Efficient thick film all-polymer solar cells enabled by incorporating an ester-substituted non-fullerene-based polymer acceptor†

Abstract

The low tolerance of thickness variations in all-polymer solar cells (all-PSCs) is currently becoming a new challenge to achieving efficient power conversion efficiencies (PCEs) and large-scale production. Compared with small molecular acceptors (SMA) systems, polymer acceptors in all-PSCs usually possess lower crystalline properties and imbalanced charge transportation characteristics, which limit their active layer thicknesses and PCEs. In this work, ester-substituted side chains were incorporated onto a thiophene–vinylene–thiophene (TVT) backbone to construct a non-fullerene Y-series polymer acceptor. It exhibited strengthened π–π stacking and higher charge mobility than its alkyl-substituted counterpart. When the ester-substituted polymer acceptor was blended with the donor PM6, it delivered a champion PCE of 16.48% with a high V_oc and FF. Impressively, the device efficiencies are insensitive to variation in the photoactive layer thickness and can maintain over 80% of the optimized efficiency as the film thickness increases to 400 nm, which is the best result for an all-PSC so far. This work not only achieved synergism between high efficiency and thickness-insensitivity in an all-PSC device, but also demonstrated that the TVT-containing backbone can be further optimized by incorporating reasonable functional groups to construct highly crystalline Y series polymer acceptors.