Molecular Orientation Unified Nonfullerene Acceptor Enabling 14% Efficiency As‐Cast Organic Solar Cells

• Published in: Advanced functional materials Vol. 29; no. 36
• Main Authors: Feng, Haohao, Song, Xin, Zhang, Zhuohan, Geng, Renyong, Yu, Jiangsheng, Yang, Linqiang, Baran, Derya, Tang, Weihua
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc 01.09.2019
• Subjects: as‐cast organic solar cells; Charge transport; dithieno[3,2‐b:2′,3′‐d]pyrrol; Energy conversion efficiency; Film thickness; Heterojunctions; Materials science; molecular orientation; nonfullerene acceptor; Organic chemistry; Orientation; Photovoltaic cells; Polymer blends; Solar cells; thickness insensitive
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.201903269

Molecular orientation and π–π stacking of nonfullerene acceptors (NFAs) determine its domain size and purity in bulk‐heterojunction blends with a polymer donor. Two novel NFAs featuring an indacenobis(dithieno[3,2‐b:2ʹ,3ʹ‐d]pyrrol) core with meta‐ or para‐alkoxyphenyl sidechains are designed and denoted as m‐INPOIC or p‐INPOIC, respectively. The impact of the alkoxyl group positioning on molecular orientation and photovoltaic performance of NFAs is revealed through a comparison study with the counterpart (INPIC‐4F) bearing para‐alkylphenyl sidechains. With inward constriction toward the conjugated backbone, m‐INPOIC presents predominant face‐on orientation to promote charge transport. The as‐cast organic solar cells (OSCs) by blending m‐INPOIC and PBDB‐T as active layers exhibit a power conversion efficiency (PCE) of 12.1%. By introducing PC71BM as the solid processing‐aid, the ternary OSCs are further optimized to deliver an impressive PCE of 14.0%, which is among the highest PCEs for as‐cast single‐junction OSCs reported in literature to date. More attractively, PBDB‐T:m‐INPOIC:PC71BM based OSCs exhibit over 11% PCEs even with an active layer thickness over 300 nm. And the devices can retain over 95% of PCE after storage for 20 days. The outstanding tolerance to film thickness and outstanding stability of the as‐cast devices make m‐INPOIC a promising candidate NFA for large‐scale solution‐processable OSCs. A meta‐alkoxylphenylated dithieno[3,2‐b:2′,3′‐d]pyrrol‐fused nonfullerene acceptor, featuring predominant face‐on orientation in films, enables high‐efficiency as‐cast thick organic solar cells (OSCs). Binary blends with PBDB‐T contributes to a 12.1% power conversion efficiency. Addition of 15 wt% PC71BM renders an efficiency of 14%, among the records for as‐cast single‐junction OSCs. All devices exhibit thickness insensitivity in an active layer thickness window of 82–202 nm.