Development of high-performance small-molecular acceptors (SMAs) and an eco-friendly and simple device fabrication procedure is very crucial for scalable production of polymer solar cells (PSCs) in the future. Here, we designed and synthesized two new nonacyclic SMAs (IPYT-IC and IPYT-ICF) featuring an A–DA′D–A-type molecular configuration, in which an electron-deficient 6,12-dihydro-diindolo[1,2-b:10,20-e]pyrazine (IPY) moiety was used as the additional acceptor unit (A′) and fused with the electron-rich diarylcyclopentadienylthiophene segment (D) to form a DA′D-type central core (IPYT), and 3-(dicyanomethylidene)indol-1-one (IC) or 5,6-difluoro-3-(dicyanomethylene)indol-1-one (ICF) acted as the terminal acceptor group (A). The rigid coplanar DA′D-type core containing a weakly electron-deficient IPY unit is beneficial to broaden the absorption range, improve light-harvesting ability, reduce the band gap, upshift the lowest unoccupied molecular orbital (LUMO) energy level, and enhance the charge transport of the resultant SMAs. Meanwhile, with respect to IPYT-IC, fluorinated IPYT-ICF exhibits a stronger absorption with a narrower band gap, higher electron mobility, and lower-lying highest occupied molecular orbital/LUMO energy levels. The as-cast PSCs based on IPYT-ICF using the polymer PTB7-Th as an electron donor achieve a power conversion efficiency of up to 7.00% with eco-friendly o-xylene (XY) as the processing solvent without any additive and post-treatment, which is higher than that of devices based on IPYT-IC (4.50%) mainly originating from the larger J_sc and FF because of the higher carrier mobilities, better charge transport and collection properties, weaker charge recombination, and superior film morphology. However, IPYT-IC-based devices present an outstanding V_oc of up to 0.98 V because the weakly electron-deficient A′ unit (IPY) upshifts LUMO levels of these SMAs. Our results illustrate that the weakly electron-deficient IPY can be a promising A′ unit to develop efficient A–DA′D–A-type SMAs for additive-free and eco-friendly as-cast PSCs.

中文翻译：

---

基于6,12-二氢-二吲哚并[1,2- b：10,20- e ]吡嗪单元的A-DA'D-A小分子受体的开发，可用于快速铸造聚合物太阳能电池

高性能小分子受体（SMA）的开发以及生态友好和简单的设备制造程序对于将来可扩展的聚合物太阳能电池（PSC）的生产至关重要。在这里，我们设计并合成了两种新的非环状SMA（IPYT-IC和IPYT-ICF），它们具有A–DA'D–A型分子构型，其中缺电子的6,12-二氢-二吲哚[1,2] - b：10,20- ê将]吡嗪（IPY）部分用作附加受体单元（A'），并与富含电子的二芳基环戊二烯基噻吩片段（D）融合形成DA'D型中央核（IPYT）和3-（二氰基亚甲基）吲哚-1-一（IC）或5，6-二氟-3-（二氰基亚甲基）吲哚-1-一（ICF）充当末端受体基团（A）。包含弱电子缺陷IPY单元的刚性共面DA'D型核有利于拓宽吸收范围，提高光捕获能力，减小带隙，上移最低的未占据分子轨道（LUMO）能级并增强生成的SMA的电荷传输。同时，对于IPYT-IC，氟化的IPYT-ICF具有更强的吸收能力，更窄的带隙，更高的电子迁移率和更低的最高占据分子轨道/ LUMO能级。使用聚合物PTB7-Th作为电子给体的基于IPYT-ICF的铸态PSC，以环保型邻二甲苯（XY）为加工溶剂，而无任何添加剂和后处理，可实现高达7.00％的功率转换效率由于基于更高的载流子迁移率，更好的电荷传输和收集特性，较弱的电荷重组以及优异的薄膜形态，这种处理比基于IPYT-IC的设备（4.50％）要高，主要来自更大的J _sc和FF。但是，基于IPYT-IC的设备表现出色V _oc高达0.98 V，因为弱电子缺乏的A'单元（IPY）使这些SMA的LUMO能级上移。我们的结果表明，弱电子不足的IPY可以成为有前途的A'单元，以开发用于无添加剂且环保的铸态PSC的高效A–DA'D–A型SMA。