a systematic change in the temperature dependence of the exciton binding energy in the perovskite. We also observe a decrease in the critical temperature and a concomitant smearing out of the tetragonal – orthorhombic phase transition as a function of excess PbI2. Our results thus help to better understand the exact role of PbI2 in the perovskite layer and pave the way for a more tailored design of perovskite solar cell.
Layered perovskites with the formula (R-NH3)2PbI4 have excellent environmental stability but poor photovoltaic function due to the preferential orientation of the semiconducting layer parallel to the substrate and the typically insulating nature of the R-NH3+ cation. Here, we report a series of these n = 1 layered perovskites with the form (aromatic- O-linker-NH3)2PbI4 where the aromatic moiety is naphthalene, pyrene, or perylene and the linker is ethyl, propyl, or butyl. These materials achieve enhanced conductivity perpendicular to the inorganic layers due to better energy level matching between the inorganic layers and organic galleries. The enhanced conductivity and visible absorption of these materials led to a champion power conversion efficiency of 1.38%, which is the highest value reported for any n = 1 layered perovskite, and it is an order of magnitude higher efficiency than any other n = 1 layered perovskite oriented with layers parallel to the substrate. These findings demonstrate the importance of leveraging the electronic character of the organic cation to improve optoelectronic properties and thus the photovoltaic performance of these chemically stable low n layered perovskites.
Organic-inorganic CH 3 NH 3 PbI 3 (MAPbI 3) inverted structured perovskite films were prepared using Pb (CH 3 COO) 2 (Pb(OAc) 2) and CH 3 NH 3 I (MAI) as source materials. The structural, optical and photoelectronic properties of the MAPbI 3 films varied with the Pb(OAc) 2 /MAI molar ratio. It was found that the Pb(OAc) 2 /MAI molar ratio greatly influenced the structure and morphology of the MAPbI 3 films. A suitable amount of excessive Pb(OAc) 2 (about 5 mol% excessive Pb) in the solution made the film smoother with improved film crystallinity. This resulted in enhanced power conversion efficiency (PCE). However, for films derived from solution with low Pb(OAc) 2 /MAI or high Pb(OAc) 2 /MAI ratio, defects such as pits or pinholes were easily formed with low crystallinity, and hence decreased the lifetime of the carriers and photoelectrical properties of the final solar cells. Using a solution with 5% excessive Pb, inverted structured CH 3 NH 3 PbI 3 perovskite solar cells with PCE of nearly 14% were obtained.
The Lewis acid-base adduct approach has been widely used to form uniform perovskite films, which has provided a methodological base for the development of high-performance perovskite solar cells. However, its incompatibility with formamidinium (FA)-based perovskites has impeded further enhancement of photovoltaic performance and stability. Here, we report an efficient and reproducible method to fabricate highly uniform FAPbI3 films via the adduct approach. Replacement of the typical Lewis base dimethyl sulfoxide (DMSO) with N-methyl-2-pyrrolidone (NMP) enabled the formation of a stable intermediate adduct phase, which can be converted into a uniform and pinhole-free FAPbI3 film. Infrared and computational analyses revealed a stronger interaction between NMP with the FA cation than DMSO, which facilitates the formation of a stable FAI•PbI2•NMP adduct. Based on the molecular interactions with different Lewis bases we proposed criteria for selecting the Lewis bases. Owed to the high film quality, perovskite solar cells with the highest PCE over 20% (stabilized PCE of 19.34%) and average PCE of 18.83±0.73% were demonstrated.
All current highest efficiency perovskite solar cells (PSCs) use highly toxic, halogenated solvents, such as chlorobenzene (CB) or toluene (TLN), in an antisolvent step or as solvent for the hole transporter material (HTM). A more environmentally friendly antisolvent is highly desirable for decreasing chronic health risk. Here, the efficacy of anisole (ANS), as a greener antisolvent for highest efficiency PSCs, is investigated. The fabrication inside and outside of the glovebox showing high power conversion efficiencies of 19.9% and 15.5%, respectively. Importantly, a fully nonhalogenated solvent system is demonstrated where ANS is used as both the antisolvent and the solvent for the HTM. With this, state‐of‐the‐art efficiencies close to 20.5%, the highest to date without using toxic CB or TLN, are reached. Through scanning electron microscopy, UV–vis, photoluminescence, and X‐ray diffraction, it is shown that ANS results in similar mixed‐ion perovskite films under glovebox atmosphere as CB and TLN. This underlines that ANS is indeed a viable green solvent system for PSCs and should urgently be adopted by labs and companies to avoid systematic health risks for researchers and employees.
Organic–inorganic hybrid lead halide perovskites are emerging as highly promising candidates for highly efficient thin film photovoltaics due to their excellent optoelectronic properties and low‐temperature process capability. However, the long‐term stability in ambient air still is a key issue limiting their further practical applications. Herein, the enhancement of both performance and stability of perovskite solar cells is reported by employing 2D and 3D heterostructured perovskite films with unique nanoplate/nanocrystalline morphology. The 2D/3D heterostructured perovskites combine advantages of the high‐performance lead‐based perovskite 3D CH3NH3PbI3 (MAPbI3) and the air‐stable bismuth‐based quasi‐perovskite 2D MA3Bi2I9. In the 2D/3D heterostructure, the hydrophobic MA3Bi2I9 platelets vertically situate between the MAPbI3 grains, forming a lattice‐like structure to tightly enclose the 3D MAPbI3 perovskite grains. The solar cell based on the optimal 2D/3D (9.2%) heterostructured film achieves a high efficiency of 18.97%, with remarkably reduced hysteresis and significantly improved stability. The work demonstrates that construction of 2D/3D heterostructured films by hybridizing different species of perovskite materials is a feasible way to simultaneously enhance both efficiency and stability of perovskite solar cells.
An antisolvent (iodobenzene, IB) was used to assist the formation of closely packed CH3NH3PbI3 (MAPbI3) thin films during the one-step spin-coating process using different volumes of IB. The morphological, structural, optical and excitonic properties of MAPbI3 thin films were analyzed using a contact-mode atomic-force microscope, X-ray diffractometer, broadband absorbance spectrometer and optical microscope-based time-resolved photoluminescence spectrometer. The properties of the resultant MAPbI3 thin films can be manipulated by using different IB volumes, which dominates the device performance of MAPbI3 based photovoltaic cells. The experimental results show that the grain size (or particle size) of MAPbI3 thin films influences the collection of photoexcited carriers and the contact at the 6,6-Phenyl C61 butyric acid methyl ester (PCBM)/MAPbI3 interface, thereby resulting in a trade-off between the fill factor (FF) and short-circuit current density (JSC). In addition, it is predicted that the power conversion efficiency (PCE) can be further improved by increasing the crystallinity of the MAPbI3 thin film while keeping the small grain size.
Thermal degradation in perovskite solar cells is still an unsettled issue that limits its further development. In this study, 2-(1H-pyrazol-1-yl)pyridine is introduced into lead halide 3D perovskites, which allows 1D–3D hybrid perovskite materials to be obtained. The heterostructural 1D–3D perovskites are proved to be capable of remarkably prolonging the photoluminescence decay lifetime and suppressing charge carrier recombination in comparison to conventional 3D perovskites. The intrinsic properties of thermodynamically stable yet kinetically labile 1D materials allow the system to alleviate the lattice mismatch and passivate the interface traps of heterojunction region of 1D–3D hybrid perovskites that may occur during the crystal growth process. Importantly, the as-fabricated 1D–3D perovskite solar cells display a thermodynamic self-healing ability, which is induced through blocking the ion-migration channels of A-site ions by the flexible 1D perovskite with less densely close-packed structure. Particularly, the power conversion efficiency of as-fabricated unencapsulated 1D–3D perovskite solar cells is demonstrated to be reversible under temperature cycling (25–85 °C) at 55% relative humidity, which largely outperforms the pure 3D perovskite solar cell. The present study provides a facile approach to fabricate 1D–3D perovskite solar cells with high efficiency and long-term stability.
CH3NH3PbI3-based planar perovskite solar cells were fabricated by slot-die coating, a scalable method. Slot-die coating tends to produce perovskite layers with much lower coverage with overgrown crystals than spin coating, which does not include a self-drying mechanism in the process. To mimic the self-drying behavior inherent in spin coating, the present study introduces a blowing step in the slot-die coating method, which significantly improved coverage of the prepared slot-die coated perovskite films. The slot-die-coated device with blowing showed a moderate power conversion efficiency (PCE) of 8.8%. The morphology of the slot-die-coated perovskite film is further improved by optimizing the deposition temperature. The combination of blowing and heating during the slot-die-coating step and the introduction of a printing-friendly hole transport layer resulted in a PCE of 12.7% for the devices fabricated in air.
It has been reported that incorporating hydrophobic large cations into three dimensional (3D) perovskite can improve moisture stability. In this work, we report the benefits of grain boundary passivation when a small amount of phenethylammonium cation (PEA+) is incorporated into (HC(NH2)2PbI3)0.85(CH3NH3PbBr3)0.15 perovskite for the first time. After adding small amounts of PEA cation (< 10%), perovskite film morphology is changed but most importantly grain boundaries are passivated. This is supported by Kelvin Probe Force Microscopy (KPFM). The passivation results in the increase in photoluminescence intensity and carrier lifetimes of test structures and open circuit voltages (VOC) of the devices as long as the addition of PEA+ is ≤4.5%. The formation of the higher bandgap the quasi-2D PEA incorporated perovskite is responsible for the grain boundary passivation. In addition, this quasi-2D material also resides TiO2 layer revealed by PL spectroscopy. Results of moisture exposure tests show that PEA+ incorporation is effective in slowing down the degradation of un-encapsulated devices compared to the control devices without PEA+. These findings provide insights into the operation of perovskite solar cells when large cations are incorporated and pathways for further stability improvement.
The rapid improvement in power conversion efficiencies (PCE) to record high levels have highlighted perovskite solar cells’ great potential to be commercialized in the near future. Continuous roll-to-roll (R2R) processing on flexible substrates enables ultra low-cost and high throughput manufacturing, which is essential for perovskite solar cells to make a breakthrough in cost per Watt compared to commercially established solar cells technologies. Here we demonstrate a facile spin-coating-free and R2R compatible blowing-assisted drop-casting (BADC) method to prepare CH3NH3PbI3 films for perovskite solar cells. The crystallinity and morphology of CH3NH3PbI3 films and device performance are significantly improved by optimization of the formulation with an NH4Cl additive. The perovskite solar cell prepared in air with a maximum PCE of 19.48% is obtained using modified poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (m-PEDOT:PSS) as the hole transport layer (HTL). The cells based on the structure of ITO/m-PEDOT:PSS/CH3NH3PbI3/PCBM/Ca/Al exhibit negligible current hysteresis. The optimized formulation is then successfully applied to slot-die coating on glass and subsequently to R2R on a flexible substrate, giving record PCEs of 15.57% and 11.16%, respectively.
An efficient CH3NH3PbI3 perovskite solar cell (PSC) whose performance is reproducible and shows reduced dependence on the processing conditions is fabricated using the cyclic urea compound 1,3-dimethyl-2-imidazolidinone (DMI) as an additive to the precursor solution of CH3NH3PbI3. X-ray diffraction analysis reveals that DMI weakly coordinates with PbI2 and forms a CH3NH3PbI3 film (Film-DMI) with no intermediate phase. The surface of annealed Film-DMI (Film-DMI-A) was smooth, with an average crystal size of 1 μm. Photoluminescence and transient photovoltage measurements show that Film-DMI-A exhibits a longer carrier lifetime than a CH3NH3PbI3 film prepared using the strongly coordinating additive DMSO (Film-DMSO-A), because of the reduced number of defect sites in Film-DMI-A. A solar cell based on Film-DMI-A exhibits a higher power conversion efficiency (17.6%) than that of a cell based on Film-DMSO-A (15.8%). Furthermore, the performance of the Film-DMI-A solar cell is less sensitive to the ratio between PbI2 and DMI, and Film-DMI can be fabricated under a high relative humidity of 55%.
Generally, residual solvent is embedded in perovskite precursor films fabricated from the
Lewis adduct method. Most of research focus on the ligand function of the solvent in forming
solvate complex for fabricating high quality perovskite films. But, few attentions are paid to the
latent function of the solvent in the perovskite precursor films during annealing process due to its
fast extravasation at high temperature. Here, we develop a sandwich configuration of
substrate/perovskite precursor films/PC61BM to retard the extravasation of solvent during
annealing. We find that the restrained solvent induces an obvious solvent-mediated dissolution-recrystallization process, leading to high quality perovskite films with large columnar grains.
There are mass transportation from small grains to large grains in the dissolution-recrystallization
process, which follows the Ostwald ripening model. Inverted planar solar cells are fabricated
basing on this annealing method. The photovoltaic performance of the solar cells are improved
significantly due to its high quality perovskite films with large columnar grains.
All-inorganic CsPbBrI2 perovskite has great advantages in terms of ambient phase stability and suitable band gap (1.91 eV) for photovoltaic applications. However, the typically used structure causes reduced device performance, primarily due to the large recombination at the interface between the perovskite, and the hole-extraction layer (HEL). In this paper, an efficient CsPbBrI2 perovskite solar cell (PSC) with a dimensionally graded heterojunction is reported, in which the CsPbBrI2 material is distributed within bulk–nanosheet–quantum dots or 3D–2D–0D dimension-profiled interface structure so that the energy alignment is optimized in between the valence and conduction bands of both CsPbBrI2 and the HEL layers. Specifically, the valence-/conduction-band edge is leveraged to bend with synergistic advantages: the graded combination enhances the hole extraction and conduction efficiency with effectively decreased recombination loss during the hole-transfer process, leading to an enhanced built-in electric field, hence a high VOC of as much as 1.19 V. The profiled structure induces continuously upshifted energy levels, resulting in a higher JSC of as much as 12.93 mA cm−2 and fill factor as high as 80.5%, and therefore record power conversion efficiency (PCE) of 12.39%. As far as it is known, this is the highest PCE for CsPbBrI2 perovskite-based PSC.
Anti-solvent assisted crystallization (ASAC) is currently one of the most widely used methods to obtain perovskite films with great quality due to its advantage of low cost and easy operation. The commonly used anti-solvents, toluene, and chlorobenzene (CB), are well recognized to be contaminants in drinking water and exhibit high toxicity levels. It is desirable to develop environmentally benign solvents for the fabrication of perovskite solar cells by ASAC method. As a green solvent, methoxybenzene (PhOMe) has the advantages of low toxicity, moderate saturated vapor pressure, and similar solvent features with toluene and CB. Here, we report highly efficient planar perovskite solar cells (PSCs) prepared by ASAC method using PhOMe green anti-solvent, achieving a power conversion efficiency (PCE) of 19.42%, which is better than CB processed PSCs (19.09%). Compared to CB processed perovskite films, perovskites produced by PhOMe exhibit smoother surfaces, larger grains, and lower carrier recombination rates, while the crystallization and absorption features remain basically unchanged. These results demonstrate that PhOMe is an excellent anti-solvent alternative for high-quality perovskites and thus provide new opportunities for environmental-friendly manufacturing of PSCs and other optoelectronic devices.
One of the attractive features of hybrid perovskite is the possibility to reduce its dimensionality, which enhance the perovskite’s resistivity to moisture. In this work we used 2D/3D perovskites for studying different organic molecular spacers (aromatic ring vs. cyclic ring); Cs was introduced as an additional small cation to methylammonium. It was found that Cs improves the photovoltaic performance; however, it reduces the cells’ stability because two cations having a different ionic radius are mixed, which creates strains in the perovskite structure. The aromatic ring spacers display better stability in complete cells than does the cyclo spacer. Importantly, Cs has a greater effect on the stability than does the nature of the spacer molecule. The difference in the size of the organic cations as well as the inorganic cations plays a major role in the perovskite’s stability in a film and in a complete solar cell.
With the aid of formic acid, CH3NH3PbI3 single crystal of 9 mm in length was directly harvested within 3 days via a nonseeded solution temperature-lowering (STL) method. It showed a record-narrow full width at half maximum of 13 arcsec for the high-resolution X-ray rocking curve, a low trap-state density of 3.1 × 10⁹ cm⁻³, a high carrier mobility of 162 cm² V⁻¹ s⁻¹ and high moisture stability. The addition of formic acid could suppress the oxidation of iodide ions in a conventional STL process, resulting in rapid growth of high-quality CH3NH3PbI3 single crystals.
We have fabricated planar heterojunction perovskite solar cells by one-step ultrasonic spray-coating of the perovskite precursor solution in air. Uniform perovskite films with high surface coverage can be prepared after optimization of the precursor solution and spray-coating parameters. We found that the purity of PbI2, although varying only from 98 to 99.9%, can significantly affect the crystallinity, grain size and boundaries of MAPbI3 that were fabricated via one-step spray-coating, and ultimately determined the power conversion efficiency (PCE) of devices. PbI2 with a purity of 98% resulted in a low conversion of precursors to perovskite, whilst a high purity of 99.9% led to perovskite with high crystallinity, large grain size and narrow grain boundaries. Our p-i-n type, planar heterojunction solar cell ITO/PEDOT:PSS/MAPbI3/PCBM/Ag made from MAI and the 99.9% purity PbI2 achieved a maximum PCE of 12.6% without hysteresis, whereas the 98% purity PbI2-based device showed a low PCE of 4.9% only with the presence of hysteresis. However, the impacts of PbI2 purity on device efficiency can be minimized by changing the deposition method from one-step spray-coating to a two-step spin casting approach.
We report a systematic investigation on the role of excess PbI2 content on CH3NH3PbI3 perovskite film properties, solar cell parameters and device storage stability. We used the CH3NH3I vapor assisted method for the preparation of PbI2-free CH3NH3PbI3 films under N2 atmosphere. These pristine CH3NH3PbI3 films were annealed at 165 °C for different time intervals in N2 atmosphere to generate additional PbI2 in these films. From XRD measurements, the excess of PbI2 were quantified. Detailed characterizations including scanning electron microscopy, X-ray diffraction, UV-Visible and photoluminescence for continuous aging of CH3NH3PbI3 films in ambient condition (50 % humidity) are carried out for understanding the influence of different PbI2 content on degradation of the CH3NH3PbI3 films. We find that the rate of degradation of CH3NH3PbI3 is accelerated due to the amount of PbI2 present in the film. A comparison of solar cell parameters of devices prepared using CH3NH3PbI3 samples having different PbI2 content reveals strong influence on the current density-voltage hysteresis as well as storage stability. We demonstrate that CH3NH3PbI3 devices do not require any residual PbI2 for high performance. Moreover, a small amount of excess PbI2, which improves the initial performance of the devices slightly, has undesirable effects on the CH3NH3PbI3 film stability as well as on device hysteresis and stability.
Organic-inorganic lead halide perovskite has become one of the most attractive materials for future low-cost high-efficiency solar technology. However, the polycrystalline nature of perovskite thin-film often possesses an exceptional density of defects, especially at grain boundaries (GBs) and film surface, limiting further improvement in the power conversion efficiency (PCE) of the perovskite device. Here, we report a simple method to reduce GBs and to passivate the surface of a methylammonium lead tri-iodide (MAPbI3) film by guanidinium thiocyanate (GUTS)-assisted Ostwald ripening post treatment. High-optoelectronic quality MAPbI3 film consisting of micron-sized grains were synthesized by post-treating a MAPbI3 film with GUTS/isopropanol solution (4 mg/mL, GUTS-4). Analysis of the electrochemical impedance spectra (EIS) of the solar cells showed that interfacial charge recombination resistance of the device based on a GUTS-4 post-treated MAPbI3 absorber film was increased by a factor of 1.15–2.6, depending on light illumination intensity, compared to the control MAPbI3 cell. This is consistent with results of the open-circuit voltage (Voc) decay and the light intensity dependent photovoltage evolution which shows device with GUTS treatment had one order longer charge carrier lifetime and was more ideal (ideality factor = 1.25). Further characterization by Kelvin probe force microscope indicated that GUTS-4 treatment shifted the energetics of the MAPbI3 film by ~ 100 meV towards better energy level alignment with adjacent SnO2 electron transport layer, leading to a more favorable charge extraction process at the MAPbI3/SnO2 interface. As a result, the PCE of PSCs was enhanced from 14.59% to 16.37% and the hysteresis effect was mitigated.
The deposition of dense and uniform perovskite films with large grains is crucial for fabricating high-performance perovskite solar cells (PSCs). High-quality CH3NH3PbI3 films were produced by a self-induced intragranular-coarsening approach. The perovskite precursor solution contained a Lewis base, N,N-dimethyl sulfoxide (DMSO), and was deposited using a gas-assisted, one-step, spin-coating method that was followed by a solvent vapor-assisted annealing treatment using a mix of DMSO and chlorobenzene (CBZ). Combining solvent-engineering with gas-assisted deposition helps to form intermediate crystalline entities upon evaporation of the parent solvent but retards the otherwise fast reaction between the precursor ingredients. Subsequent cosolvent annealing induces further grain-coarsening via a facilitated dissolution-precipitation process. This technique produced flat CH3NH3PbI3 films featuring large grain microstructures, with well-coarsened subgrains and a reduction of intragranular defects that minimized carrier recombination. The optimized CH3NH3PbI3 films exhibited enhanced crystallinity, excellent carrier transport and injection, as well as suppressed charge recombination. Benefiting from these advantages, PSCs based on the optimized perovskite films delivered a power conversion efficiency of 17.99% and a stabilized power output above 17.30%. This study presents an effective strategy for the fabrication of high-quality, hybrid perovskite films with potential applications in optoelectronic devices.
Two pseudohalide thiocyanate ions (SCN⁻) have been used to replace two iodides in CH3NH3PbI3, and the resulting perovskite material was used as the active material in solar cells. In accelerated stability tests, the CH3NH3Pb(SCN)2I perovskite films were shown to be superior to the conventional CH3NH3PbI3 films as no significant degradation was observed after the film had been exposed to air with a relative humidity of 95% for over four hours, whereas CH3NH3PbI3 films degraded in less than 1.5 hours. Solar cells based on CH3NH3Pb(SCN)2I thin films exhibited an efficiency of 8.3%, which is comparable to that of CH3NH3PbI3 based cells fabricated in the same way.
Altering cation and anion ratios in perovskites has been an excellent avenue in tuning the perovskite properties and enhancing the performance. Recently, MA/FA/Cs triple cation mixed halide perovskites have demonstrated efficiencies reaching up to 22 %. Similar to the widely explored MAPbI3, excess PbI2 is added in these perovskite films to enhance the performance. Previous reports demonstrate that the excess PbI2 is beneficial for the performance. However, not much work has been conducted about its impact on stability. Triple cation perovskites (TCP) deploy excess PbI2 up to 8 %. Thus, it is imperative to analyze the role of excess PbI2 in the degradation kinetics. In this paper, we have varied the amount of PbI2 in the triple cation perovskite films and monitored the degradation kinetics by X-ray diffraction (XRD) and optical absorption spectroscopy. We found that the inclusion of excess PbI2 adversely affects the stability of the material. Faster degradation kinetics is observed for higher PbI2 samples. However, excess PbI2 samples showed superior properties such as enhanced grain sizes and better optical absorption. Thus, careful management of the PbI2 quantity is required to obtain better stability and alternative pathways should be explored to achieve better device performance rather than adding excess PbI2.
High quality perovskite films can be fabricated from Lewis acid-base adducts through molecule exchange. Substantial work is needed to fully understand the formation mechanism of the perovskite films, which help to further improve their quality. Here, we study the formation of CH3NH3PbI3 perovskite films by introducing some dimethylacetamide into PbI2/N,N-dimethylformamide solution. We reveal that there are three key processes during the formation of perovskite films through the Lewis acid-base adduct approach: molecule intercalation of solvent into PbI2 lattice, molecule exchange between the solvent and CH3NH3I, and dissolution-recrystallization of the perovskite grains during annealing. The Lewis base solvents play multiple functions in the above processes. The properties of solvent, including Lewis basicity and boiling point, play key roles in forming smooth perovskite films with large grains. We also provide some rules for choosing Lewis base additives in order to prepare high quality perovskite films through the Lewis adduct approach.
Metal halide perovskite solar cells have now reached efficiencies of over 22%. To date, the most efficient perovskite solar cells have the n-i-p device architecture, and use 2,2’,7,7’-tetrakis(N,N’-di-p-methoxyphenylamine)-9,9’-spirobifluorene or poly(triarylamine) as the hole transport material (HTM), which are typically doped with lithium bis((trifluotomethyl)sulfonyl)amide (Li-TFSI). Li TFSI is hygroscopic and detrimental to the long-term performance of the solar cells, limiting its practical use. In this work, we successfully replace Li-TFSI by molybdenum tris-(1-(methoxycarbonyl)-2-(trifluoromethyl)ethane-1,2-dithiolene), Mo(tfd CO2Me)3, or molybdenum tris-(1-(trifluoroacetyl)-2-(trifluoromethyl)ethane-1,2-dithiolene), Mo(tfd-COCF3)3. With these two dopants, we achieve stabilized power conversion efficiencies up to 16.7% and 15.7% with average efficiencies of 14.8% ± 1.1% and 14.4% ± 1.2% respectively. Moreover, we observe a significant enhancement of the long-term stability of perovskite solar cells, under 85 ˚C thermal stressing in air.
Certified power conversion efficiencies (PCEs) of perovskite solar cells have increased to reach an impressive 22.1%. However, there exists microscopic inhomogeneity that limits high PCE, primarily as a result of defects at grain interiors and boundaries of perovskite films. Here, we report a strategy for reducing heterogeneity by using a bifunctional non-volatile Lewis base additive urea. The addition of 4 mol % urea results in significant enhancement of the macroscopic photoluminescence lifetime from 200.5 to 752.4 ns and elimination of trap-mediated non-radiative recombination, resulting in an improved PCE. The Lewis base urea is found to interact with solution precursors to retard crystal growth and enhance crystallinity, which subsequently precipitates at grain boundaries to passivate defects after completion of crystal growth. The resulting perovskite films show superior homogeneity in conductivity at both grain interior and boundaries in comparison with the bare perovskite films.
With the rapid development of organic-inorganic lead halide perovskite photovoltaics, increasingly more attentions are paid to explore the growth mechanism and precisely control the quality of perovskite films. In this study, we propose a “stitching effect” to fabricate high quality perovskite films by using chlorobenzene (CB) as an anti-solvent and isopropyl alcohol (IPA) as an additive into this anti-solvent. Because of the existence of IPA, CB can be efficiently released from the gaps of perovskite precursors and the perovskite film formation can be slightly modified in a controlled manner. More homogeneous surface morphology and larger grain size of perovskite films were achieved via this process. The reduced grain boundaries ensure low surface defect density and good carrier transport in the perovskite layer. Meanwhile, we also performed the Fourier transform infrared (FTIR) spectroscopy to investigate the film growth mechanism of unannealed and annealed perovskite films. Solar cells fabricated by using the “stitching effect” exhibited a best efficiency of 19.2%. Our results show that solvent and solvent additives dramatically influenced the formation and crystallization processes for perovskite materials due to their different coordination and extraction capabilities. This method presents a new path towards controlling the growth and morphology of perovskite films.