Molecular Bridge Assisted Bifacial Defect Healing Enables Low Energy Loss for Efficient and Stable Perovskite Solar Cells

Abstract Interface engineering is of paramount importance for optimizing carrier dynamics and stability of perovskite solar cells (PSCs), but little attention has been paid to understanding and managing the buried interfaces. Here, a molecular bridge strategy is developed to modify the properties of buried interfaces in n–i–p PSCs by introducing a multi‐functional additive 2‐Hydroxyethyl trimethylammonium chloride (ChCl) in the bottom SnO 2 electron transport layer. The ChCl treatment enables bifacial defects passivation and improved perovskite quality, leading to notably enhanced electron extraction and suppressed non‐radiative recombination at the buried interfaces. As a result, a significantly improved power conversion efficiency (PCE) from 20.0% to 23.07% with a remarkable open‐circuit voltage ( V oc ) of up to 1.193 V is achieved, along with superior stability (up to 4000 h) for the unsealed devices under different conditions (moisture, heat and maximum power point). Furthermore, this molecular bridge strategy demonstrates the ability to release the stress in perovskite thin film and simultaneously strengthen the interfacial toughness in flexible PSCs, yielding remarkable mechanical stability and a champion PCE of 21.50%. This study offers deep insights into understanding and engineering the buried interfaces and provides effective strategies to further enhance the performance and stability of PSCs.