Interfacial Engineering of a PCBM/AZO Electron Transport Bilayer for Efficient and Stable Inverted Perovskite Solar Cells

Abstract The reduced hysteresis index and low‐temperature processed fabrication of inverted p‐i‐n perovskite solar cells (PSC) have attracted substantial attraction for achieving higher photovoltaic performance through interfacial engineering. Despite having certain limitations, fullerene‐based electron transport layers have been used frequently utilized in mixed halide inverted perovskite solar cells. The energy level mismatch between PCBM and metal electrode creates a hindrance in efficient electron extraction and thus a limiting factor in attaining higher device performances. In this work, we report an efficient interlayer of aluminum‐doped zinc oxide (AZO) nanoparticles in‐between PCBM and the metal electrode to suppress interfacial recombination. The PCBM/AZO electron transport bilayer can effectively mitigate the imperfections of the PCBM layer alone. The PCBM/AZO electron transport bilayer with an optimal concentration of 2% Al dopant exhibited greatly improved power conversion efficiency (PCE) of 18.63%, V_OC of 1.13 V, and FF of 73% with negligible hysteresis index of 0.04. Further, the optimal device exhibited remarkable stability by retaining 91% of the initial PCE after 200 hours confirming the suitable insertion of the AZO bilayer. The improved photovoltaic performance using PCBM/AZO bilayer can be attributed to higher electron transfer efficiency, suppressed interfacial recombination, and smooth surface morphology of AZO nanoparticles atop the PCBM layer.