Efficient polymer solar cells based on a new benzo[1,2-b:4,5-b′]dithiophene derivative with fluorinated alkoxyphenyl side chain

Abstract

A novel fluorine-containing benzo[1,2-b:4,5-b′]dithiophene (BDT) derivative (BDTPF) was designed to construct a donor–acceptor (D–A)-structured polymer (PBDTPF-DTBT) with the electron-withdrawing unit 4,7-di(4-(2-ethylhexyl)-2-thienyl)-2,1,3-benzothiadiazole (DTBT). The resulting polymer exhibits a broad absorption spectrum, relatively low lying HOMO energy level (−5.39 eV) and a good film-forming ability. The field-effect mobility of PBDTPF-DTBT is 0.034 cm² V⁻¹ s⁻¹. Bulk heterojunction organic solar cells (OSCs) based on PBDTPF-DTBT and PC₇₁BM were prepared and showed a good photovoltaic performance with power conversion efficiency (PCE) of 7.02%. This work demonstrates that a BDT unit with fluorinated alkoxyphenyl side chains is a promising candidate as an electron-rich building block for high performance solution-processed OSCs.