Interface Engineering and Band Alignment Studies of Cu Doped NiO as a Hole Transport Layer for Triple Cationic Perovskite Solar Cells

Hole selective inorganic transport layer plays an important role for higher stability of p-i-n perovskite solar cell. Here, this study investigates optimized Cu doping in NiO hole transport layer (HTL) and studied its interface with triple cation perovskite (Cs_0.05(FA_0.83MA_0.17)_0.95Pb(I_0.83Br_0.17)₃) absorbing layer. The optimized Cu doped NiO shows optical band gap of 3.17 eV with high electrical mobility and moderate carrier concentration of 43.2 cm²/V-s and 1.51 × 10¹⁸ cm^-3, respectively. X-ray photoelectron spectroscopy analysis (XPS) shows modified Ni³⁺/Ni²⁺ ratio with Cu doping in NiO, which enhances hole mobility and conductivity of HTL. The band alignment, recombination losses, and charge transport in several devices (FTO/Cu:NiO/Cs_0.05(FA_0.83MA_0.17)_0.95Pb(I_0.83Br_0.17)₃/Au) are also investigated using capacitance- voltage (CV) and electrochemical impedance spectroscopy (EIS). Optimized HTL showed a lower trap density (5.20 × 10²⁰ cm^{- 2} eV^-¹), which resulted in a decrease of recombination losses and an increase in charge transport. The drift-diffusion model based simulation results also reveals the impact of interface defect density on power conversion efficiency (PCE). Final solar cell is fabricated on optimum Cu doped NiO HTL layers which showed an efficiency of 16.61% with enhanced fill factor (FF) of 77%. This study provides a detailed analysis of Cu doped NiO and their band alignment for a potential hole transport material in triple cation perovskite solar cells.