Interfacial energy level tuning for efficient and thermostable CsPbI₂Br perovskite solar cells

Inorganic mixed-halide CsPbX₃-based perovskite solar cells (PeSCs) are emerging as one of the most promising types of PeSCs on account of their thermostability compared to organic–inorganic hybrid counterparts. However, dissatisfactory device performance and high processing temperature impede their development for viable applications. Herein, a facile route is presented for tuning the energy levels and electrical properties of sol–gel-derived ZnO electron transport material (ETM) via the doping of a classical alkali metal carbonate Cs2CO3. Compared to bare ZnO, Cs₂CO₃-doped ZnO possesses more favorable interface energetics in contact with the CsPbI2Br perovskite layer, which can reduce the ohmic loss to a negligible level. The optimized PeSCs achieve an improved open-circuit voltage of 1.28 V, together with an increase in fill factor and short-circuit current. The optimized power conversion efficiencies of 16.42% and 14.82% are realized on rigid glass substrate and flexible plastic substrate, respectively. A high thermostability can be simultaneously obtained via defect passivation at the Cs₂CO₃-doped ZnO/CsPbI₂Br interface, and 81% of the initial efficiency is retained after aging for 200 h at 85 °C.