16.52% Efficiency All‐Inorganic Perovskite Solar Cells via Al‐Doped ZnO/SnO ₂ Electron Transport Bilayer for Improved Interfacial Energy‐Level Alignment

ABSTRACT

Interfacial energy‐level misalignment in all‐inorganic perovskite solar cells generally causes inefficient charge extraction. Here, we propose an Al‐doped ZnO (AZO)/SnO ₂ electron transport bilayer to improve energy‐level alignment in CsPbI ₂ Br‐based PSCs. By this approach, we achieved a champion efficiency of 16.52%, which is the highest reported value for all‐inorganic CsPbI ₂ Br PSCs without doping or passivation of the perovskite, along with a high V _OC of 1.33 V. AZO‐based devices substantially outperform ZnO‐based controls, delivering a PCE of 16.52% versus 15.21%, with suppressed dark current, reduced trap density, lower non‐radiative recombination, and smaller hysteresis. The AZO device retains 80% of its initial efficiency after 662 h of continuous illumination, compared with only 312 h for the ZnO counterpart. Al ³⁺ substitution for Zn ²⁺ elevates the ZnO conduction band minimum, establishing a favorable cascade alignment among SnO ₂ /AZO/perovskite that lowers the electron extraction barrier and blocks hole backflow. Al doping also suppresses oxygen vacancies, reducing interfacial trap‐state density and enhancing perovskite crystallinity. Efficient charge extraction further suppresses Ag electrode degradation and corrosion, contributing to long‐term stability. This work establishes a rational interfacial engineering approach using an AZO/SnO ₂ bilayer for efficient and stable all‐inorganic perovskite solar cells.