Binary non-fullerene-based polymer solar cells with a 430 nm thick active layer showing 15.39% efficiency and 73.38% fill factor

Thickness-sensitive fill factor (FF) is usually encountered by organic active layers with a thickness of several hundred nanometers, which significantly deteriorate the photovoltaic performance of thick-film polymer solar cells (PSCs). Here, paring of high-hole mobility (mu(h)) polymer donor Si25 with benzotriazole-fused Y-series non-fullerene acceptor Y14 is proposed to overcome this challenge. Relative to the electron mobility (mu(e)) of 8.17 x 10(-4) cm(2) V-1 s(-1) for the Y14 pristine film, much higher mu(e) values up to 3.79 x 10(-3) cm(2) V-1 s(-1) were demonstrated using Si25:Y14 binary blend films, achieving mu(h)/mu(e) of 2.31-3.56. The Si25-induced closer packing of Y14 molecules was observed with the blend film. The high and fairly balanced charge transport-enabled PSCs with 320-600 nm thick active layers to show a low FF decay from 74.69% to 67.46%. Power conversion efficiencies (PCEs) of 15.39% and 15.03% were achieved for 430 nm and 600 nm thick active layers, respectively. The device performances can supply a wide processing window with high efficiency. Delightedly, green solvent o-xylene cast active layers of 400 nm and 530 nm thickness exhibited PCEs of 14.43% and 14.25%, respectively. This study indicates that high mu(h) polymers and benzotriazole-fused Y-series non-fullerene acceptors are promising candidates to overcome the thickness sensitivity of FF.

Automated summary

This study proposes a solution to the thickness-sensitive fill factor (FF) issue in thick-film polymer solar cells by pairing high-hole mobility polymer donor Si25 with benzotriazole-fused Y-series non-fullerene acceptor Y14. The combined films showed higher electron mobility values and balanced charge transport, leading to improved PSCs performance with reduced FF decay. The results suggest that high mu(h) polymers and benzotriazole-fused Y-series non-fullerene acceptors are promising candidates to overcome the thickness sensitivity of FF.