In this study, we investigate the underlying origin of the high performance of PM6:Y6 organic solar cells. Employing transient optoelectronic and photoemission spectroscopies, we find that this blend ...exhibits greatly suppressed charge trapping into electronic intra-bandgap tail states compared to other polymer/non-fullerene acceptor solar cells, attributed to lower energetic disorder. The presence of tail states is a key source of energetic loss in most organic solar cells, as charge carriers relax into these states, reducing the quasi-Fermi level splitting and therefore device
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. DFT and Raman analyses indicate this suppression of tail state energetics disorder could be associated with a higher degree of conformational rigidity and uniformity for the Y6 acceptor. We attribute the origin of such conformational rigidity and uniformity of Y6 to the presence of the two alkyl side chains on the outer core that restricts end-group rotation by acting as a conformation locker. The resultant enhanced carrier dynamics and suppressed charge carrier trapping are proposed to be a key factor behind the high performance of this blend. Low energetic disorder is suggested to be a key factor enabling reasonably efficient charge generation in this low energy offset system. In the absence of either energetic disorder or a significant electronic energy offset, it is argued that charge separation in this system is primarily entropy driven. Nevertheless, photocurrent generation is still limited by slow hole transfer from Y6 to PM6, suggesting pathways for further efficiency improvement.
In this study, we investigate the underlying origin of the high performance of PM6:Y6 organic solar cells.
High‐performance ternary organic solar cells are fabricated by using a wide‐bandgap polymer donor (bithienyl‐benzodithiophene‐alt‐fluorobenzotriazole copolymer, J52) and two well‐miscible ...nonfullerene acceptors, methyl‐modified nonfullerene acceptor (IT‐M) and 2,2′‐((2Z,2′Z)‐((5,5′‐(4,4,9,9‐tetrakis(4‐hexylphenyl)‐4,9‐dihydros‐indaceno1,2‐b:5,6‐b′dithiophene‐2,7‐diyl)bis(4‐((2‐ethylhexyl)oxy)thiophene‐5,2‐diyl))bis(methanylylidene))bis(3‐oxo‐2,3‐dihydro‐1H‐indene‐2,1‐diylidene))dimalononitrile (IEICO). The two acceptors with complementary absorption spectra and similar lowest unoccupied molecular orbital levels show excellent compatibility in the blend due to their very similar chemical structures. Consequently, the obtained ternary organic solar cells (OSC) exhibits a high efficiency of 11.1%, with an enhanced short‐circuit current density of 19.7 mA cm−2 and a fill factor of 0.668. In this ternary system, broadened absorption, similar output voltages, and compatible morphology are achieved simultaneously, demonstrating a promising strategy to further improve the performance of ternary OSCs.
Ternary organic solar cells show over 11% power conversion efficiency by using two compatible nonfullerene acceptors with complementary absorption spectra, similar chemical structures, and similar lowest unoccupied molecular orbital levels. Broadened absorption, similar output voltages, and compatible morphology are achieved simultaneously, demonstrating a promising strategy to improve the performance of OSCs.
Reducing non-radiative charge recombination is of critical importance to achieving high-performance organic photovoltaic (OPV) cells. The correlation between the exciton behaviors and non-radiative ...charge recombination is rarely studied. In this work, we achieved an increase in the exciton diffusion length (LD) in the acceptor phase via introducing HDO-4Cl to the PBDB-TF:eC9-based system. Compared with the eC9-based film, the exciton LD in the HDO-4Cl:eC9-based film is increased from 12.2 to 16.3 nm. The enlarged exciton LD can obviously decrease the non-radiative charge recombination and increase the efficiency of photon utilization in the PBDB-TF:eC9-based OPV cell. Finally, we not only obtained an outstanding power conversion efficiency (PCE) of 18.86% but also demonstrated the correlations between the non-radiative energy loss and exciton behaviors. The results show that regulating the exciton behaviors is an effective way to reduce the non-radiative energy loss and realize high-efficiency OPV cells.
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•Correlations between non-radiative energy loss and exciton behaviors are revealed•The exciton-diffusion length can be effectively enlarged through ternary strategy•A high PCE approaching 19% is demonstrated
Organic photovoltaic (OPV) cells have recently emerged as cost-effective and energy-efficient candidates of green energy sources. Further improvement in power conversion efficiency (PCE) is still needed for practical application. Compared with the inorganic photovoltaic cells, the non-radiative energy loss (Eloss, non-rad) in OPV cell is relatively large. Therefore, reducing the Eloss, non-rad is an effective way to achieve a breakthrough in the PCE of OPV cells. In addition to material synthesis and morphology optimization, optimizing exciton behaviors is also crucial to reduce the Eloss, non-rad and, thus, enhance the state-of-art high-performance OPV cells. In this work, the exciton diffusion length in PBDB-TF:eC9-based active layer is effectively enhanced through introducing a third component named HDO-4Cl. As a result, we not only achieved an outstanding PCE of approaching 19% but also revealed the correlations between the Eloss, non-rad and exciton behaviors.
Suppressing the non-radiative energy loss by optimizing the exciton behaviors in PBDB-TF:eC9-based organic photovoltaic (OPV) cells is demonstrated in this work. The exciton diffusion length and exciton lifetime in the active layer based on PBDB-TF:eC9 are enhanced via introducing HDO-4Cl, resulting in the obvious reduction in the non-radiative charge recombination in the corresponding OPV cell. As a result, a high PCE of 18.86% is achieved in the single-junction OPV cell.
At present, most of state‐of‐the‐art power conversion efficiencies (PCEs) of organic solar cells (OSCs) are achieved from the photoactive materials involving donor–acceptor (D–A) copolymer donors. It ...is well known that the complicated molecular structure of D–A copolymers means the tedious synthesis, which brings about severe cost issue and poor scalability for the industrial production. Therefore, to develop application‐oriented OSCs, considerable attention should be paid on simplifying the chemical structures of polymer donors. Polythiophene (PT) and poly(thiophene vinylene) (PTV) derivatives should be among the simplest polymer donors, and OSCs based on them have made some breakthroughs in past 2 years. Here, we briefly introduce the recent advances of OSCs based on low‐cost polymers including poly(3‐hexylthiophene) (P3HT), PT derivatives, and PTV derivatives, respectively, and emphasize the importance of modulating energy levels, preaggregation effect, and D/A miscibility for the past progress as well as the future development. At last, we also propose some challenges demanding prompt solution for realizing practical application of OSCs, aiming at providing guidance and stimulating new ideas for further research.
Low‐cost polymer donors like P3HT, polythiophene derivatives and poly(thiophene vinylene) derivatives exhibit great potential for realizing practical application of organic solar cells (OSCs). This review introduces the recent advances of OSCs based on these low‐cost materials and proposes optimization principles as well as challenges for further development toward application.
A series of bay-linked perylene bisimides as non-fullerene acceptors for organic solar cells are designed. The best power conversion efficiency up to 3.63% based on s-diPBI (1b) is demonstrated by ...fine-tuning optoelectronic properties resulting from different degrees of twisting and flexibility by bay-linkages.
In this Letter, we highlight a system with a well-known polymer donor (PTB7-Th) blended with a narrow band gap nonfullerene acceptor (IEICO-4F) as the active layer and 1-chloronaphthalene (CN) as the ...solvent additive. Optimization of the photoactive layer nanomorphology yields a short-circuit current density value of 27.3 mA/cm2, one of the highest values in organic solar cells reported to date, which competes with other types of solution-processed solar cells such as perovskite or quantum dot devices. Along with decent open-circuit voltage (0.71 V) and fill factor values (66%), a power conversion efficiency of 12.8% is achieved for the champion devices. Morphology characterizations elucidate that the origin of this high photocurrent is mainly the increased π–π coherence length of the acceptor, the domain spacing, as well as the mean-square composition variation of the blend. Optoelectronic measurements confirm a balanced hole and electron mobility and reduced trap-assisted recombination for the best devices.
A new conjugated polymer based on 5,7-bis(2-ethylhexyl)benzo1,2-c:4,5-c′dithiophene-4,8-dione, named as PBDTBDD, was designed, synthesized, and applied in polymer solar cells (PSCs). A power ...conversion efficiency (PCE) of 6.67% was obtained from the PBDTBDD/PC61BM-based PSC, which is a remarkable result for the PSCs using PC61BM as electron acceptor. The PBDTBDD/PC61BM-based device exhibits a narrow absorption band and excellent quantum efficiency in the range from 500 to 700 nm. Furthermore, PBDTBDD shows a strong aggregation effect in solution state, and the study indicates that although the temperature used in solution preparation has little influence on molecular orientation as well as crystallinity of the D/A blend, it plays an important role in forming proper domain size in the blend. This work provides a good example to reveal the correlation between the morphology of the blend films and the processing temperature of the solution preparation. Furthermore, the study in this work suggests an interesting and feasible approach to modulate domain size without changing crystallinity of the blend films in PSCs.
Attaching meta‐alkoxy‐phenyl groups as conjugated side chains is an easy and effective way to modulate the molecular energy level of D‐A polymer for photovoltaic application, and the polymer solar ...cells based on the polymer consisting meta‐alkoxy‐phenyl groups as conjugated side chain, PBT‐OP, shows an enhanced open circuit voltage and thus higher efficiency of 7.50%, under the illumination of AM 1.5G, 100 mW/cm2.
For the PDPP3T/PCBM system investigated here, atomic force microscopy, resonant soft X‐ray scattering, and grazing incidence wide angle X‐ray scattering are used as an initial set of tools to ...determine the surface texture, the bulk compositional morphology, and the crystallization behavior, respectively. We find systematic variations and relate them to device performance. A solvent mixture of DCB/CF/DIO = 76:19:5 (v/v/v) yields a PCE of 6.71%.
Halogenation is a very efficient chemical modification method to tune the molecular energy levels, absorption spectra and molecular packing of organic semiconductors. Recently, in the field of ...organic solar cells (OSCs), both fluorine- and chlorinesubstituted photovoltaic materials, including donors and acceptors, demonstrated their great potentials in achieving high power conversion efficiencies (PCEs), raising a question that how to make a decision between fluorination and chlorination when designing materials. Herein, we systemically studied the impact of fluorination and chlorination on the properties of resulting donors (PBDB-T-2F and PBDB-T-2Cl) and acceptors (IT-4F and IT-4Cl). The results suggest that all the OSCs based on different donor and acceptor combinations can deliver good PCEs around 13%–14%. Chlorination is more effective than fluorination in downshifting the molecular energy levels and broadening the absorption spectra. The influence of chlorination and fluorination on the crystallinity of the resulting materials is dependent on their introduction positions. As chlorination has the advantage of easy synthesis, it is more attractive in designing low-cost photovoltaic materials and therefore may have more potential in largescale applications.
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