Solid solution effect boosts the photovoltaic performance of PCDTBT-based organic solar cells

Abstract

Cheap conjugated polymer PCDTBT and its derivatives are rarely used in high-efficiency non-fullerene acceptor (NFA) organic solar cells (OSCs) due to their poor charge transport property. Herein, solid solution strategy is employed to boost the photovoltaic performance of PCDTBT:NFA-based OSCs. The PCDTBT-OR:PC 71 BM solid solution is formed when a small amount of PC 71 BM molecules are dispersed within amorphous PCDTBT-OR matrix due to their thermodynamic miscibility, which demonstrates increased hole mobility with comparison to the neat PCDTBT-OR. The hole mobility of ternary PCDTBT-OR:PC 71 BM:Y6 blend containing a small amount of PC 71 BM is also increased significantly due to the PCDTBT-OR:PC 71 BM solid solution effect. The ternary PCDTBT-OR:PC 71 BM:Y6 blend shows better charge extraction, less bimolecular recombination as well as more efficient charge transfer. Finally, the PCDTBT-OR:PC 71 BM:Y6 OSCs achieve a power conversion efficiency (PCE) of 8.42%, much higher than 6.82% of the binary PCDTBT-OR:Y6 OSCs, and it is also one of the highest values for PCDTBT:NFA-based OSCs. This work demonstrates that the cheap polymer donor PCDTBT derivatives have potential to achieve high PCE in combination with NFAs. Solid solution effect of PCDTBT-OR:PC 71 BM blend is favorable to enhance hole mobility of donor phase and renders the PCDTBT-OR:Y6-based organic solar cells (OSCs) an optimized PCE of 8.42%, which is one of the highest values for the PCDTBT:NFAs based OSCs. • Solid solution effect is utilized to improve the photovoltaic performance of PCDTBT-OR:NFA OSCs. • PC 71 BM molecules tend to disperse in PCDTBT-OR matrix to form solid solutions. • Solid solution effect is favorable to improve hole transport in PCDTBT-OR:PC 71 BM blend film. • Solid solution effect enhances the hole mobility and suppresses bimolecular recombination in the ternary blend. • The optimized device achieves a PCE of 8.42%, which is one of the highest values for the PCDTBT:NFA based OSCs.