A new narrow bandgap polymer as donor material for high performance non-fullerene polymer solar cells

Abstract

Abstract Polymer solar cells (PSCs) based on narrow bandgap (NBG) photovoltaic materials have attracted significant attention due to their unique applications in semitransparent devices and organic tandem solar cells. In this work, we design and synthesize a new NBG polymer PBTT based on 2-(2-ethylhexyl)-thienyl substituted benzodithiophene (BDT-T) and n-octyl-3-fluorothieno[3,4-b]thiophene-2-carboxylate (TT) as donor material for the applications in non-fullerene PSCs. Compared with the widely used NBG polymer PTB7-Th, PBTT exhibited higher film extinction coefficient of 9.27\u202f×\u202f10 4\u202fcm−1, higher-lying energy levels, more ordered molecule packing and higher hole mobility of 2.13\u202f×\u202f10 −3\u202fcm2\u202fV−1 s −1. The PSCs based on PBTT: IEICO obtained a power conversion efficiency (PCE) of 9.5% with a Voc of 0.86\u202fV, a Jsc of 17.9\u202fmA\u202fcm−2 and a FF of 61.3%, which is significantly enhanced over that (7.3%) of the corresponding devices with PTB7-Th as donor. The significantly improved PCE could be attributed to the higher charge mobility and the improved morphology of the PBTT: IEICO blend film. These results demonstrate that PBTT is a very promising NBG polymer donor material for the applications in non-fullerene PSCs.