1 V high open-circuit voltage fluorinated alkoxybiphenyl side-chained benzodithiophene based photovoltaic polymers

Abstract

Utilizing two-dimensional (2-D) conjugated structure and extending two-dimensional π-conjugation system with benzene can improve the performance of the BDT-based polymer solar cells (PSCs). In this work, combining with strong electron-drawing ability of fluorine atom, a new monomer BBFBDT with fluorinated alkoxybiphenyl unit as side-chain was designed and synthesized to construct medium band-gap donor (D) - acceptor (A) copolymer P1 with a benzo[1,2- c:4,5-c’]dithiophene-4,8-dione (BDD) acceptor. Blending with a classical non-fullerene acceptor ITIC, the P1-based PSCs reached a power conversion efficiency (PCE) of 4.16% and when coupled with a fullerene acceptor PC71BM, the PCE of PSCs reached 4.66% with an open-circuit voltage (Voc) of 0.93 V, a short-circuit current density (Jsc) of 9.83 mA cm−2 and a fill factor (FF) of 50.97%. The relatively poor Jsc of P1-based devices may be caused by the bad complementarity of absorption spectra. Furthermore, a wide band-gap D-A copolymer P2, with a electron-deficient 4,7-bis(5-bromothiophen-2-yl)-2-((2-ethylhexyl)oxy)-5,6-difluoro-2H-benzo[d][1,2,3]triazole (TZ) as the acceptor unit, was synthesized to match the absorption spectra of ITIC. Finally, the efficiency achieved 6.59% with Voc of 0.99 V, Jsc of 14.37 mA cm−2 and FF of 46.32%.