Dual Additive‐Assisted Layer‐by‐Layer Processing for 19.59% Efficiency Quasi‐Bulk Heterojunction Organic Solar Cells

Abstract The ideal vertical phase separation active layer morphology is crucial for the photoelectric conversion of organic solar cells. In this work, a layer‐by‐layer sequential deposition method is used to prepare D18/L8‐BO‐based organic solar cells and a dual additives strategy is adopted to construct the ideal active layer. Additive DIM regulates the crystallization of the D18 layer, and additive DIO induces L8‐BO to diffuse into the interior of the D18 layer to form a vertical composition distribution with large donor/acceptor interpenetrated regions. The improvement of active layer induced by DIM and DIO dual additives promote exciton generation and dissociation, shorten charge transfer distance, and improve carrier dynamics. With improved charge transport performance and suppressed carrier recombination, the short‐circuit current density and fill factor of the D18/L8‐BO quasi‐bulk heterojunction organic solar cells are improved simultaneously, and the power conversion efficiency is boosted significantly from 18.21% to 19.59%. Moreover, the improved photovoltaic performance is further verified in D18/Y6 and PM6/L8‐BO‐based organic solar cells, which implies the generalizability of the dual additive‐assisted layer‐by‐layer ‐sequential deposition method.