Bisalkylthio side chain manipulation on two-dimensional benzo[1,2-b:4,5-b′]dithiophene copolymers with deep HOMO levels for efficient organic photovoltaics

• Published in: Dyes and pigments 2017-01, Vol.136, p.312-320
• Main Authors: Yu, Jiangsheng, Yin, Xinxing, Xu, Zhongsheng, Deng, Ping, Han, Yingbin, Zhou, Baojing, Tang, Weihua
• Format: Article
• Language: English
• Subjects: Benzo[1,2-b:4,5-b′]dithiophene; Bisalkylthio side chain; Deep HOMO levels; Organic photovoltaics
• ISSN: 0143-7208; 1873-3743
• DOI: 10.1016/j.dyepig.2016.08.057

In this study, three copolymers containing bisalkylthio side chain modifying two-dimensional benzo[1,2-b:4,5-b′]dithiophene (BDT) donor with different electron-deficient acceptors were synthesized. The copolymers were characterized using a combination of thermal analysis, UV–visible spectroscopy, cyclic voltammetry, and theoretical calculations. All copolymers exhibit deep HOMO energy levels from −5.52 eV to −5.60 eV, correspondingly resulting in high VOC. The photovoltaic properties of the copolymers were also studied systematically. The best devices blending PBDT-DTBTff with PC71BM exhibited a best PCE of 7.65%, with a VOC of 0.86 V, a JSC of 13.32 mA cm−2 and a FF of 66.8% due to its high hole mobility (1.1 × 10−3 cm2 V−1 s−1) and facilitated exciton dissociation and charge transport. This work demonstrates an effective method to tune HOMO energy levels of BDT-based copolymers through introducing bisalkylthio side chain into BDT donor. And this result also demonstrates the significance of the interaction and match between donor-acceptor units providing related polymer with suitable band gap and HOMO/LUMO energy levels. [Display omitted] •We demonstrated the synthesis of dialkylthiobenzo[1,2-b:4,5-b′]dithiophene based polymers.•We demonstrated the electrochemical characterization and molecular simulation of polymers.•We demonstrated the enhanced cell performance using solvent additive.•We demonstrated the highest PCE of 7.65% for PBDT-DTBTff based OPVs.