Nonhalogen Solvent‐Processed Asymmetric Wide‐Bandgap Polymers for Nonfullerene Organic Solar Cells with Over 10% Efficiency

• Published in: Advanced functional materials 2018-04, Vol.28 (16), p.n/a
• Main Authors: An, Yongkang, Liao, Xunfan, Chen, Lie, Yin, Jingping, Ai, Qingyun, Xie, Qian, Huang, Bin, Liu, Feng, Jen, Alex K.‐Y., Chen, Yiwang
• Format: Article
• Language: English
• Subjects: Asymmetric structures; asymmetric units; Asymmetry; Charge transport; Donor materials; Efficiency; Electron transport; Energy conversion efficiency; Energy levels; Fullerenes; Materials science; Mathematical morphology; nonfullerenes; nonhalogen process; organic solar cells; Photovoltaic cells; Polymers; Solar cells; Solvents; Steric hindrance
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.201706517

Two new wide‐bandgap D–A–π copolymer donor materials, PBDT‐2TC and PBDT‐S‐2TC, based on benzodithiophene and asymmetric bithiophene with one carboxylate (2TC) substituent are synthesized by a facile approach for fullerene‐free organic solar cells (OSCs). The combination of one carboxylate‐substituted thiophene with one thiophene bridge in the backbone substantially reduces the steric hindrance, thereby favoring a planar geometry for efficient charge transport and molecular packing. A reasonable highest‐occupied‐molecular‐orbital energy level in relation to that of the acceptor and balanced hole and electron transport are observed for both polymers. This asymmetric structure unit is flexible and versatile, allowing the absorption, energy levels, and morphology of the blend films to be tailored. Fullerene‐free OSCs based on PBDT‐S‐2TC:ITIC achieve a high power conversion efficiency of 10.12%. More impressively, a successful nonhalogen solvent‐processed solar cell with 9.55% efficiency is also achieved, which is one of the highest values for a fullerene‐free OSC processed using an ecofriendly solvent. New wide‐bandgap D–A–π copolymers based on an asymmetric bithiophene with one carboxylate substituent were synthesized. The asymmetric structure unit is flexible and versatile, which allows the absorption, energy levels and morphology of the blend films to be adjusted easily. D‐A‐p copolymers produced a high power conversion efficiency of 10.0% for halogen solvent‐processed OSCs and 9.55% for non‐halogen solvent‐processed devices.