High-Efficiency Organic Photovoltaics with Two-Dimensional Conjugated Benzodithiophene-Based Regioregular Polymers

Abstract

We synthesized and characterized two kinds of regioregular polymers that were based on thieno[3,4-b]thiophene as an electron-accepting unit and benzo[1,2-b:4,5-b′]dithiophene as the electron-donating unit with different side chain, alkylthio and alkyl thiophenes, named rr-PTBS and rr-PTB7-Th, respectively. Because of the partial introduction of the alkylthio thiophene side chain, rr-PTBS showed red-shifted absorption and a deeper HOMO level compared to those of rr-PTB7-Th. In addition, both rr-PTBS:PC71BM and rr-PTB7-Th:PC71BM blended films showed face-on orientations stronger than those of regiorandom PTB7-Th. However, the rr-PTB7-Th:PC71BM blended film showed a peak in the out-of-plane direction much weaker than those of rr-PTBS:PC71BM and PTB7-Th:PC71BM blended films. Moreover, the rr-PTBS:PC71BM blended film exhibited charge carrier mobility (μe/μh ∼ 1.01) much more balanced than that of the rr-PTB7-Th:PC71BM blended film (μe/μh ∼ 1.23). The bulk-heterojunction organic photovoltaic (OPV) device based on rr-PTBS and the 1,8-diiodooctane additive showed a high power conversion efficiency (PCE) of 8.68%, while the OPV device based on rr-PTB7-Th and the 1,8-diiodooctane additive showed a PCE of 7.04%. Finally, an OPV device using rr-PTBS, the diphenyl ether additive, and Micro Lens Film exhibited a short-circuit current (Jsc) of 19.72 mA/cm2, an open-circuit voltage (Voc) of 0.82 V, and a fill factor (FF) of 63.82%, thus resulting in a PCE of 10.31%. © 2017 American Chemical Society.