Simultaneously Optimizing Molecular Stacking and Phase Separation via Solvent‐Solid Hybrid Additives Enables Organic Solar Cells with over 19% Efficiency^†

Abstract

Comprehensive SummaryGiven the crucial role of film morphology in determining the photovoltaic parameters of organic solar cells (OSCs), solvent or solid additives have been widely used to realize fine‐tuned film morphological features to further improve the performance of OSCs. However, most high‐performance OSCs are processed only using single component additive, either solvent additive or solid additive. Herein, a simple molecular building block, namely thieno[3,4‐b]thiophene (TT), was utilized as the solid additive to coordinate with the widely used solvent additive, 1‐chloronaphthalene (CN), to modulate the film morphology. Systematical investigations revealed that the addition of TT could prevent the excessive aggregation to form a delicate nanoscale phase separation, leading to enhanced charge transport and suppressed charge recombination, as well as superior photovoltaic performance. Consequently, the PM6:Y6 based OSCs with the addition of hybrid additive of CN + TT demonstrated the optimal PCE of 18.52%, with a notable FF of 79.6%. More impressively, the PM6:Y6:PC71BM based ternary OSCs treated with the hybrid additives delivered a remarkable efficiency of 19.05%, which ranks among the best values of Y6‐based OSCs reported so far. This work highlights the importance of the hybrid additive strategy in regulating the active layer morphology towards significantly improved performance.