Suppressing Nonradiative Losses via Computation‐Guided Molecular Design of Self‐Assembled Interfacial Layers for High‐Performance Organic Solar Cells

The rational design of efficient self-assembled interlayers (SAIs) is pivotal for overcoming the efficiency bottleneck in organic solar cells (OSCs), in which substantial nonradiative energy losses limit further performance improvements. In this study, guided by theoretical calculations, we report a series of new SAI materials (BT-nBZCz; n = 2, 3, and 4) based on a benzocarbazole core functionalized with a benzo[b]thiophene (BT) unit, and systematically investigate their impact on nonradiative losses and OSC performance. Notably, binary OSCs incorporating BT-4BZCz achieve a significantly higher power conversion efficiency (PCE) of 20.46% compared to 18.08% for BT-free SAIs. Combined theoretical and experimental analyses reveal that BT functionalization improves energy level alignment, enhances dipole moment, and optimizes molecular packing, crystallization kinetics, and fibrillar network formation relative to BT-free SAIs. These improvements promote more efficient exciton dissociation, reduce charge recombination, and in particular, suppress nonradiative energy losses (0.284 vs. 0.217 eV) in the corresponding OSCs. Furthermore, BT-4BZCz exhibits excellent universality, maintaining high performance across various binary photoactive blends. This work presents a viable molecular engineering strategy for SAIs to suppress nonradiative losses and advance the development of high-performance OSCs.