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

摘要

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 V-OC of 0.86 V, a J(SC) of 13.32 mA cm(-2) and a FF of 66.8% due to its high hole mobility (1.1 X 10(-3) cm(2) 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. (C) 2016 Elsevier Ltd. All rights reserved.