Enhanced Carrier Recombination in Mixed-Phase CsPbI₃ through Controlled Cu Doping: Defect Suppression and Phase Modulation for Improved LEDs

Inorganic halide perovskites are excellent candidates as active materials for light-emitting diodes due to their outstanding and tunable luminescent characteristics, but their structural instability is still a pressing issue. However, doping transition metals is a promising and inexpensive strategy to improve the stability of perovskites. This study explores the impact of copper (Cu) doping on the structural and optoelectronic behavior of mixed-phase CsPbI₃, with an emphasis on electron-hole recombination and phase stability. Varying fractions of Cu were doped in the as-synthesized pristine CsPbI₃, comprising the cubic (α) and orthorhombic (γ) phases, and a marked enhancement in both the structural stability and optical properties of CsPbI₃ was observed. From temperature-dependent photoluminescence studies, we found that an optimal doping amount of 3.7% Cu increased the fraction of cubic phase in CsPbI₃ with minimization of intermediate transition states and reduced defect density. Light-emitting diodes based on the optimally doped CsPbI₃ demonstrate superior performance, including a reduced turn-on voltage of 2.5 V, increased current injection efficiency, 400% increase in electroluminescence intensity, and a 6-fold boost in operational stability compared to pristine CsPbI₃ devices. This work thus underscores the pivotal role of Cu doping in stabilizing specific phases and refining the optical properties of CsPbI₃, demonstrating their significant potential for optoelectronic device applications.