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A compact TiO2 layer is crucial to achieve high-efficiency perovskite solar cells. In this study, we developed a facile, low-cost and efficient method to fabricate a pinhole-free and ultrathin blocking layer based on highly crystallized TiO2 quantum dots (QDs) with an average diameter of 3.6 nm. The surface morphology of the blocking layer and the...
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... inside the solar cell. The largest R sh value for the device based on QD-CL indicates that short circuits or current leakages are minimized. 36 Higher R sh and lower R s values enable a larger FF and a high electron mobility. 34 These results are in good agreement with the conclusion drawn by analyzing the solar cells' performances. As shown in Fig. 7, we used a simple model (equivalent circuit is shown in the inset) capable of producing a good fit to the experimental data. 37 The radius of the impedance semi- circles corresponds to the internal resistance of the TiO 2 / CH 3 NH 3 PbI 3 interface, the TiO 2 layer itself and the FTO/TiO 2 interface. 38 The PSC with QD-CL exhibits the ...
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Citations
... Metal oxide QDs are used by researchers as ETM for PSCs now, offering superior properties compared to current metal oxide materials. Table 4 lists the details of the devices [88][89][90][91][92][93][94][95][96][97][98]. In 2015, Ameen et al. [88] used ZnO QDs treated with an atmospheric plasma jet as ETL for flexible PSCs. ...
... In 2015, Tu et al. [89] prepared three ETMs (TiO 2 , TiCl 4 , TAA (titanium diisopropoxide bis(acetylacetonate)) by spin coating. Among them, the TiO 2 QDs performed well, as their low series resistance and high parallel resistance resulted in faster charge transfer and a final PCE of 16.97%, much higher than the PSCs based on TiCl 4 and TAA (Figure 8a). ...
As the third generation of new thin-film solar cells, perovskite solar cells (PSCs) have attracted much attention for their excellent photovoltaic performance. Today, PSCs have reported the highest photovoltaic conversion efficiency (PCE) of 25.5%, which is an encouraging value, very close to the highest PCE of the most widely used silicon-based solar cells. However, scholars have found that PSCs have problems of being easily decomposed under ultraviolet (UV) light, poor stability, energy level mismatch and severe hysteresis, which greatly limit their industrialization. As unique materials, quantum dots (QDs) have many excellent properties and have been widely used in PSCs to address the issues mentioned above. In this article, we describe the application of various QDs as additives in different layers of PSCs, as luminescent down-shifting materials, and directly as electron transport layers (ETL), light-absorbing layers and hole transport layers (HTL). The addition of QDs optimizes the energy level arrangement within the device, expands the range of light utilization, passivates defects on the surface of the perovskite film and promotes electron and hole transport, resulting in significant improvements in both PCE and stability. We summarize in detail the role of QDs in PSCs, analyze the perspective and associated issues of QDs in PSCs, and finally offer our insights into the future direction of development.
... As a result, they are widely used in PSCs because of their tunable energy bands and ease of preparation. Examples include TiO 2 QDs, ZnO QDs, and SnO 2 QDs [32,35,67,68], which are non-toxic, cost-effective, and have high charge mobility. PbS QDs have a large exciton Bohr radii, and they are able to absorb near-infrared light, enhancing the PCE of PSCs. ...
Perovskite solar cells (PSCs) are currently attracting a great deal of attention for their excellent photovoltaic properties, with a maximum photoelectric conversion efficiency (PCE) of 25.5%, comparable to that of silicon-based solar cells. However, PSCs suffer from energy level mismatch, a large number of defects in perovskite films, and easy decomposition under ultraviolet (UV) light, which greatly limit the industrial application of PSCs. Currently, quantum dot (QD) materials are widely used in PSCs due to their properties, such as quantum size effect and multi-exciton effect. In this review, we detail the application of QDs as an interfacial layer to PSCs to optimize the energy level alignment between two adjacent layers, facilitate charge and hole transport, and also effectively assist in the crystallization of perovskite films and passivate defects on the film surface.
... TiO 2 nanocrystals are used as electron transport layer. The specific synthesis method refers to the work of Tu et al. [46]. The obtained TiO 2 nanocrystals were dispersed in anhydrous chloroform and methanol (volume ratio 1:1) to obtain a TiO 2 colloidal solution (~5 mg‧mL -1 ) for later use. ...
Solar energy is clean, open, and infinite, but solar radiation on the earth is fluctuating, intermittent, and unstable. So, the sustainable utilization of solar energy needs the complementary combination of high-efficient energy conversion and low-loss energy storage technologies. Hence, a photocapacitor integrated with photo-electrical conversion and electric-chemical storage functions in single device is a cost-effective, volume-effective and functional-effective optimal choice. However, the highest reported conversion storage efficiency of single device is less than 13%. Here, we investigate the relationship among various efficiencies of photocapacitors during conversion storage process, and propose a function portfolio management concept. Accordingly, a three-terminal photocapacitor integrated with perovskite solar cell and symmetrical supercapacitor units is designed. By harmonizing the energy matching between conversion and storage units and seeking the maximum power points coincide and the maximum efficiency points synchronize, the solar energy conversion storage efficiency of the integrated photocapacitor surpasses milestone of 20%.
... showing high electric conductivity and large photocurrent in a solar cell device. 48 On the other hand, at n ¼ 13.13%, R S shows a slightly increased trend with a relatively large variation. This result may be due to the increase in the total resistance caused by the excessive thickness of the SnO 2 layer. ...
Optimization of carrier extraction and/or transport layers is an important factor for the development of perovskite semiconductor devices. In particular, tin dioxide, SnO 2 , is being frequently used as an electron transport layer (ETL) in perovskite solar cells. However, a systematic study on preparation and characterization of the SnO 2 -ETL is still lacking, and thus, morphological and electronic-functional roles are not fully understood. In this paper, we systematically investigate the SnO 2 -ETL prepared on fluorine-doped tin oxide (FTO) substrates by a spin-coating technique. Using microscopic observations, we morphologically study how the SnO 2 film covers the FTO surface with large unevenness. Optical characterizations are employed for investigating an electronic band alignment of the perovskite/SnO 2 interface varied with the SnO 2 concentration in a solution. Furthermore, we systematically evaluate photovoltaic properties of FTO-based solar cell devices. A major finding from these investigations is the fact that while the SnO 2 -ETL prepared at the adequate condition exhibits an ideal band alignment, the excessive SnO 2 deposition causes a poor electron extraction and device performance degradation. Furthermore, we show that the spin-coated SnO 2 -ETL can cover the FTO surface as an ultrathin wrapping layer. These results highlight the importance of the SnO 2 -ETL and pave the way for optoelectronic device applications of perovskite materials.
... Traditional electron transport materials (ETMs), such as TiO 2 , SnO 2 , ZnO, etc, have the properties of relatively low electron mobility, mismatched energy levels and so on [56]. These ETMs are prone to cracks during the film formation process, resulting in a large transport resistance [57][58][59]. Focusing on these problems, the researchers found that using nano-structured QDs as ETMs can effectively reduce defects of ETL and improve electron transport capability so that the PCE could be improved. The details of device performance based on QDs as ETM involved in this review are listed in table 2. ...
... Compared with traditional metal oxide materials, metal oxide QDs (MOQDs) show great advantages in promoting electron transport and improving PSCs performance. Tu et al (2015) used a TiO 2 QDs layer as an n-type barrier layer in the mesostructured PSCs, which had demonstrated an excellent charge injection characteristic and low transfer resistance [58]. The efficiency and stability of the corresponding device [61] were much higher than those of the traditional TiO 2 -device. ...
Perovskite solar cells (PSCs) are important candidates for next generation thin-film photovoltaic technology due to their superior performance in energy harvesting. At present, their photoelectric conversion efficiencies (PCEs) are comparable to those of silicon-based solar cells. PSCs have usually multi-layer structure. Therefore, they face the problem that the energy levels between adjacent layers often mismatch to each other. Meanwhile, large amount of defects are often introduced due to the solution preparation procedures. What's more, the perovskite is prone to degradation under ultraviolet (UV) irradiation. These problems could degrade the efficiency and stability of PSCs. In order to solve these problems, quantum dots (QDs), a kind of low-dimensional semiconductor material, have been recently introduced into PSCs as charge transport materials, interfacial modification materials, dopants and luminescent down shifting materials. By these strategies, the energy alignment and interfacial conditions are improved, the defects are efficiently passivated, and the instability of perovskite under UV irradiation is suppressed. So the device efficiency and stability are both improved. In this paper, we overview the recent progress of QDs' utilizations in PSCs.
... The colloidal TiO 2 quantum dots were prepared via a simple solvothermal method according to the previous literature. 38 The compact TiO 2 layer was deposited by spin-coating the colloidal solution onto the FTO glass at 4000 rpm for 60 s and then annealed at 500 C for 0.5 h. Aerwards, the substrates were moved to the N 2 -lled glove box. ...
As the most popular hole-transporting material (HTM), spiro-OMeTAD has been extensively applied in perovskite solar cells (PSCs). Unluckily, the pristine spiro-OMeTAD film has inferior conductivity and hole mobility, thus limiting its potential for application in high-performance PSCs. To ameliorate the electrical characteristics of spiro-OMeTAD, we employ 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as a strong electron acceptor into spiro-OMeTAD in PSCs. The incorporation of DDQ with spiro-OMeTAD not only improves the conductivity and the Fermi energy level, but also reduces the trap states and nonradiative recombination, which accounts for the remarkable enhancement in both the fill factor (FF) and open-circuit voltage (VOC) of PSCs. Consequently, the champion PSC with DDQ doped hole transport layer (HTL) generates a boosted power conversion efficiency (PCE) of 21.16% with an FF of 0.796 and a VOC of 1.16 V. Remarkably, DDQ modified devices exhibit superb device stability, as well as mitigated hysteresis. This study provides a facile and viable strategy for dopant engineering of HTL to realize highly efficient PSCs.
... To further study the effects of PTFE additive on our perovskite solar cell devices, electrochemical impedance spectroscopy was carried out in dark at the frequency range between 1 Hz and 10 6 Hz. Fig. 5 presents the Nyquist plots of PSCs with and without PTFE additive, where one semicircle represents the recombination resistance based on previous research [51,52] . The inset image illustrates the equivalent circuit where R 1 is attributed to the internal resistance, R 2 to the transfer resistance acquired from the first arc in high-frequency region, and R 3 resulted from the second arc corresponding to recombination resistance [53] . ...
Hybrid organic-inorganic perovskites have attracted tremendous attention for solar cells application due to their outstanding properties. However, further studies are still needed to fully address the career recombination at grain boundaries which lower the device performance, and its environmental stability issues. Fluorides additive engineering is found to be a good method to successfully passivate defects in perovskite film. Here, we developed a simple method to improve the device power conversion efficiency as well as its environmental stability, by introducing polytetrafluoroethylene (PTFE) additive within the perovskite organic precursor in a two-step deposition method. The built-in electric field effect induced by PTFE generate migration of photon-generated carriers, suppressing the electron-hole recombination improving short circuit current and then the photovoltaic performance. We obtained a maximum efficiency of 20.48% for PTFE5% -based PSC compared to the pristine one which was only 14.27%. Furthermore, it is also demonstrated that the PTFE-based PSCs device exhibits strong environmental stability. The device presented only 5% PCE loss over 42 days of storage in an ambient environment.
... Secondly, the compact TiO 2 blocking layer (c-TiO 2 ) was spin-coated onto FTO glasses with two-step program (700 rpm for 5 s with a ramp-up of 1000 rpm/s, sequentially with 4000 rpm for 25 s with a ramp-up of 2000 rpm/s), followed by sintering in a muffle furnace at 500°C for 30 min. c-TiO 2 was synthesized by a facile solvothermal reaction as the same as previous literature [30]. ...
Perovskite solar cells have developed rapidly in the past decades. However, there are large amounts of ionic defects at the surface and grain boundaries of perovskite films which are detrimental to both the efficiency and stability of perovskite solar cells. Here, an organic halide salt pyridinium iodide (PyI) is used in cation-anion-mixed perovskite for surface defect passivation. Different from the treatment with Lewis base pyridine (Py) which can only bind to the under-coordinated Pb ions, zwitterion molecule PyI can not only fill negative charged iodine vacancies, but also interact with positive charged defects. Compared with Py treatment, PyI treatment results in smoother surface, less defect densities and non-radiative recombination in perovskite, leading to an improved VOC, negligible J-V hysteresis and stable performance of devices. As a result, the champion PyI-treated planar perovskite solar cell with a high VOC of 1.187 V achieves an efficiency of 21.42%, which is higher than 20.37% of Py-treated device, while the pristine device without any treatment gets an efficiency of 18.83% at the same experiment conditions.
... 6,7 The important function of common ETL, such as titanium dioxide (TiO 2 ) and zinc oxide (ZnO), can provide an electron pathway from perovskite to electrode and also reduce recombination rate of electron-hole pairs. 8,9 It should be noted that most efficient planar perovskite cells were fabricated using TiO 2 thin films as the ETL. 10 High PCEs of over 20% of perovskite solar cells have been reported for only with the laboratory scales within a few years ago. [11][12][13][14] Remarkably, the reported certified PCEs of perovskite solar cells at 25.2% from the National Renewable Energy Laboratory (NREL) chart 15 are catching up the PCEs of silicon solar cells. ...
Perovskite solar cells have been attracted as new representatives for the third-generation photovoltaic devices. Simple strategies for high efficiency with the long-term stability of solar cells are the challenges for commercial solar cell technology. Another challenge of the development toward industrial scale in perovskite solar cells is the production under the ambient and high humidity. In this sense, we successfully fabricated perovskite solar cells via solution depositions of all layers under ambient air with a relative humidity above 50%. Titanium dioxide (TiO 2 ) nanoparticles with the roles for efficient charge extraction and electron transportation properties were used as an electron-transporting layer in the cell fabrication. The modification of TiO 2 nanoparticles for energy band adjustment was done by doping with nontoxic cadmium sulfide (CdS) quantum dots. With the variation of CdS concentrations, energy band is not only changeable, but the enhancement of the perovskite solar cells efficiency could be achieved compared with the conventional cells made of pristine-TiO 2 film and TiO 2 nanoparticles.
... Its relatively wide band gap (~3.20 eV) is the main limitation for its industrial application, which means that TiO 2 can only be activated by irradiation with a wavelength less than 387 nm and is sensitive to UV light [8][9][10][11]. A lot of research efforts, such us sensitization, doping rare metal ion, doping metalloid, and coupling semiconductor [12][13][14][15][16], have been made all around the world in order to extend the application of TiO 2 . It has been proved that noble metals of Au, Ag, Pt, and Pd deposited onto the surface of TiO 2 can modify the surface properties of the material and enhance the catalytic capability [17,18]. ...
Abstract In the present work, polyaniline and CeO2 co-decorated TiO2 nanotube arrays (PANI/CeO2/TiO2 NTAs) were facilely prepared by an electrochemical method. The as-prepared materials were characterized by scanning electron microscopy (SEM), an X-ray diffractometer (XRD), and energy-dispersive X-ray spectroscopy (EDS). The photoelectrocatalytic activity of as-prepared materials was investigated with tetrabromobisphenol A (TBBPA) as the target analyte, and the data showed that PANI/CeO2/TiO2 NTAs resulted in much higher photoelectrocatalytic efficiency than that of other materials. Under optimal conditions, the degradation rate of TBBPA reached a maximum value over 96% in 120 min under simulated solar irradiation. The results indicated that CeO2 and PANI co-modified TiO2 NTAs could narrow the band gap, expand the response from ultraviolet (UV) to visible region, increase the amount of active free radicals, inhibit the recombination rate of electron-hole pairs, and finally enhance the degradation efficiency towards TBBPA owing to the presence of Ce3+/Ce4+ and PANI. Moreover, the degradation reaction followed the first-order kinetics, and degradation rates of the repeated experiments were all over 92% for ten runs. All these results indicated that this novel catalyst earned great potential as a powerful photoelectrocatalyst for the removal of TBBPA and other pollutants.
