Efficient modulation of end groups for the asymmetric small molecule acceptors enabling organic solar cells with over 15% efficiency

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Materials for energy and sustainability, 2020-03, Vol.8 (12), p.5927-5935
• Main Authors: Li, Gang, Li, Dandan, Ma, Ruijie, Liu, Tao, Luo, Zhenghui, Cui, Guanwei, Tong, Lili, Zhang, Ming, Wang, Zaiyu, Liu, Feng, Xu, Liang, Yan, He, Tang, Bo
• Format: Article
• Language: English
• Subjects: Asymmetry; Charge transport; Chlorine; Circuits; Design optimization; Electronegativity; Energy conversion efficiency; Energy levels; Excitons; Fullerenes; Open circuit voltage; Phase separation; Photovoltaic cells; Short circuit currents; Short-circuit current; Solar cells; Tradeoffs
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/d0ta01032d

Non-fullerene organic solar cells (OSCs) have attracted tremendous interest and made an impressive breakthrough, largely due to advances in high-performance small molecule acceptors (SMAs). The relationship between short-circuit current density ( J SC ) and open-circuit voltage ( V OC ) is usually shown as one falls, the other rises. Controlling the trade-off between J SC and V OC to harvest high power conversion efficiencies (PCEs) still remains as a challenge. Herein, dithieno[3,2- b :2′,3′- d ]pyrrole (DTP) based asymmetric SMAs with different chlorinated dicyanoindanone-based end groups, named TPIC, TPIC-2Cl and TPIC-4Cl, are designed and synthesized. These asymmetric acceptors exhibit a remarkable red-shifted absorption profile, while energy levels are simultaneously down-shifted when the numbers of chlorine atoms alter from 0, 1 to 2, due to the gradually improved electronegativity. As a result, PM7:TPIC-4Cl based OSCs achieved a champion PCE of 15.31%, which is the highest PCE for non-fullerene binary OSCs based on asymmetric SMAs. The superiority of the PM7:TPIC-4Cl system consists of the balanced charge transport, favorable phase separation, efficient exciton dissociation and extraction, coupled with the remarkable π-π stacking and crystallinity of the SMAs. Our results highlight the important strategy of asymmetric molecular design to optimize the trade-off between V OC and J SC , reaching a high PCE. Three asymmetric SMAs based on dithieno[3,2- b :2′,3′- d ]pyrrole that exhibit a high efficiency of 15.31%, which is the highest value in asymmetric acceptor-based binary organic solar cells.