Ternary strategy: An analogue as third component reduces the energy loss and improves the efficiency of polymer solar cells

Ternary strategy is a convenient and effective method to boost the performance of polymer solar cells(PSCs).Utilizing a ternary strategy to trade-off between the energy loss and the efficiency of devices however requires further exploration.Here,through the hydroxyl(-OH)and acetoxy(-OCOMe)substitution atβ-position of the IC terminal group,we developed two new synthetic acceptors,BTIC-OH-βand BTICOCOMe-β,which were designed to confine the morphology aggregation.Introduction of an analogue as the third component provides a simple but efficient way to further balance the short current density(Jsc)and open-circuit voltage(Voc),leading to a champion efficiency based on PBDB-T:PBDB-TF:BTIC-OCOMe-β,effectively as high as 12.45%.The results were examined mainly in terms of the morphology characterization,electroluminescence external quantum efficiency(EQEEL),steady-state photoluminescence(PL)and transient technology.It suggested fine-tuning of the morphology by ratio modulation,reduction of the energy loss,construction of a promising pathway for charge transfer in the ternary system and enhancing the carrier extraction.In this way,a ternary strategy with an analogue donor could provide more routes to higher-quality solar cells.

Crystallography,Packing Mode,and Aggregation State of Chlorinated Isomers for Efficient Organic Solar Cells

Revealing the molecular packing,intermolecular interactions,and aggregation behaviors in the nanocrystalline bulk heterojunction(BHJ)domains undertake the tasks for future materials design for efficient solar cells,especially in understanding the structure–property relationship of isomeric non-fullerene acceptors(NFAs).Theoretical calculations reveal that 2ClIC-βδ,withβ-andδ-chlorine-substituted terminal groups,achieves a relatively higher dipole moment for enhanced intermolecular interactions.More importantly,when comparing the single-crystal X-ray diffraction patterns of three isomeric NFAs,BTIC-BO4Cl-βδ,BTIC-BO4Cl-βγ,and BTIC-BO4Cl,the synergistic effect of chlorine atoms at theβ-andδ-positions endows BTIC-BO4Cl-βδbetter molecular planarity with a dihedral angle of 1.14°.In turn,this creates the shortestπ∙∙∙πdistance(3.28Å)and smallest binding energies(−51.66 kcal mol^(−1))of the three NFAs,resulting in the tightest three-dimensional network packing structure with a framework of L_(x)=14.0Åand L_(y)=13.6Å.Such a structure has multiple intermolecular interactions for better charge transfer.However,the chlorine atomat theγ-position in the other two isomers contributes to non-intermolecular interactions with subordinate packing arrangements.Subsequently,the red-shifted UV-absorption and higher electron mobility observed in neat films of BTIC-BO4Cl-βδagree well with its more ordered crystallinity.This leads to a more suitable fiber-like phase separation in the corresponding active blend,ultimately improving the device performance with superior charge transport.As a result,the highest power conversion efficiency of 17.04%with a current density of 26.07 mA cm^(−2)was obtained with the BTIC-BO4Cl-βδ-based device.The carrier dynamics test and grazing incidence wide-angle X-ray scattering measurement indicate that the packing arrangement of molecules in the nanocrystalline BHJ domains is consistent with their crystallinity.This work investigates the structure–property differences in three acceptors and emphasizes the effect of isomeric chlorine substitution,which suggests that changes in the crystal packing arrangement,especially the size of the framework,have a considerable influence on charge carrier transport and ultimately are reflected on the device efficiency elevation.

Near-Infrared All-Fused-Ring Nonfullerene Acceptors Achieving an Optimal Efficiency-Cost-Stability Balance in Organic Solar Cells

Synergistically achieving stability,cost,and efficiency is crucial for the commercialization of organic solar cells(OSCs).Despite the rapid development of 2-(3-oxo-2,3-dihydro-1H-inden-1-ylidene)malo nonitriletypenon fullerene acceptors(NFAs),they areinherently unstable due to the vulnerable exocyclic double bond and possess high synthesis complexity(SC).Based on the“all-fused-ring electron acceptor(AFAR)”concept,we report two new near-infrared NFAs,F11 and F13,featuring all fused dodecacyclic rings.By developing a whole set of synthetic procedures,F11 and F13 can be conveniently prepared at a 10 g scale within a notably short period,displaying both the low SC and the lowest costs among reported NFAs,even comparable to the classical photovoltaic material,P3HT.In comparison with the one-dimensional stacking of ITYM(ITYM=2,2′-(7,7,15,15-tetrahexyl-7,15-dihydro-s-indaceno[1,2-b:5,6-b′]diindeno[1,2-d]thiophene-2,10(2H)-diylidene)dimalononitrile),the first AFRA,and mixed J-and H-aggregations in Y6,F-acceptors show a compact honeycomb-type three-dimensional stacking with exclusive J-aggregations,favoring multichannel charge transport.By matching a medium-bandgap polymer donor,F13 delivers greater than 13%power conversion efficiencies,which is the highest performance among non-INCN acceptors,and shows device stability superior to the typical ITIC-and Y6-based OSCs as evidenced by the negligible burn-in losses.This work presents a first and successful example of NFAs achieving an optimal efficiency-cost-stability balance in OSCs.

单晶衍射技术在有机太阳能电池受体材料中的应用

有机太阳能电池器件的光电转化效率已超过18%.为了进一步推动其发展,有必要从原子层面上了解材料的堆积信息,来帮助设计和开发性能优异的受体分子.通过单晶X射线技术可观察到的分子在固态下的堆积排列方式和分子间的相互作用力,通常被用来指导设计具有预期物理化学性质的材料.本文主要讨论单晶X射线衍射技术在非富勒烯有机太阳能电池受体中的应用进展,着重强调受体材料结构设计、堆积排列和器件性能之间的关系.此外,我们发现了受体分子"三维网络堆积"的现象,对比了其在A-D-A体系和A-DAD-A体系中的不同,研究了其在氯取代、氟取代、溴取代和三氟甲基取代体系中的特性.对三维网络传输的理解可为高性能材料的设计提供指导,通过单晶分析理解和调整材料的聚集状态和分子间相互作用对开发新型受体具有重要意义.

Tuning the Molecular Weight of Chlorine-Substituted Polymer Donors for Small Energy Loss

The molecular weight of polymers plays a major role in their aggregation and miscibility in active layer,which eventually dominate the energy loss and device performance.A series of chlorine-substituted PBD-CI polymers with controlled molecular weight have been synthesized as templates to discern a relationship between molecular weight and the optical properties,energy levels,morphologies,energy loss and photovoltaic performance.Although it has similar optical and electrochemical properties,when blended with acceptor N3,the low molecular weight polymer PBD-CI_(L) gives the biggest energy loss value,and a PCE of 12.06%.PBD-CI_(H) shows a moderate energy loss,but displays the lowest PCE of 9.00%as a result of excessive aggregation.PBD-CI_(M) with a medium molecular weight gives the smallest energy loss and achieves a PCE of 17.17%,which is among one of the highest values recorded to date for the C卜substituted polymer solar cells.Moreover,the molecular weight mainly affects the nonradiative energy loss(△E_(3)), PBD-CI_(M) also shows the smallest value of 0.252 eV among three polymer donors.These results show the effect of controlling the molecular weight to achieve a small energy loss and provide guidelines which can lead to an understanding of the real photovoltaic performance of new materials.