Achieving Desired Pseudo‐Planar Heterojunction Organic Solar Cells via Binary‐Dilution Strategy

Abstract The sequential deposition process has demonstrated the great possibility to achieve a photolayer architecture with an ideal gradient phase separation morphology, which has a vital influence on the physical processes that determine the performance of organic solar cells (OSCs). However, the controllable preparation of pseudo‐planar heterojunction (P‐PHJ) with gradient distribution has not been effectively elucidated. Herein, a binary‐dilution strategy is proposed, the PM6 solution with micro acceptor BO‐4Cl and the L8‐BO solution with micro donor PM6 respectively, to form P‐PHJ film. This architecture exists good donor (D) and acceptor (A) vertical gradient distribution and larger D/A interpenetrating regions, which promotes exciton generation and dissociation, shortens charge transport distance and optimizes carrier dynamics. Moreover, the dilution of PM6 by BO‐4Cl promotes the regulation of active layer aggregation size and phase purity, thus alleviating energy disorder and voltage loss. As a result, the P‐PHJ device exhibits an outstanding power conversion efficiency of 19.32% with an excellent short‐circuit current density of 26.92 mA cm −2 , much higher than planar binary heterojunction (17.67%) and ternary bulk heterojunction (18.49%) devices. This research proves a simple but effective method to provide an avenue for constructing desirable active layer morphology and high‐performance OSCs.