Single-Layered MXene Nanosheets Doping TiO2 for Efficient and Stable Double Perovskite Solar Cells

The inorganic lead-free Cs₂AgBiBr₆ double perovskite structure is the promising development direction in perovskite solar cells (PSCs) to solve the problem of the instability of the APbX₃ structure and lead toxicity. However, the low short-circuit current and power conversion efficiency (PCE) caused by the low crystallization of Cs₂AgBiBr₆ greatly limit the optoelectronic application. Herein, we adopt a simple strategy to dope single-layered MXene nanosheets into titania (Ti₃C₂T_x@TiO₂) as a multifunctional electron transport layer for stable and efficient Cs₂AgBiBr₆ double PSCs. The single-layered MXene nanosheets significantly improve the electrical conductivity and electron extraction rate of TiO₂; meanwhile, the single-layered MXene nanosheets change the surface wettability of the electron transport layer and promote the crystallization of the Cs₂AgBiBr₆ double perovskite in solar cell devices. Therefore, the PCE went up by more than 40% to 2.81% compared to that of a TiO₂ based device, and the hysteresis was greatly suppressed. Furthermore, the device based on Ti₃C₂T_x@TiO₂ showed the long-term operating stability. After storing the device for 15 days under ambient air conditions, the PCE still remained a retention rate of 93% of the initial one. Our finding demonstrates the potential of Ti₃C₂T_x@TiO₂ in electron transfer material of high-performance double PSCs.