Low-temperature processed planar perovskite solar cells based on bilayer electron transport layer stabilized using a surface defect passivation strategy

Tin oxide (SnO₂) and aluminum-doped zinc oxide (AZO) have been recognized as promising materials for the electron transport layer (ETL) in perovskite solar cells (PSCs) due to their favorable optoelectronic properties and low-temperature deposition processes. However, high surface trap density at the ETL/perovskite interface limits the further improvement of the power conversion efficiency (PCE) of planar PSCs. Herein, we have demonstrated a simple surface treatment of low-temperature deposited SnO₂/AZO–ETL through mono-ethanolamine (MEA) to passivate the defects at the AZO/perovskite interface and reduce carrier recombination. Meanwhile, after MEA modification, the defect states at the AZO/perovskite interface were reduced, and the carrier transport capability was improved. PSC based on MEA modification showed an enhanced PCE of 15.73%, compared to 12.66% without MEA treatment, and a fill factor (FF) of 68.30% on a 0.25 cm² active area. Furthermore, the MEA-passivated device exhibits excellent stability and retains ~ 77% of its initial PCE after 1000 h under ambient storage without encapsulation. Thus, interface engineering based on the mono-ethanolamine passivation provides a feasible and novel strategy to improve the quality of ETL to fabricate high-efficiency planar PSCs.