Quantum well-inspired energy level design in multicomponent organic solar cells for improved energy loss management.

The power conversion efficiency of organic solar cells (OSCs) has significantly improved since PM6:Y6 was introduced. However, the persistently inadequate energy loss management would constrain further advances towards >21% efficiency devices. Based on spin statistics, bimolecular recombination predominantly generates triplet-character intermediate states, which commonly undergo back charge transfer (BCT) followed by localized triplet formation and non-radiative decay, resulting in significant energy losses. Here, we introduced a strategy based on partial quantum confinement effects (PQCEs) through shallow quantum well-motif energy level configurations within the bulk of photoactive layers. This transiently localized the hole polarons to disrupt the thermodynamic balance, promoting the forward process towards dissociation, thereby impeding BCT and reducing energy loss. Notably, under optimal PQCE conditions, the donor-acceptor interface and overall molecular nanoscale network remain virtually unchanged. Accordingly, the PQCE will offer excellent synergies with existing morphology fine-tuning approaches, opening research avenues towards a new era of cost-effective OSCs.