Cobalt benzoate interfacial engineering for efficient and stable perovskite solar cells

Interface-associated recombination at the interface of perovskite active layer/hole transport layer (PVK/HTL) remains an important loss pathway in high-performance perovskite solar cells (PSCs). In this work, cobalt benzoate [(C 6 H 5 COO) 2 Co, CoBz] is introduced as a post-treatment modifier to regulate the upper surface of the PVK before deposition of the HTL. The introduction of CoBz lowers the trap-state density from 4.16 × 10 15  cm −3 to 2.84 × 10 15  cm −3 , and enlarges the average grain size from 0.70 to 1.19 μm, improving the crystalline quality of perovskite. At the same time, the optimized interface facilitates charge extraction and transport and suppresses recombination losses. Benefiting from these effects, the CoBz-treated device delivers a power conversion efficiency of 23.84%, exceeding the value of 21.98% for the pristine device. Moreover, the unencapsulated modified device maintains 89.23% of its initial efficiency after 1000 h of exposure to air at 25 °C and 30% relative humidity, and 89.0% after 400 h of maximum power point tracking (MPPT) under N 2 . Overall, CoBz interfacial engineering offers an effective route to concurrently improve the efficiency and stability of PSCs.