Sequential Processing Leaves Trace A-D-A-type Acceptor as a Bifunctional Buried Interlayer for Efficient and Stable Inverted Organic Solar Cells.

Inverted organic solar cells (OSCs) offer advantages in stability and scalability, yet their efficiencies lag behind conventional devices due to metal oxide transport-layer defects and undesirable active-layer morphology. Here, we report a trace-residual buried interface (TRBI) strategy that simultaneously addresses both limitations. Specifically, a thin A-D-A-type acceptor (L8-BO) layer pre-deposited on ZnO leaves an anchored trace residue after active layer deposition. This ultrathin interlayer passivates surface defects of ZnO and upshifts the Fermi level while inducing ordered molecular packing of the acceptor at the buried interface. Consequently, electron transport and extraction are both accelerated, contributing to distinctly higher short-circuit current density and fill factor (FF). The strategy also proves universal across various primer acceptors and photoactive systems. With a ternary D18:PM6:CH1007 system, the resulting device achieves an efficiency of 18.7% with an FF of 80.59%, which are among the top values for inverted OSCs. It further delivers markedly enhanced thermal stability, with 91% PCE retention after 2000 h at 85°C, outperforming pristine ZnO and classic PFN-Br-modified references. Overall, this work demonstrates a buried-interface engineering strategy that concurrently suppresses multiple defects at the ZnO/active-layer contact, providing a simple yet effective route toward efficient and stable inverted OSCs.