Wang Wei, Li Gongchun, Li Yuhao, Zhan Chun, Lu Xinhui, Xiao Shengqiang
State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology Wuhan 430070 P. R. China
Department of Physics, The Chinese University of Hong Kong Sha Tin Hong Kong SAR 999077 P. R. China
RSC Adv. 2021 Sep 28;11(51):31992-31999. doi: 10.1039/d1ra05426k. eCollection 2021 Sep 27.
As an ending acceptor unit (A) within acceptor-donor-acceptor (A-D-A)-type small molecule acceptors (SMAs), monobrominated 1,1-dicyanomethylene-3-indanone (IC-Br) plays a critical role on developing high-performance SMAs and polymer acceptors from polymerizing SMAs. IC-Br is usually a mixture (IC-Br-m) consisting of positional isomeric IC-Br-γ and IC-Br-δ (bromine substituted on the γ and δ positions, respectively). The positional isomeric effect of these monobrominated ending groups has been witnessed to take an important role on regulating the photovoltaic performance. Fully investigating this isomeric effect of monobromination would be of great value for SMAs and even polymer acceptors. In this study, benefitting from the separation of IC-Br-γ and IC-Br-δ from IC-Br-m with high yields, bis(thieno[3,2-]cyclopenta)benzo[1,2-:4,5-']diselenophene (BDSeT) was chosen as the D unit and combined with IC-Br-γ, IC-Br-δ and IC-Br-m as A units, respectively. Three A-D-A type SMAs (BDSeTICBr-γ, BDSeTICBr-δ and BDSeTICBr-m) have thus been obtained. When blended with the representative donor polymer of PBDB-T-2Cl to construct bulk heterojunction (BHJ) polymer solar cells (PSCs), BDSeTICBr-γ, BDSeTICBr-δ and BDSeTICBr-m devices offered power conversion efficiencies (PCEs) of 9.42, 10.63, and 11.54% respectively. The result indicated the superior photovoltaic performance of the isomer mixture over the pure isomers, which was contrary to the reported ones that the pure isomers of SMAs used to give a better performance. The superior performance of the BDSeTICBr-m devices was mainly reflected in the improved carrier generation and transport as well as the carrier recombination suppression. In the three PBDB-T-2Cl:SMA BHJ films, a comparable intermixing phase and acceptor domain sizes were observed. Compared with BDSeTICBr-γ and BDSeTICBr-δ, BDSeTICBr-m showed a preferential face-on orientated packing with the closest π-π stacking in its BHJ film, probably accounting for its higher photovoltaic performance than those of the pure isomers. This study provides an alternative sight to develop efficient SMAs with suitably monobrominated IC ending groups for the strategy of polymerizing SMAs.
作为给体-受体-给体（A-D-A）型小分子受体（SMA）中的末端受体单元（A），单溴代1,1-二氰基亚甲基-3-茚满酮（IC-Br）在开发高性能SMA以及由SMA聚合得到的聚合物受体方面起着关键作用。IC-Br通常是一种混合物（IC-Br-m），由位置异构体IC-Br-γ和IC-Br-δ组成（溴分别取代在γ和δ位置）。已证实这些单溴代末端基团的位置异构效应在调节光伏性能方面发挥着重要作用。全面研究这种单溴代的异构效应对于SMA乃至聚合物受体都具有重要价值。在本研究中，得益于从IC-Br-m中高产率地分离出IC-Br-γ和IC-Br-δ，双（噻吩并[3,2-]环戊烯）苯并[1,2-:4,5-']二硒吩（BDSeT）被选作给体单元（D），并分别与IC-Br-γ、IC-Br-δ和IC-Br-m作为受体单元（A）相结合。由此得到了三种A-D-A型SMA（BDSeTICBr-γ、BDSeTICBr-δ和BDSeTICBr-m）。当与代表性给体聚合物PBDB-T-2Cl共混以构建体相异质结（BHJ）聚合物太阳能电池（PSC）时，BDSeTICBr-γ、BDSeTICBr-δ和BDSeTICBr-m器件的功率转换效率（PCE）分别为9.42%、10.63%和11.54%。结果表明异构体混合物的光伏性能优于纯异构体，这与报道的SMA纯异构体通常表现出更好性能的情况相反。BDSeTICBr-m器件的优异性能主要体现在载流子产生和传输的改善以及载流子复合的抑制上。在三种PBDB-T-2Cl:SMA BHJ薄膜中，观察到了相当的混合相和受体域尺寸。与BDSeTICBr-γ和BDSeTICBr-δ相比，BDSeTICBr-m在其BHJ薄膜中表现出优先的面取向堆积以及最紧密的π-π堆积，这可能是其光伏性能高于纯异构体的原因。本研究为通过合适的单溴代IC末端基团开发高效SMA以用于SMA聚合策略提供了一个新的视角。
