Gopikrishna Peddaboodi, Choi Huijeong, Kim Do Hui, Hwang Jun Ho, Lee Youngwan, Jung Hyeonwoo, Yu Gyeonghwa, Raju Telugu Bhim, Lee Eunji, Lee Youngu, Cho Shinuk, Kim BongSoo
Department of Chemistry, Ulsan National Institute of Science and Technology (UNIST) 50 UNIST-gil Ulsan 44919 Republic of Korea
Department of Physics and EHSRC, University of Ulsan 93 Daehak-ro, Nam-gu Ulsan 44610 Republic of Korea
Chem Sci. 2021 Oct 13;12(42):14083-14097. doi: 10.1039/d1sc04153c. eCollection 2021 Nov 3.
The concurrent enhancement of short-circuit current ( ) and open-circuit voltage ( ) is a key problem in the preparation of efficient organic solar cells (OSCs). In this paper, we report efficient and stable OSCs based on an asymmetric non-fullerene acceptor (NFA) IPC-BEH-IC2F. The NFA consists of a weak electron-donor core dithienothiophen[3,2-]-pyrrolobenzothiadiazole (BEH) and two kinds of strong electron-acceptor (A) units [9-indeno[1,2-]pyrazine-2,3-dicarbonitrile (IPC) with a tricyclic fused system and 2-(5,6-difluoro-3-oxo-2,3-dihydro-1-inden-1-ylidene)malononitrile (IC2F)]. For comparison, the symmetric NFAs IPC-BEH-IPC and IC2F-BEH-IC2F were characterised. The kind of flanking A unit significantly affects the light absorption features and electronic structures of the NFAs. The asymmetric IPC-BEH-IC2F has the highest extinction coefficient among the three NFAs owing to its strong dipole moment and highly crystalline feature. Its highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels lie between those of the IPC-BEH-IPC and IC2F-BEH-IC2F molecules. The IPC group also promotes molecular packing through the tricyclic π-conjugated system and achieves increased crystallinity compared to that of the IC2F group. Inverted-type photovoltaic devices based on p-type polymer:NFA blends with PBDB-T and PM6 polymers as p-type polymers were fabricated. Among all these devices, the PBDB-T:IPC-BEH-IC2F blend device displayed the best photovoltaic properties because the IPC unit provides balanced electronic and morphological characteristics. More importantly, the PBDB-T:IPC-BEH-IC2F-based device exhibited the best long-term stability owing to the strongly interacting IPC moiety and the densely packed PBDB-T:IPC-BEH-IC2F film. These results demonstrate that asymmetric structural modifications of NFAs are an effective way for simultaneously improving the photovoltaic performance and stability of OSCs.
同时提高短路电流（ ）和开路电压（ ）是高效有机太阳能电池（OSC）制备中的关键问题。在本文中，我们报道了基于不对称非富勒烯受体（NFA）IPC-BEH-IC2F的高效且稳定的OSC。该NFA由一个弱电子供体核心二噻吩并噻吩[3,2-] - 吡咯并苯并噻二唑（BEH）和两种强电子受体（A）单元组成，即具有三环稠合体系的9-茚并[1,2-]吡嗪-2,3-二甲腈（IPC）和2-(5,6-二氟-3-氧代-2,3-二氢-1-茚-1-亚基)丙二腈（IC2F）。为作比较，对对称NFA IPC-BEH-IPC和IC2F-BEH-IC2F进行了表征。侧翼A单元的种类显著影响NFA的光吸收特性和电子结构。不对称的IPC-BEH-IC2F由于其强偶极矩和高结晶特性，在三种NFA中具有最高的消光系数。其最高占据分子轨道（HOMO）和最低未占据分子轨道（LUMO）能级介于IPC-BEH-IPC和IC2F-BEH-IC2F分子之间。IPC基团还通过三环π共轭体系促进分子堆积，与IC2F基团相比，实现了更高的结晶度。制备了基于p型聚合物：NFA共混物的倒置型光伏器件，其中以PBDB-T和PM6聚合物作为p型聚合物。在所有这些器件中，PBDB-T:IPC-BEH-IC2F共混器件表现出最佳的光伏性能，因为IPC单元提供了平衡的电子和形态特征。更重要的是，基于PBDB-T:IPC-BEH-IC2F的器件由于IPC部分的强相互作用和紧密堆积的PBDB-T:IPC-BEH-IC2F薄膜而表现出最佳的长期稳定性。这些结果表明，NFA的不对称结构修饰是同时提高OSC光伏性能和稳定性的有效方法。
