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Advancing Optoelectronic Performance of Organic Solar Cells: Computational Modeling of Non-Fullerene Donor Based on End-Capped Triphenyldiamine (TPDA) Molecules
... Extensive research has been conducted on non-fullerene bulk heterojunction (BHJ) organic photovoltaic cells (OPVs) as viable alternatives to phenyl-C60 (or C70) butyric acid methyl ester (PC60BM or PC70BM). The aim of this study was to identify potential alternatives to PC60BM and PC70BM that are electron-accepting small molecules (SMs) [36][37][38][39]. ...
... It has been established that increased branching not only enhances optoelectronic properties but also extends conjugation in the terminal acceptor or donor region, leading to similar outcomes [39,[45][46][47].Previous research has demonstrated that IDT-BT possesses highly favorable optoelectronic characteristics, primarily due to its high extinction coe cients around 650 nm. In this current study, our objective is to investigate the theoretical performance of non-fullerene solar cells (NFSCs) by creating a con guration known as A-D-A. ...
Five rhodanine-based small molecule (SMs) photovoltaic materials (A1-A5) were rigorously manufactured and methodically evaluated to evaluate their optoelectronic characteristics as donor moiety in organic solar cells (OSCs) compared to O-IDTBR. The newly developed compounds (A1-A5) possess electron-withdrawing functional groups on both terminal ends of the reference molecule (Ref). After a benchmark study, simulations performed at MPWPW91/6-311G (d, p). A2 exhibited the lowest energy gap (Eg) of 1.818 eV and largest dipole moment of 13.43 D in dichloromethane solvent. A2 photophysical characteristics predict good miscibility and performance. The unique molecules demonstrate superior open-circuit voltage (VOC), the lowest band gap, elevated absorption spectra, and power conversion efficiency (PCE) explore to the reference material, hence enhancing operational efficiency. The reference molecule (Ref) PCE is 18.30%, but newly developed compounds have PCEs from 11.47–21.11%. Thus, Ref molecule terminal structural changes can improve solar material efficiency. PSCs and OSCs use small-molecule hole transporting materials (HTMs) as donor contributors in this solar energy research achievement.
... Bond length "L C-C " (Å) Higher electronic excitations result in a more efficient charge transfer as a result of electrons' increased ability to absorb energy and move to higher energy states [64]. Tables 5 and 6 indicate that molecules in the chloroform exhibit significantly higher excitation energies than those in the gaseous medium, which results from the polarization effect caused by the solvent. ...
Modification of terminal acceptors of non-fullerene organic solar cell molecule with different terminal acceptors can help in screening of molecules to develop organic photovoltaic cells with improved performance. Thus, in this work, seven new molecules with an unfused core have been designed and thoroughly investigated. DFT/TD-DFT simulations were performed on studied molecules to explore the ground and excited state characteristics. UV–Visible analysis revealed the red shift in the absorption spectrum (reaching 781 nm) owing to their smaller energy gap up to 1.94 eV. Furthermore, transition density matrix analysis demonstrated that peripheral acceptors extract the electron density from the core effectively. The effectiveness of our investigated molecules as materials for high-performing organic photovoltaic cells has been shown by an examination of their electron and hole mobilities for fast charge transfer. When combined with PTB7-Th, all molecules displayed high open circuit voltage. XP5 molecule exhibited highest open circuit voltage (1.70 eV) and lowest energy loss of 0.30 eV. All designed molecules exhibit the improved aforementioned parameters, which shows that these molecules can be used to develop competent solar devices in future.
... The newly designed molecules involve the effective participation of π-conjugated donor-bridge-acceptor moieties in light absorption and CT phenomena. This includes ground state HOMOs (highest occupied molecular orbitals) that have the ability to donate electrons and excited state LUMOs (lowest unoccupied molecular orbitals) that have the ability to accept electrons [48,49]. To encourage the CT from the central donor section of HOMO to the terminal acceptor part of LUMO, as indicated in reference SR, LUMO density is located on terminal groups and HOMO charge density is focused in the middle area of the core. ...
Context
The purpose of the S01-S05 series of end-capped modified donor chromophores is to amplify the energy conversion efficiency of organic solar cells. Using quantum chemical modeling, the photophysical and photoelectric characteristics of the S01-S05 geometries are examined.
Method
The influence of side chain replacement on multiple parameters, including the density of states (DOS), molecular orbital analysis (FMOS), Exciton binding energy (Eb), Molecular electrostatic potential analysis, Dipole moment (µ), and photovoltaic characteristics including open circuit voltage (VOC), and PCE at minimal energy state geometries, has been investigated employing density functional theory along with TD-DFT analysis. The molar absorption coefficient (λmax) of all the proposed compounds (S01-S05) were efficiently enhanced by the terminal acceptor alteration technique, as demonstrated by their scaling up with the reference molecule (SR). Among all molecules, S04 has shown better absorption properties with a red shift in absorption having λmax at 845 nm in CHCl3 solvent and narrow energy gap (EG) 1.83 eV with least excitation energy (Ex) of 1.4657 eV. All created donors exhibited improved FF and VOC than the SR, which significantly raised PCE and revealed their great efficiency as OSC. Consequently, the results recommended these star-shaped molecules as easily attainable candidates for constructing extremely efficient OSCs.
... We altered the end (BDPTT) core group in this study due to a number of circumstances. First off, from a synthetic standpoint, end groups are simpler to replace or modify than central cores [25][26][27][28][29]. Second, they have a big impact on mix morphologies, energies, charge transfer kinetics, and electron affinity. ...
... It also effectively explains the distribution array of charge transportation in solar cells. [36][37][38][39] The HOMO denotes as valence band (VB), whereas the LUMO refers to the conduction band (CB). The FMO energy gap is a demonstrative signature in PV devices. ...
The current quantum mechanical study is focused on the fabrication of eight helicene‐phenylamine‐based molecules (MPAM1–MPAM8) to investigate their photovoltaic (PV) and optoelectronic properties for photovoltaic cells (PVCs). The outcomes revealed that fabricated chromophores showed deeper highest occupied molecular orbital levels, higher solubility, low exciton binding energy, greater hole mobility with low band gap energy than the model compound (MPAR). Moreover, the reorganization energy values interpret that newly fabricated compounds possess high charge mobility compared to the representative molecule (MPAR) which encourages their usage as HTM in PSCs. All the freshly designed molecules revealed greater estimated open circuit voltage values contrasted to the reference molecule (MPAR) which ensures their prominent working efficacy. The results signify the competence of this strategic approach, paving a new path for the fabrication of hole transport material (HTM) for perovskite solar cells (PSCs) and donor molecules for organic solar cells (OSCs).
... Fullerene derivatives like PCBM and PCBM70 are extensively utilized as electron acceptors, whereas NFAs such as ITIC and IDIC have arisen as substitutes for fullerene derivatives. Small organic molecules with specified functional groups and polymers with bespoke end-capping moieties can also be employed [13][14][15]. The preference for end-capping molecules is contingent upon the particular necessities of the solar cell and can markedly affect its efficiency, stability, and global performance. ...
... The solubility is assuredly linked to the smooth configuration of molecular fragments. A higher dipole moment is also estimated to enhance charge separation, leading to a productive charge transport rate between donor and acceptor moiety [75]. Dipole moments of model and novel molecules are computed at chosen hybrid functional (MPW1PW91), and values are listed in Table 4 for both gaseous and solvent mediums. ...
Improving the light-harvesting efficiency and boosting open circuit voltage are crucial challenges for enhancing the efficiency of organic solar cells. This work introduces seven new molecules (SA1-SA7) to upgrade the optoelectronic and photovoltaic properties of Q-C-F molecule-based solar cells. All recently designed molecules have the same alkyl-substituted quinoxaline core and CPDT donor but vary in the end-capped acceptor subunits. All the investigated molecules have revealed superior properties than the model (R) by having absorbance ranging from 681 nm to 782 nm in the gaseous medium while 726 nm – 861 nm in chloroform solvent, with the lowest band gap ranging from 1.91-2.19 eV. SA1 molecule demonstrated the highest λmax (861 nm) in chloroform solvent and the lowest band gap (1.91 eV). SA2 molecule has manifested highest dipole moment (4.5089 D), lower exciton binding energy in gaseous (0.33 eV) and chloroform solvent (0.47 eV), and lower charge mobility of hole (0.0077693) and electron (0.0042470). At the same time, SA7 showed the highest open circuit voltage (1.56 eV) and fill factor (0.9166) due to solid electron-pulling acceptor moieties. From these supportive outcomes, it is inferred that our computationally investigated molecules may be promising candidates to be used in advanced versions of OSCs in the upcoming period.
... In view of the fact that these interactions lead to a donation of occupancy from the localized NBOs of the idealized Lewis structure into the empty non-Lewis orbitals, they are referred to as "delocalization" corrections to the zeroth-order natural Lewis structure. For each donor, NBO (i) and acceptor NBO (j), the stabilization energy E(2) associated with delocalization ("2e-stabilization") i-j is estimated as [47,[57][58][59], in which F(i, j) is the off-diagonal NBO Fock matrix element, q i is the donor orbital occupancy, ε j , and ε i are diagonal elements (orbital energies), and q i is the donor orbital occupancy. The molecular system's more extensive conjugation is a result of the stability energy's higher levels. ...
ContextThe present study aims to improve the performance of optoelectronics and photovoltaics by constructing an acceptor–donor-acceptor (A-D-A) molecule with a fullerene-free acceptor moiety. The study utilizes malononitrile and selenidazole derivatives to tailor the molecule for enhanced photovoltaic abilities. The study analyzes molecular properties and parameters like charge density, charge transport, UV absorption spectra, exciton binding energies, and electron density difference maps to determine the effectiveness of the tailored derivatives.Methods
To optimize the geometric structures, the study used four different functionals (B3LYP, CAM-B3LYP, MPW1PW91, and ɷB97XD) along with a double zeta valence basis set 6-31G(d, p) basis set. The study compared the results of the tailored derivatives with a reference molecule (R-P2F) to determine improvements in performance. The light harvesting efficiency of the molecules was analyzed by performing simulations in the gas and solvent phases (chloroform) based on the spectral overlap between the solar irradiance and the absorption spectra of the molecules. The open-circuit voltage (VOC) of each molecule was also analyzed, representing the maximum voltage that can be obtained from the cell under illuminated conditions. The findings indicated that the M1-P2F designed derivative is a more effective, with energy gap of 2.14 eV, and suitable candidate for non-fullerene organic solar cell application, based on various analyses such as power conversion efficiency, quantum chemical reactivity parameters, and electronic features.
Designing efficient, non-fused ring-based organic solar cells (OSCs) with high open circuit voltage is a significant challenge. The present research proposes seven novel moieties generated from an existing 4T2CSi-4F (R) asymmetric molecule to increase efficiency. The density functional theory (DFT) was used to examine several essential characteristics like optical, electronic, and efficiency-related properties of molecules. It is revealed that newly presented molecules have superior features that are required to manufacture efficient organic solar cells. They exhibit a lower band gap between 2.05 – 2.34 eV and have a planar shape. Six moieties exhibit lower excitation energy in the gas and chloroform phases, and five moieties have more excellent dipole moments than the R molecule. UA1 and UA2 show remarkable enhancement in the optoelectronic properties, exhibiting the greater λmax at 773 nm and a smaller excitation energy of 1.60 eV. All the newly presented molecules have lower ionization potential and reorganization energies of the electron. The open circuit voltage (Voc) of five newly designed molecules is greater, varying from 1.40 to 1.55 eV, than R (Voc=1.38 eV). Furthermore, the newly designed molecules, except UA1 and UA2, show more excellent fill factor (FF) than the R molecule. This significant increase in efficiency-associated metrics (FF and Voc) suggests that these molecules may be effectively implemented to manufacture an upgraded version of OSCs.
Organic solar cells (OSCs) made of electron-acceptor and electron-donor materials have significantly developed in the last decade, demonstrating their enormous potential in cutting-edge optoelectronic applications. Consequently, we designed seven novel non-fused ring electron acceptors (NFREAs) (BTIC-U1 to BTIC-U7) using synthesized electron-deficient diketone units and reported end-capped acceptors, a viable route for augmented optoelectronic properties. The DFT and TDDFT approaches were used to measure the power conversion efficiency (PCE), open circuit voltage (Voc), reorganization energies (λh, λe), fill factor (FF), light harvesting efficiency (LHE) and to evaluate the potential usage of proposed compounds in solar cell applications. The findings confirmed that the photovoltaic, photophysical, and electronic properties of the designed molecules BTIC-U1 to BTIC-U7 are superior to those of reference BTIC-R. The TDM analysis demonstrates a smooth flow of charge from the core to the acceptor groups. Charge transfer analysis of the BTIC-U1:PTB7-Th blend revealed orbital superposition and successful charge transfer from HOMO (PTB7-Th) to LUMO (BTIC-U1). The BTIC-U5 and BTIC-U7 outperformed the reference BTIC-R and other developed molecules in terms of PCE (23.29% and 21.18%), FF (0.901 and 0.894), normalized Voc (48.674 and 44.597), and Voc (1.261 eV and 1.155 eV). The proposed compounds enclose high electron and hole transfer mobilities, making them the ideal candidate for use with PTB7-Th film. As a result, future SM-OSC design should prioritize using these constructed molecules, which exhibit excellent optoelectronic properties, as superior scaffolds.
Minimizing energy loss is of critical importance in the pursuit of attaining high-performance organic solar cells. Interestingly, reorganization energy plays a crucial role in photoelectric conversion processes. However, the understanding of the relationship between reorganization energy and energy losses has rarely been studied. Here, two acceptors, Qx-1 and Qx-2, were developed. The reorganization energies of these two acceptors during photoelectric conversion processes are substantially smaller than the conventional Y6 acceptor, which is beneficial for improving the exciton lifetime and diffusion length, promoting charge transport, and reducing the energy loss originating from exciton dissociation and non-radiative recombination. So, a high efficiency of 18.2% with high open circuit voltage above 0.93 V in the PM6:Qx-2 blend, accompanies a significantly reduced energy loss of 0.48 eV. This work underlines the importance of the reorganization energy in achieving small energy losses and paves a way to obtain high-performance organic solar cells. Minimising energy loss is important for achieving high-performance organic solar cells. Here, the authors design and synthesise two acceptors with small reorganisation energies and reveal the relationship between reorganisation energy and energy losses.
Designing molecular materials with very large exciton diffusion lengths would remove some of the intrinsic limitations of present-day organic optoelectronic devices. Yet, the nature of excitons in these materials is still not sufficiently well understood. Here we present Frenkel exciton surface hopping, an efficient method to propagate excitons through truly nano-scale materials by solving the time-dependent Schrödinger equation coupled to nuclear motion. We find a clear correlation between diffusion constant and quantum delocalization of the exciton. In materials featuring some of the highest diffusion lengths to date, e.g. the non-fullerene acceptor Y6, the exciton propagates via a transient delocalization mechanism, reminiscent to what was recently proposed for charge transport. Yet, the extent of delocalization is rather modest, even in Y6, and found to be limited by the relatively large exciton reorganization energy. On this basis we chart out a path for rationally improving exciton transport in organic optoelectronic materials.
Organic compounds having significant nonlinear optical (NLO) applications are being employed in the optoelectronics field. In the current work, a series of non-fullerene acceptor (NFA) based compounds are designed by modifying the acceptors with different substituents using DTS(FBTTh 2 ) 2 R1 as a reference compound. To study the NLO responses to the tuning of various acceptors, DFT and TD-DFT based parameters were calculated at the M06 level along with the 6-31G(d,p) basis set. The designed compounds (MSTD2-MSTD7) showed smaller values of the energy gap in comparison to the reference compound. The energy gaps of the title compounds were linked to global reactivity insights; MSTD7 provided a lower band gap, with smaller and larger quantities for hardness and softness characteristics, respectively. Further, UV-vis analyses were performed for all of the designed compounds, displaying wavelengths red-shifted from that of DTS(FBTTh 2 ) 2 R1 . The intraelectron transfer (ICT) process and stability of the title compounds were explored via frontier molecular orbital (FMO) and natural bond orbital (NBO) studies, respectively. Out of all the designed compounds, the highest value of linear polarizability ⟨α⟩ of 3.485 × 10-22 esu, first hyperpolarizability (βtotal) of 13.44 × 10-27 esu and second-order hyperpolarizability ⟨γ⟩ of 3.66 × 10-31 esu were exhibited by MSTD7. In short, all of the designed compounds exhibited promising NLO properties because of their low charge transport resistance. These NLO properties may be useful for experimental researchers to uncover NLO materials for modern applications.
Enhancing the luminescence property without sacrificing the charge collection is one key to high-performance organic solar cells (OSCs), while limited by the severe non-radiative charge recombination. Here, we demonstrate efficient OSCs with high luminescence via the design and synthesis of an asymmetric non-fullerene acceptor, BO-5Cl. Blending BO-5Cl with the PM6 donor leads to a record-high electroluminescence external quantum efficiency of 0.1%, which results in a low non-radiative voltage loss of 0.178 eV and a power conversion efficiency (PCE) over 15%. Importantly, incorporating BO-5Cl as the third component into a widely-studied donor:acceptor (D:A) blend, PM6:BO-4Cl, allows device displaying a high certified PCE of 18.2%. Our joint experimental and theoretical studies unveil that more diverse D:A interfacial conformations formed by asymmetric acceptor induce optimized blend interfacial energetics, which contributes to the improved device performance via balancing charge generation and recombination. High-performance organic solar cells call for novel designs of acceptor molecules. Here, He et al. design and synthesize a non-fullerene acceptor with an asymmetric structure for diverse donor:acceptor interfacial conformations and report a certificated power conversion efficiency of 18.2%.
Many researchers are engaged nowadays in developing efficient photovoltaic materials to accomplish the demand of modern technology. Nonfullerene small molecular acceptors (NF-SMAs) show potential photovoltaic performance, accelerating the development of organic solar cells (OSCs). Herein, the first theoretical designing of a series of indacenodithiophene-based (IDIC1-IDIC6) acceptor chromophores was done by structural tailoring with various well-known acceptors from the recently synthesized IDICR molecule. For the selection of the best level of density functional theory (DFT), various functionals such as B3LYP, M06-2X, CAM-B3LYP, and ωB97XD with the 6-311G(d,p) basis set were used for the UV-visible analysis of IDICR. Consequently, UV-visible results revealed that an interesting agreement was found between experimental and DFT-based values at the B3LYP level. Therefore, quantum chemical investigations were executed at the B3LYP/6-311G(d,p) level to evaluate the photovoltaic and optoelectronic properties. Structural tailoring with various acceptors resulted in a narrowing of the energy gap (2.245-2.070 eV) with broader absorption spectra (750.919-660.544 nm). An effective transfer of charge toward lowest unoccupied molecular orbitals (LUMOs) from highest occupied molecular orbitals (HOMOs) was studied, which played a crucial role in conducting materials. Further, open circuit voltage (V oc) analysis was performed with respect to HOMO PBDB-T -LUMOACCEPTOR, and all of the derivatives exhibited a comparable value of voltage with that of the parent chromophore. Lower reorganization energies in titled chromophores for holes and electrons were examined, which indicated the higher rate of mobility of charges. Interestingly, all of the designed chromophores exhibited a preferable optoelectronic response compared to the reference molecule. Therefore, this computed framework demonstrates that conceptualized chromophores are preferable and might be used to build high-performance organic solar cells in the future.
Die π‐konjugierte ionische Verbindung QAPyBF4 wird im Forschungsartikel von Juin‐Jei Liou, Taiho Park, Zong‐Xiang Xu et al. als Perowskit‐Modulator vorgestellt (DOI: 10.1002/ange.202117303). Experimentelle Studien zeigen, dass konjugierte p‐Typ‐Kationen [QAPy]2+ an der Perowskit‐Oberfläche adsorbieren, an der unterkoordinierte Pb‐Kationen und [BF4]−‐Anionen an der SnO2‐Grenzfläche angereichert sind. Dieser spontane Diffusionseffekt von Kationen und Anionen verbessert die Bandausrichtung an zwei benachbarten Perowskit‐Grenzflächen und verringert Rekombinationsverluste.
Harnessing energy from the sun is attracting increasing attention as the traditional fossil-based energy sources are being depleted. Photovoltaics (PV) is now an established technology and the most promising method...
Defects and energy offsets at the bulk and heterojunction interfaces of perovskite are detrimental to the efficiency and stability of perovskite solar cells (PSCs). Herein, we designed an amphiphilic π‐conjugated ionic compound (QAPyBF4), implementing simultaneous defects passivation and interface energy level alignments. The p‐type conjugated cations passivated the surface trap states and optimized energy alignment at the perovskite/hole transport layer. The highly electronegative [BF4]⁻ enriched at the SnO2 interface featured desired band alignment due to the dipole moment of this interlayer. The planar n‐i‐p PSC had an efficiency of 23.1 % with Voc of 1.2 V. Notably, the synergy effect elevated the intrinsic endothermic decomposition temperature of the perovskite. The modified devices showed excellent long‐term thermal (85 °C) and operational stability at the maximum power point for 1000 h at 45 °C under continuous one‐sun illumination with no appreciable efficiency loss.
The development of novel photovoltaic materials for solar cell applications is a fascinating area of current research. Star-shaped materials with promising photovoltaic features have attracted scientists for boosting the progress of organic solar cells (OSCs). Herein, seven novel star-shaped molecules (DA1-DA7) are developed quantum chemically from the experimentally synthesized BTI(2 T-DCV-Hex)3 molecule. The open-circuit voltage (Voc), transition density matrix heat maps, density of state (DOS), overlap DOS, frontier molecular orbital, UV−visible, binding energy (Eb), hole (λh) and electron (λe) reorganizational energy, and highest occupied molecular orbital (HOMO)donor−lowest unoccupied molecular orbital (LUMO)PC61BM charge transfer analysis are performed to explore the optoelectronic properties. Newly developed molecules exhibit promising optoelectronic features with reduced energy gap (2.43−1.97 eV), transition energy (1.89−1.45 eV), λe (0.00149328−0.00101405 Eh), λh (0.0066471−0.0028843 Eh), broadened λmax (655−856 nm), and high Voc (2.07−1.65 V), as compared with reference BTI(2 T-DCV-Hex)3 values 2.82 eV, 2.28 eV, 0.00176501 Eh, 0.0060877 Eh, and 544 nm, 1.65 V, respectively. The developed molecules have proficient hole and electron transfer mobilities and can serve as best candidates when blended with PC61BM film. These eye-catching results recommend the novel star-shaped compounds for future development of high-performance OSCs.
Organic solar cells (OSCs) have received much attention because of their versatile advantages including solution process ability, flexibility, transparency, and lightweight. Fullerene-free acceptor molecules are efficiently utilized in organic solar cells due to their perfect symmetry with donor polymer. In this study, modifications of fullerene-free acceptor molecules have been done using efficient end-capped units. Five new molecules have been designed and explored through DFT and TD-DFT approaches at MPW1PW91 method with 6-31G(d,p) level of theory. Analysis of frontier molecular orbitals, transition density matrix, open-circuit voltage, excitation and binding energies has been done for exploring the photovoltaic and opto-electric properties of the designed molecules. Electron and hole reorganization energies are also computed for examining the mobility of charge density in designed molecules. Results of different geometric analyses suggested that EC1 to EC5 are effective contributors for highly stable organic solar cells.
Graphical abstract
A perylene-based acceptor (PMI-FF-PMI), consisting of two perylene monoimide (PMI) units bridged with a dihydroindeno[1,2 b]fluorene molecule was developed as a potential non-fullerene acceptor (NFA) for organic solar cells (OSCs). The synthesized NFA was combined with the high-performance donor polymer D18 to fabricate efficient OSCs. With an effective bandgap of 2.02 eV, the D18:PMI-FF-PMI blend can be categorized as a wide-bandgap OSC and is an attractive candidate for the application as a wide-bandgap sub-cell in all-organic triple-junction solar cell devices. Owing to their large effective bandgap, D18:PMI-FF-PMI solar cells are characterized by an extremely high open-circuit voltage (VOC) of 1.41 V, which to the best of our knowledge is the highest reported value for solution-processed OSCs so far. Despite the exceptionally high VOC of this blend, a comparatively large non-radiative voltage loss (ΔVOCnon rad) of 0.25 V was derived from a detailed voltage loss analysis. Measurements of the electroluminescence quantum yield (ELQY) of the solar cell reveal high ELQY values of ~0.1 %, which is contradicting the ELQY values derived from the non-radiative voltage loss (ΔVOCnon-rad = 0.25 V, ELQY = 0.0063 %). This work should help to raise awareness that (especially for BHJ blends with small ΔHOMO or ΔLUMO offsets) the measured ELQY cannot be straightforwardly used to calculate the ΔVOCnon rad. To avoid any misinterpretation of the non-radiative voltage losses, the presented ELQY discrepancies for the D18:PMI-FF-PMI system should encourage OPV researchers to primarily rely on the ΔVOCnon rad values derived from the presented voltage loss analysis based on EQEPV and J-V measurements.
Four Acceptor-Donor-Accepter (A-D-A) type of triangular shaped sub-phthalocyanines (SubPcs) donor molecules namely SubPcs-EDM (sub-phthalocyanines-ethylidene di-malo-nonitrile as M1), SubPcs-ETFM (sub-phthalocyanines-ethylidene tetrafluoro-malononitrile as M2), SubPcs-ETFOM (sub-phthalocyanines-ethylidene tetrafluoro-oxo malononitrile as M3) and SubPcs-EOM (sub-phthalocyanines-ethylidene oxo malononitrile as M4) have been designed for computing its optoelectronic properties with state-of-the-art density functional theory B3LYP/LanL2DZ (d, p) model. In designed molecules, the non-fullerene acceptors are attached at the center of donor moieties. The SubPcs-ETFOM exhibited lowest band gap of energy 2.48 eV with broad absorption band at 645.53 nm. The open circuit voltage (V OC) of M3 is 2.55 V in comparison with phenyl-C 60-butyric acid methyl ester which abbreviated as PCBM. This computational study explains that engineered molecules
This research project centralized modeling and DFT analysis of reference (BTTR) and intended chromophores (BTTM1-BTTM5) based on benzotrithiophene (BTT) core to render them as economic competitors for solar cells. Substantial investigation on molecular levels of researched molecules had been accomplished by pursuing computational DFT and TD-DFT simulations to probe photovoltaic characteristics. MPW1PW91/6-311G (d,p) used to analytically observe molecules for their simulated values of absorption maximum, frontier molecular orbitals (FMOs), ionization potential (IP), electron affinity (EA), light harvesting efficiency (LHE), quantum chemical parameters i.e. chemical potential (μ0), chemical hardness η, chemical softness (S), electronegativity χ, and electrophilicity index (ω). Additionally, other geometric variables such as density of state (DOS), electrostatic potential (ESP), transition density matrix (TDM), binding energy (Eb), dipole moment (μ), reorganization energy (RE), and device performance (VOC) had been enumerated and contrasted with BTTR. Results uttered that all our modeled molecules (BTTM1-BTTM5) were preferential candidates for electronic properties as a consequence of red-shifted absorption maximum (662 nm) in CHCl3, narrow band gap (1.87 eV), lowest excitation energy (1.91 eV), highest μ (6.55 D), lowest Eb (0.52 eV) and chemically reactivity. Theoretically computed VOC values were found in the range of 1.14 to 1.38 eV with donor molecule PC61BM after successfully testing the compatibility of donor and acceptor interfaces. Because of the low RE values of electron (λe) and hole (λh) of designed chromophores, they exhibited magnified charge mobility. BTTM3 portrayed the lowest λe (0.005679 eV) and BTTM4 had explored the lowest λh (0.006637 eV). All designed chromophores (BTTM1-BTTM5) depicted intensified metrics computationally, which was a convincing rationale for their possible experimental usage in developing solar cell technology.
Applying an asymmetric strategy to construct non-fullerene small-molecule acceptors (NFSMAs) in organic solar cells (OSCs) plays a vital role in the development of organic photovoltaic materials. In the past several years, taking advantage of the larger dipole moment and stronger intermolecular interactions, asymmetric NFSMAs have witnessed tremendous progress in OSCs with a power conversion efficiency of over 18%. From a structural point of view, besides the possible changes in the conformation effect on molecular packing, asymmetric acceptors can also achieve a balance between the solubility and the crystallinity. Herein, we systematically investigate the structure–property–performance relationships of asymmetric NFSMAs that have recently emerged and try to clarify the feasibility and practicality of an asymmetric strategy for the design of higher-performance NFSMAs. Finally, we put forward our views and a concise outlook on the asymmetric strategy.
Device engineering is an effective way to improve the photovoltaic performance of organic solar cells (OSCs). Currently, the widely used bulk heterojunction (BHJ) structure has problems such as material solubility limitations and the emerging pseudoplanar heterojunction (PPHJ) structure is also troubled by printing technology requirements. However, these issues can be solved by the reasonable application of traditional planar heterojunction (PHJ) structure. Herein, PM6:BO-4F system is selected to prepare PHJ devices by combining sequential spin-coating and orthogonal solvent strategy. In view of the good solubility of PM6 and BO-4F in commonly used high-boiling solvent chlorobenzene (CB) and green solvent tetrahydrofuran (THF), respectively, the PHJ devices are successfully prepared by using these two orthogonal solvents, achieving a power conversion efficiency (PCE) of 15.6%. On this basis, green nonhalogen reagent o-xylene (O-XY) is further used to process PM6. Due to the large polarity difference between O-XY and THF, all-green solvent-processed PHJ devices are successfully fabricated and obtain an astonishing PCE of 16%. As far as it is known, it is the highest efficiency for PHJ OSCs. The results prove the huge research potential of PHJ structure and point out new direction for solving OSC materials compatibility, long-term stability, and future commercial applications.
The global need for renewable sources of energy has compelled researchers to explore new sources and improve the efficiency of the existing technologies. Solar energy is considered to be one of the best options to resolve climate and energy crises because of its long-term stability and pollution free energy production. Herein, we have synthesized a small acceptor compound (TPDR) and have utilized for rational designing of non-fullerene chromophores (TPD1–TPD6) using end-capped manipulation in A2–A1–D–A1–A2 configuration. The quantum chemical study (DFT/TD-DFT) was used to characterize the effect of end group redistribution through frontier molecular orbital (FMO), optical absorption, reorganization energy, open circuit voltage (Voc), photovoltaic properties and intermolecular charge transfer for the designed compounds. FMO data exhibited that TPD5 had the least ΔE (1.71 eV) with highest maximum absorption (λmax) among all compounds due to the four cyano groups as the end-capped acceptor moieties. The reorganization energies of TPD1–TPD6 hinted at credible electron transportation due to the lower values of λe than λh. Furthermore, open circuit voltage (Voc) values showed similar amplitude for all compounds including parent chromophore, except TPD4 and TPD5 compounds. These designed compounds with unique end group acceptors have the potential to be used as novel fabrication materials for energy devices.
Herein, we elucidate the photodegradation pathway of A‐D‐A‐type non‐fullerene acceptors for organic photovoltaics. Using IT‐4F as a benchmark example, we isolated the photoproducts and proved them isomers of IT‐4F formed by a 6‐e electrocyclic reaction between the dicyanomethylene unit and the thiophene ring, followed by a 1,5‐sigmatropic hydride shift. This photoisomerization was accelerated under inert conditions, as explained by DFT calculations predicting a triplet‐mediated reaction path (quenchable by oxygen). Adding controlled amounts of the photoproduct P1 to PM6:IT‐4F bulk heterojunction cells led to a progressive decrease in photocurrent and fill factor attributed to its poor absorption and charge transport properties. The reaction is a general photodegradation pathway for a series of A‐D‐A molecules with 1,1‐dicyanomethylene‐3‐indanone termini, and its rate varies with the structure of the donor and acceptor moiety.
Non-fullerene acceptors (NFAs) based on non-fused conjugated structures have more potential to realize low-cost organic photovoltaic (OPV) cells. However, their power conversion efficiencies (PCEs) are much lower than those of the fused-ring NFAs. Herein, a new bithiophene-based non-fused core (TT-Pi) featuring good planarity as well as large steric hindrance was designed, based on which a completely non-fused NFA, A4T-16, was developed. The single-crystal result of A4T-16 reveals that a three-dimensional interpenetrating network can be formed due to the compact π–π stacking between the adjacent end-capping groups. A high PCE of 15.2% is achieved based on PBDB-TF:A4T-16, which is the highest value for the cells based on the non-fused NFAs. Notably, the device retains ~84% of its initial PCE after 1300 h under the simulated AM 1.5 G illumination (100 mW cm−2). Overall, this work provides insight into molecule design of the non-fused NFAs from the aspect of molecular geometry control. Non-fullerene acceptors based on non-fused conjugated structures have potential for realizing low-cost organic photovoltaic cells, owing to its synthetic simplicity. Here, the authors develop a non-fused molecule with a three-dimensional interpenetrating network and compact π-π stacking, which is highly suitable for PV applications.
Organic solar cells (OSC) nowadays match their inorganic competitors in terms of current production but lag behind with regards to their open‐circuit voltage loss and fill‐factor, with state‐of‐the‐art OSCs rarely displaying fill‐factor of 80% and above. The fill‐factor of transport‐limited solar cells, including organic photovoltaic devices, is affected by material and device‐specific parameters, whose combination is represented in terms of the established figures of merit, such as θ and α. Herein, it is demonstrated that these figures of merit are closely related to the long‐range carrier drift and diffusion lengths. Further, a simple approach is presented to devise these characteristic lengths using steady‐state photoconductance measurements. This yields a straightforward way of determining θ and α in complete cells and under operating conditions. This approach is applied to a variety of photovoltaic devices—including the high efficiency nonfullerene acceptor blends—and show that the diffusion length of the free carriers provides a good correlation with the fill‐factor. It is, finally, concluded that most state‐of‐the‐art organic solar cells exhibit a sufficiently large drift length to guarantee efficient charge extraction at short circuit, but that they still suffer from too small diffusion lengths of photogenerated carriers limiting their fill factor.
As electrode work function rises or falls sufficiently, the organic semiconductor/electrode contact reaches Fermi-level pinning, and then, few tenths of an electron-volt later, Ohmic transition. For organic solar cells, the resultant flattening of open-circuit voltage (Voc) and fill factor (FF) leads to a ‘plateau’ that maximizes power conversion efficiency (PCE). Here, we demonstrate this plateau in fact tilts slightly upwards. Thus, further driving of the electrode work function can continue to improve Voc and FF, albeit slowly. The first effect arises from the coercion of Fermi level up the semiconductor density-of-states in the case of ‘soft’ Fermi pinning, raising cell built-in potential. The second effect arises from the contact-induced enhancement of majority-carrier mobility. We exemplify these using PBDTTPD:PCBM solar cells, where PBDTTPD is a prototypal face-stacked semiconductor, and where work function of the hole collection layer is systematically ‘tuned’ from onset of Fermi-level pinning, through Ohmic transition, and well into the Ohmic regime.
Typical organic semiconductor materials exhibit a high trap density of states, ranging from 1016 to 1018 cm−3, which is one of the important factors in limiting the improvement of power conversion efficiencies (PCEs) of organic solar cells (OSCs). In order to reduce the trap density within OSCs, a new strategy to design and synthesize an electron acceptor analogue, BTPR, is developed, which is introduced into OSCs as a third component to enhance the molecular packing order of electron acceptor with and without blending a polymer donor. Finally, the as‐cast ternary OSC devices employing BTPR show a notable PCE of 17.8%, with a low trap density (1015 cm−3) and a low energy loss (0.217 eV) caused by non‐radiative recombination. This PCE is among the highest values for single‐junction OSCs. The trap density of OSCs with the BTPR additives, as low as 1015 cm−3, is comparable to and even lower than those of several typical high‐performance inorganic/hybrid counterparts, like 1016 cm−3 for amorphous silicon, 1016 cm−3 for metal oxides, and 1014 to 1015 cm−3 for halide perovskite thin film, and makes it promising for OSCs to obtain a PCE of up to 20%. A facile strategy of employing an acceptor‐analogue is developed to efficiently reduce trap density to a magnitude of 1015 cm−3 for organic photovoltaic materials, which is comparable to and even lower than those of some inorganic counterparts, and boosts the power conversion efficiency of organic solar cells up to 17.8%.
Organic solar cells are composed of electron donating and accepting organic semiconductors. Whilst a significant palette of donors has been developed over three decades, until recently only a small number of acceptors have proven capable of delivering high power conversion efficiencies. In particular the fullerenes have dominated the landscape. In this perspective, the emergence of a family of materials–the non‐fullerene acceptors (NFAs) is described. These have delivered a discontinuous advance in cell efficiencies, with the significant milestone of 20% now in sight. Intensive international efforts in synthetic chemistry have established clear design rules for molecular engineering enabling an ever‐expanding number of high efficiency candidates. However, these materials challenge the accepted wisdom of how organic solar cells work and force new thinking in areas such as morphology, charge generation and recombination. This perspective provides a historical context for the development of NFAs, and also addresses current thinking in these areas plus considers important manufacturability criteria. There is no doubt that the NFAs have propelled organic solar cell technology to the efficiencies necessary for a viable commercial technology–but how far can they be pushed, and will they also deliver on equally important metrics such as stability?
Nonlinear optical (NLO) materials have attracted bounteous scientific attention in the modern era because of their optoelectronic and biological applications. In this respect, an attempt is made to present thermodynamically stable superalkali metals (Li 3 N, Li 3 O, Li 3 S and Li 3 F)-doped sumanene (C[Formula: see text]H[Formula: see text])-based complexes with fine NLO response properties. Nine isomers (I–III of Li 3 N@Sumanene, I–II of Li 3 O@Sumanene, I–II of Li 3 S@Sumanene and I–II of Li 3 F@Sumanene) are proposed, and their geometric, thermodynamic, electronic and NLO properties are explored by using density functional theory (DFT) calculations. Computational results reveal that the [Formula: see text] gap is reduced up to 0.56[Formula: see text]eV for doped complexes. The maximum hyperpolarizability response is calculated [Formula: see text][Formula: see text]a.u. for isomer II of the Li 3 F@Sumanene series. The participation of distinct fragments, type of interaction, and charge transfer are computed by the corresponding TDOS and PDOS, NCI and NBO analysis. For UV–Vis analysis and crucial excitation state, TD-DFT calculations are carried out, which exhibits that all doped complexes are transparent in the UV region. NCI analysis confirmed the Van-der Waals interactions as an important mode of adsorption between superalkalis and sumanene. This report provides an efficient superalkali doping technique for creating highly effective future NLO systems and recommends superalkali-doped sumanene systems as ideal NLO prospects for future NLO applications.
A series of four novel pi-conjugated chromophores named BDP1-BDP4 have been designed in quest to enhance the PCE of organic photovoltaic cells. These chromophores were developed by using 4,4-difluroboradiaza-s-indacene (BODIPY) as a core, Triphenylamine (TPA) as donor and different end-capped acceptors i.e., 2-ethylidene malononitrile (BDP1), methyl-2-cyanobut-2-enoate (BDP2), 4-ethylidene-2-methyl-5-thiooxoisothiazolidin-3-one (BDP3), 2-(2-ethylidene-5,6-difluoro-3-oxo-2,3-dihydroinden-1-ylidene) malononitrile (BDP4). DFT and TD-DFT approach using B3LYP functional was employed to assess the photophysical, as well as opto-electronic properties of designed chromophores BDP1-BDP4. FMOs and Transition Density Matrix evaluations were executed to get insights about charge distribution, chemical reactivity, and stability of all molecules under investigation. Exciton binding energy and reorganization energy values have been computed to investigate exciton dissociation and charge carrier mobilities, respectively. All the newly developed molecules exhibit reduced band gap, red shift absorption bands, low exciton binding energy, small reorganization energy values and moderate Voc value in comparison to reference molecule which demonstrate that these newly developed molecules can be utilized as favorable photovoltaic materials. BDP4 considered to be promising acceptor molecule with highest λmax (883 nm), narrow band gap (1.22eV) and lowest λe value (0.01136). This theoretical and computational study revealed that the designed chromophores could be employed as efficient acceptors, in order to upsurge the quantum efficiency of organic photovoltaic devices.
In the present computational study, four new small molecule acceptors (SMAs), R1, R2, R3, and R4 were designed with an A2-D-A1-D-A2 configuration by replacing the terminal acceptor A2 in reference molecule BT-dIDT with some influential acceptor groups for the exploration of their optoelectronic characteristics. Designed chromophores consisted of BT unit as electron capturing core, named A1, while end-capped acceptor moieties were named as A2, which were linked via IDT (D) units. The designed molecules contained peripheral acceptor groups named, 2-methylene malononitrile (R1), methyl 2-cyanocrylate (R2), 3-methyl-2-thioxo-thiazolidin-4-one (R3), and 2-(3-methyl-4oxo-thiazolidin-2-ylidine) malononitrile (R4). TD-DFT and DFT approaches were utilized to compute all the optoelectronic parameters of the molecular structures. The effect of terminal acceptors on the energy gaps, charge transfer ability, absorption properties, dipole moment, etc., of the newly formulated molecules (R1-R4) along with the reference were evaluated. Amongst all the investigated molecules, R4 exhibited the least band gap (2.26 eV), with the highest absorption values in both the studied phases (gas and solvent), while R3 showed the lowest hole reorganization energy (0.0074eV), thus highest hole mobility, along with a large open-circuit voltage and fill factor. These outcomes revealed that these A2-D-A1-D-A2 type SMAs with some consequential terminal acceptor components form auspicious candidates for the effective photovoltaic potential of OSCs.
Four acceptor-donor-acceptor (A-D-A) type cyclopentadithiophene core based non-fullerene small acceptor molecules were designed with the objective to improve the proficiency of photovoltaic cells. A comprehensive density functional theory (DFT) analysis was done by employing B3LYP functional with 6–31G (d, p) basis set to study optoelectronic properties of R as well as M1-M4 molecules, while the time-dependent self-consistent field (TDSCF) was utilized to analyze their excited state calculations. Several essential characteristics must be refined in order to enhance the efficiency of small molecular acceptors, i.e., density of states (DOS), HOMO-LUMO band gap, transition density matrix (TDM), dipole moment, reorganization energy, light harvesting efficiency, and open circuit voltage, etc. In comparison to the R molecule, all the derived molecules show better maximum absorption (in chloroform solvent) with a range of 886–951 nm and a smaller band gap with a range of 1.65–1.55 eV M2 retains the least exciton binding energy of 0.24 eV, and amongst all the investigated molecules M3 molecule has the least interaction coefficient values so, it possesses better charge transport probability. The reorganization energy values in eV for both electron (0.00579) and hole (0.00737) are the least for M3 molecule, so this molecule exhibits better charge mobility for electron and hole. VOC of R and M1-M4 molecule was calculated by theoretically computing the values of their complexes with PTB7-Th donor molecule.
This research project focuses on quantum chemical study of triphenyl diamine based molecules and DFT analysis of reference XSln847 and nine designed molecules to boost the efficiencies of organic solar cells and to make viable competitive solar cell. To study photovoltaic features, computational DFT and TD-DFT simulations are used to conduct extensive research at the molecular level of the investigated compounds. CAM-B3LYP/6-31G (d, p) level has been used to perceive molecules analytically for their predicted values of absorption maximum, highest light harvesting efficiency, frontier molecular orbitals and quantum chemical parameters i.e. chemical potential, chemical softness, chemical hardness, and electrophilicity index. Amongst TPDM-1 to TPDM-9 structures, TPDM-9 shows maximum absorption (530 nm) and lowest bandgap (3.19 eV). TPDM-7 has highest power conversion efficiency. While TPDM-4 shows better light harvesting efficiency to enhance organic solar cells efficiency. After successfully verifying the compatibility of the donor and acceptor interfaces, the PTB7-Th (donor) is used for electrophilic designed molecules while for donor designed molecules PC16BM (acceptor) is used as their HOMO LUMO values for the estimation of Voc values. All the proposed molecules show computationally amplified metrics, which is a compelling argument for their potential experimental use in creating effective solar cells.
In this study, five novel push-pull acceptor molecules with A-B-D-B-A arrangement have been formulated in the quest to boost the organic solar cells (OSCs), with respect to their electrical, optical, and chemical characteristics. Substitution of end-capped acceptor moieties in non-fullerene materials is an effective approach of molecular modeling, which finely tunes the optoelectronic properties of OSCs. The newly altered molecules (Y1-Y5) were flanked with different electron withdrawing units carrying indacenodithiophene (IDT) as the central electron donating core. The density functional theory (DFT) and time-dependent density functional theory (TD-DFT) analysis were carried out at B3LYP functional with 6-31G (d,p) basis set to investigate the geometrical and optical parameters such as quantum mechanical descriptors, light harvesting efficiency, ionization potential energy, absorption properties, electron affinity, dipole moment, molecular electrostatic potential, transition density matrix, the density of states, and reorganization energies. All of these studied molecules revealed greater electronic transitions, superior optical properties, fast charge mobilities, and better solubility in the polar solvent when compared to the reference molecule. Amongst all these derived molecules, Y1 emerged as a distinctive candidate, exhibiting the highest maximum absorption wavelength (884nm) in chloroform along with the smallest energy gap (1.72eV) as well as the lowest optical gap (1.40eV). Moreover, it has the highest electron affinity and ionization potential energy, least interaction coefficient, exciton binding energy, and reorganization energy (λe = 0.00340eV), which can be ascribed to its potent electron withdrawing moieties, which intensifies the transfer of charge between the donor and acceptor units within a molecule. We expect these modifications in the terminal groups around the central core to provide strong theoretical strategies to construct and amplify the photovoltaic parameters of OSCs in the future.
The influences triggered by the structurally diverse electron-withdrawing terminal group and fuse-ring electron-deficient core on the performance of NFAs OSCs are comprehensively investigated by using DFT, TD-DFT and Marcus charge transfer theory.
Nine new donor molecules BCi (i=1-9) of type D-π-A-π-D are explored to study their application to improve the efficiency of OSCs. These designed molecules contain a central diketopyrrolopyrrole acceptor linked to two terminal benzocarbazole donors by different π-bridges. Using density functional theory (DFT) and time-dependent DFT (TD-DFT) methods, various parameters like FMO, NBO, DOS analysis, absorption maxima, and ICT parameters have been estimated to evaluate the performance of newly designed molecules. Our investigations reveal that the modification of the π-bridges has a great effect on the optoelectronic and photovoltaic properties of the compounds. In this regard, it should be noted that the donor molecule BC6 with the π-spacer moiety thiazolothiazole exhibits a narrow band gap, a broad absorption spectrum, a better LHE, a lower values for λtot, ΔEL-L and chemical parameters, an acceptable Voc and a higher value of EA. Thus, they can be utilized as an electron-donating in photovoltaic applications.
Considering the worth of molecular designing, A-D-A type four small donor (SM1-SM4) photoactive materials comprised of DTS core, substituted with push-pull acceptors at terminal sites linked through bithiophene units were investigated. In present project, detailed theoretical consideration under DFT and TD-DFT methods (CAM functional/basis set 6-31G) was given-to explore wavelength dependent (absorption maxima, first excitation energy, light harvesting efficiency), electronic (FMO, DOS, TDM), reactivity (IP, EA, MEP), and charge transfer parameters (Voc, FF) of selected molecules (SM1-SM4) in systematic way. All novel molecules revealed broadening of absorption maxima and lessening of band gaps comparative to absorption coefficient and energy difference between HOMO/LUMO of RM due to electron pulling nature of acceptor groups. Greater dipole moment of all designed chromophores in excited state suggests their good solubility in solvent medium (chloroform) as compared to gaseous medium. Furthermore, charge transfer dynamics in terms of internal hole and electron reorganization energies give lower values which indicate higher transfer abilities for SM2 and SM1 respectively. Excellent output results for modelled molecules interpreted through open circuit voltage (with PC61BM) and fill factor, predict rise in PCE value than already reported molecule. Out of class, SM4 molecule emerged as an ideal photovoltaic material on account of better optical properties, easy electronic transitions, enhanced chemical reactivity, fast charge conductivity, and high estimated PCE. Eventually, these encouraging results favors the structural modeling of small molecules achieved through effective combination of end-capped moieties. We look forward that this entire work may provide strong theoretical guidelines, aids in designing and amplifying the optoelectronic features of proposed frameworks on vast scale than reference.
This research is carried out to investigate photovoltaic characteristics of the six modified molecules derived from benzothiadiazole core-based reference molecule JY5, using four different non-fullerene acceptors at ωB97XD/6-31G** via TD-DFT approach. To check the efficiency of these designed molecules dipole moment, band gap, binding energy, chemical-potential, soft and hard character, electrophilicity, light harvesting efficiency, open circuit voltage and fill factor are studied along with transition density matrix, molecular electro-potential surface, density of states and photoinduced electron transfer (PET). Amidst JY5-W1 to JY5-W6 structures, JY5-W4 molecule shows a broad absorption range with a λmax of 458 nm. JY5-W3 and JY5-W4 molecules shows the highest electron mobilities. The outstanding light harvesting efficiencies (>0.90) make the designed molecules a good candidate for organic solar cells. HOMO-LUMO gaps parameterize Voc as a key factor in evaluating photovoltaic outcome of designed molecules (electrophilic in nature) so, PTB7-Th is considered as a preferred donor as its lower HOMO (−5.01 eV) and higher LUMO level (−2.60 eV) results in increased Voc predicting an efficient organic solar cell.
Non-fullerene organic solar cells (OSCs) deliver the highest efficiency gains overall in reported literature. Efforts are being made to refine efficacies and stabilities of organic solar cells through the designing of acceptor molecules that contain powerful electron-withdrawing groups. Here, we computed four acceptors (Y1-Y4) by end-capped alterations on reference R and optimize photophysical, optoelectronic and photovoltaic properties. Therefore, certain properties such as orientation of FMO’s, excitation and binding energy, open-circuit voltage (Voc), transition density matrix and reorganizational energy of hole and electron are observed in comparison with reference. The calculated molecular structures of Y1 and Y4 show a high red-shift, while that of Y2 and Y3 display slightly blue-shift, along with very fine excitation energies and high charge mobilities. All these molecules (Y1-Y4) and the reference R presents band-gaps as small as 1.5–2.5 eV, and considerable charge transfer potential. This theoretical system shows that end-capped acceptors alteration is quite remarkable to establish desired optoelectronic properties. Thus, Y1-Y4 are suggested to researchers aiming at the potential commercialization of highly efficient solar cells systems.
In current study, four novel (A2-Л-A1-D-A1-Л-A2) type molecules namely NIDCS1, NIDCS2, NIDCS3, and NIDCS4 having central donor core (1,4-dimethoxybenzene) and end-capped bis(2-(5-(4-(N-(2-ethylhexyl)1,8-naphthalimide)yl) acceptors linked via thiophene spacer have been designed. Frontier molecular orbitals, UV-vis spectrum, density of states, transition density matrix, and reorganizational energies (RE) have been evaluated through density functional theory via CAM-B3LYP/6-31G** level of theory to find best candidate for photovoltaic applications. Among all designed molecules NIDCS3 is superior because of high maximum absorption value (454 nm), low energy gap (2.56 eV), high hole mobility (0.007408), and comparable open-circuit voltage as compared to reference molecule. Moreover, the combination of PC61BM/NIDCS3 molecule has been examined for efficient charge transfer which indicates that our investigated molecules act as donor material for high-performance organic solar cell. All designed molecules have shown the enhanced afore-said parameters that is plausible reason for their potential use in contriving the future proficient OSCs.
In recent epochs, the researchers are exploring for boost in the opto-electronic properties of active materials fabricated in Organic solar cell (OSCs). Herein, the eminent molecule Subphthalocyanines (SubPcs) is picked up as a reference molecule (R) and designed four 3D novel molecules by attaching electron withdrawing (EW) groups at six peripheral positions of R, giving them identity; M1, M2, M3, and M4. These 3D non-fullerene acceptors are theoretically analysed for UV-Vis absorption, frontier molecular orbitals (FMOs), density of states (DOS), Transition density matrix (TDM), internal molecular reorganization energy, the binding energy, and interaction with renowned donor PTB7-Th. Comparative to molar absorption and HOMO/LUMO band gap of R (λ max = 650.2 nm and Eg = 1.633 eV), novel acceptors has better results i.e., λ max ranges from 733-801.5 nm and Eg ranges from 1.088-1.438 eV. While, the hole reorganization energy (i.e., in range of 0.111773-0.33002) and binding energies (i.e., 0.170-0.252) of all novel molecules is noticed lower comparative to R (λh = 0.178402 and Eb = 0.277, respectively). Exceptionally, M3 is prompted as promising light harvesting material with better molar absorption (λ max = 975.0 nm), lower band gap (Eg = 1.088 eV), less hole reorganization energy (λh = 0.033002 eV) and lower binding energy (0.182). Due to exceptional properties of M3 comparative to other designed acceptor molecules, it is analysed with donor PTB7-Th as donor/acceptor interface. Ultimately, it is proved to be efficient interface due to better charge transition. Meanwhile, all designing 3D acceptors are more efficient than R with exceptionally better opto-electronic properties of M3.
In this work, we fabricate, characterize and present a stability study of p-DTS(FBTTh2)2:PC70BM inverted organic solar cells (iOSCs) with two different solution-processed electron transport layers (ETLs), PFN and ZnO, under indoor light and AM 1.5 G illumination spectrum. A warm white color light-emitting diode was used as the indoor light source. Under the luminance of 1000 lux, a maximum power conversion efficiency (PCE) of 10.85% and maximum power density (MPP) of 45.1 μW/cm² were obtained for cells with PFN as ETL. After 1536 h of constant indoor light illumination, the PCE remained above 70% of the original value. The best stability of encapsulated devices, under AM 1.5 illumination spectrum was also observed for these cells, which still maintained a PCE above 60% after 6000 h.
The light harvesting and photocurrent generation from acceptors largely determine the photovoltaic performance of organic solar cells (OSCs). We have designed and prepared two medium band gap non-fullerene acceptors (NFAs),...
To extinguish the thirst of extraordinary tailback in the stock of energy and to jack up the operational effectiveness of organic solar cells, 5 new donor molecules namely BDTM1, BDTM2, BDTM3, BDTM4, BDTM5 have been designed by the structural tailoring of the already experimentally synthesized POBDT-4Cl. POBDT-4Cl is taken as a reference designated as BDTR. All the designed chromophores constitute benzodithiophene as donor and thiophene bridged end-capped (3-methyl-5-methylene-2-thioxothiazolidin-4-one) BDTM1, (2-methylenemalononitrile) BDTM2, (methyl 2-cyanoacrylate) BDTM3, (2-(3-methyl-5-methylene-4-oxothiazolidin-2-ylidene)malononitrile) BDTM4, (4-(5-methylthiophen-2-yl)benzo[c][1,2,5]thiadiazole) BDTM5 acceptor groups. Influence of different terminal acceptor moieties on the molecular orbitals, density of states (DOS), maximum absorption (λmax), energy required for the generation of electron and hole carrier, transition density matrix (TDM), dipole moment, reorganization energy (RE), and open-circuit voltage (VOC) has been inquired via density-functional theory (DFT) and time-dependent density functional theory (TDDFT) methodology using B3LYP/6-31G (d,p) and these afore-mentioned features of newly devised molecules have been compared with the reference (BDTR). Among all newly designed molecules (BDTM1-BDTM5), BDTM1 exhibited the highest λmax value of 725 nm. BDTM3, BDTM4, and BDTM5 have displayed the highest dipole moment than the reference (BDTR). Cation (hole) transport rate of BDTM5 (0.00578 eV) and BDTM2 (0.00632 eV) has been explored lower than BDTR (0.00662 eV). Similarly, BDTM5 has displayed lower anion (electron) transport rate (0.00578 eV) relative to BDTR (0.00603 eV). Among all designed molecules, BDTM5 has expressed formidable and unique results accompanied by the lowest band gap (1.90 eV), comparable λmax (720 nm), and VOC. All newly constructed molecules have exposed enhanced VOC. Briefly, the thiophene bridged end-capped acceptor modification approach has been demonstrated compelling in providing the door to plan profoundly effective photovoltaic materials accompanied by exquisite optoelectronic parameters.
The ambient stability and processability of organic solar cells (OSCs) are important factors for their commercialization. Herein, we selected four benzo[1,2-b:4,5-b']difuran (BDF) polymers and two electron acceptors to examine the role of photovoltaic materials in the ambient stability. The investigations revealed that the MoO
x
layer is the detrimental factor for the ambient stabilities. The penetration of MoO
x
into the active layer and their interactions will strengthen the interface and form a favorable contact, hence leading to the increased photovoltaic performance, in which the efficiency loss induced by air was balanced out. As such, these BDF polymer-based non-fullerene (NF) OSCs possessed very promising ambient stabilities even after ∼1000 h with the almost maintained power conversion efficiencies (PCEs). These results drive us to further investigate the ambient processability of these NF-OSCs. The PCEs from the devices processed under ambient condition only possessed 0.3-2% loss compared to those devices under inert conditions, which suggest the significant potentials of BDF polymers to develop highly efficient and stable NF-OSCs for the practical applications.
End‐capped acceptors modification of fused ring electron acceptors (FREAs) is an attractive strategy to boost the optoelectronic and photovoltaic properties of the materials. FREAs are also proven beneficial due to their tremendous applications in organic solar cells (OSCs). Among fused‐ring electronic species, small fullerene‐free FREAs have already been drawn more attention due to their near‐infrared sensitivity and constantly increasing efficiencies. Therefore, we have designed six new FREAs (K1–K6) having selenophene as π‐bridge in between the central alkylated indaceno[1,2‐b:5,6b]dithiophene (IDT) unit after the incorporations of various end‐capped acceptors on to the recently synthesized IDT2SeC2C4‐4F molecule. Structural–property relationship and photophysical and photovoltaic properties of newly designed molecules are studied with the help of density functional theory (DFT) and time‐dependent DFT (TD‐DFT). Certain critical specifications like frontier molecular orbitals (FMOs) alignment, density of states (DOS), absorption maxima, excitation energy, binding energy (BE) along with transition density matrix (TDM), and the specifically estimated reorganizational energy values of electron and hole and the open circuit voltages of newly designed molecules are computed and compared with reference molecule. Generally, a red‐shifting absorption behavior of FREAs is considered the most important reason for their high efficiencies in OSCs. Our novel designed molecules exhibit red shift in absorption spectrum. Similarly, low excitation and binding energies of designed molecules offer improved power conversion efficiencies (PCEs) with highest possible charge photocurrent density (Jsc) in OSCs devices. Furthermore, study of PTB7‐Th/K1 complex is also done in order to examine charge transfer between within complex. By introducing the efficient end‐capped acceptor moieties in reference molecule, enhancement in charge mobilities is noted. The large open circuit voltage, low reorganizational energies, narrower highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) energy gap, lower binding and excitation energies, and highly red shifting in absorption phenomenon indicate an efficient designing of molecules, which could be best fitted for high efficiency OSCs. Finally, theorized molecules are much superior related to their photovoltaic and electronic properties and thus are recommended to experimentalist for their synthesis and out‐looking future developments of highly efficient solar cells devices. We have designed six new FREAs (K1‐K6) having selenophene π‐bridge between central alkylated indaceno[1,2‐b:5,6b]dithiophene (IDT) unit after end‐capped acceptors modification of recently synthesized IDT2SeC2C4‐4F molecule. Structural‐property relationship, photophysical and photovoltaic properties of newly designed molecules are studied with the help of density functional theory and time dependent‐density functional theory and found better than synthesized molecule. Designed molecules are recommended for high performance organic solar cells.
The development of organic photovoltaic (OPV) cells has long been guided by the idea that excitons – bound electron-hole pairs created by light absorption – diffuse only 5-10 nm. True for many materials, this constraint led to an inherently complex device architecture – the bulk heterojunction – that has obscured our understanding of device physics, and handicapped rational material design. Here, we investigate the photophysics of a series of planar bilayer heterojunction devices incorporating fused-ring electron acceptors with power conversion efficiencies up to 11%. Using ultrafast optical spectroscopy, we demonstrate the importance of long-range layer-to-layer energy transfer in planar structures, isolating this effect by including an insulating layer between the donor and acceptor layers to eliminate charge transfer effects. We show that the slab geometry facilitates substantially longer-range energy transfer than between isolated molecules or small domains. Along with high molecular packing densities, high absorption coefficients, and long exciton diffusion lengths, we show that these effects amount to exciton harvesting length scales that match the light absorption lengths and thereby enable efficient bilayer devices. Our quantitative analysis of bilayer structures also accounts for large domain sizes in bulk-heterojunction devices including fused-ring electron acceptors, and it quantifies the importance of strong resonant spectral overlap is for material selection and design for highly efficient OPVs.
Polymer solar cells based on fullerene acceptors have reached in recent years power conversion efficiencies (PCEs) approaching 13%. The advent of non-fullerene acceptors (NFAs) with the advantages of synthetic versatility, a strong absorption ability and high thermal stability has resulted in impressive PCEs of over 18% in single junction devices. The insertion of interlayers between the active components and electrodes plays a key role in charge collection, boosts the efficiency and improves the device stability. However, the mechanisms regulating the interaction between interlayer materials and active layers based on NFAs are not yet completely rationalized. This review article summarizes organic, inorganic and hybrid materials used as anode and cathode interlayers in conventional and inverted fullerene-free solar cells. Particular attention is paid to the distinctive features of the interlayers when used in non-fullerene solar cells. We will also comment on the fabrication processes with an emphasis on the transition from small area, lab devices to large area modules and on possible mechanisms which are behind.
A series of random donor-acceptor conjugated polymers with naphthalene diimide and thiophene units were designed and synthesized with varying difluorothiophene (FTh) substitution. In comparison with the non-fluorinated polymer F0, FTh-containing random polymers exhibit increased molecular interaction in solution state as well as enhanced solid state ordering. However, higher FTh content leads to unfavorable decrease in polymer solubility. When incorporated into all-polymer solar cells (all-PSCs) using PT8 as the donor, the crystallinity between donor and acceptor polymer was optimized using random copolymer strategy, and a best PCE of 9.04% was achieved with 10% FTh substitution, which is among the highest reports of wide bandgap all-PSCs. We believe that these findings will further provide insight into the control of polymer-polymer blend with desirable optoelectronic properties.