Solid Additive‐Assisted Selective Optimization Strategy for Sequential Deposited Active Layers to Construct 19.16% Efficiency Binary Organic Solar Cells

Abstract Volatile solid (VS)‐additives are regarded as an effective tool to manipulate morphology of sequential deposited (SD) active layers for improving power conversion efficiencies (PCEs) of organic solar cells (OSCs), while the independent effect of VS‐additives on donor and acceptor layers is often overlooked. Herein, a new VS‐additive named 2‐(2‐methoxyphenyl)benzo[b]thiophene (BTO) is synthesized and applied in SD binary PM6/L8‐BO active layers. Introducing it into bottom PM6 layer (PM6+), BTO has a low volatility and longer volatilization distance, which prolongs the interaction time between BTO and L8‐BO in PM6+/L8‐BO film, leading to an over‐aggregated L8‐BO. While inserting it into top L8‐BO layer (L8‐BO+), the fast evaporation of BTO and excellent dipole interaction between BTO and L8‐BO help to enhance molecular absorption, crystallinity, and ordered packing of PM6/L8‐BO+ system. Therefore, an optimized morphology with proper phase separation is achieved to increase exciton dissociation and charge transfer properties, restrain charge recombination and energy loss of OSCs, yielding an impressive PCE of over 19%. Furtherly, using D18 instead of PM6, binary SD‐systems offer a record‐high PCE of 19.16%. The developed selective optimization strategy for SD active layers provides a deep insight into the working mechanism of VS‐additives for boosting PCE of OSCs.