Boosting Binary Organic Solar Cells Over 20% Efficiency via Synchronous Modulation of Charge Transport and Phase Morphology

Abstract Reducing insufficient charge transport of bulk heterojunction (BHJ) photoactive layer is a key challenge for realizing efficient organic solar cells (OSCs). To address this issue, a synergistic modulation strategy is developed via introducing a highly crystalline p‐type organic semiconductor C8‐BTBT as a solid additive into a binary system consisting of a polymer donor PM6 and a nonfullerene acceptor L8‐BO, to simultaneously improve charge dynamics and phase morphologies. Resulting binary OSCs yield a remarkable efficiency of 20.1% with an impressive fill factor (FF) of 81.9%. The achieved FF is the highest reported so far for the PM6:L8‐BO community. The competitive advantages of the modified photoactive layer are attributed to matched electronic structures that facilitate exciton dissociation at donor: acceptor heterointerface, reduced charge trap densities, more balanced charge mobilities, and suppressed charge recombinations, evidently demonstrated by a series of transient characterization technologies and quantitative theoretical analyses. Moreover, the optimized micromorphology features uniform fibrillar structures with improved dispersity, significantly promoting electrical properties. This work sheds light on a promising strategy for addressing the BHJ charge transport challenge and further enhancing the performance of OSCs.