Fermi level alignment by copper doping for efficient ITO/perovskite junction solar cells

Different from band edge alignment, the Fermi level mismatch induced by band bending can manipulate charge collection at the ITO/(CH₃NH₃)_1-xCu_xPbI₃ heterojunctions. In this work, we employed a feasible spin-coating process to prepare copper defect compensation in CH₃NH₃PbI₃. The related work function was shown to shift with the copper doping density by Kelvin probe force microscopy (KPFM). Next, we applied transient surface photovoltage (TSPV) spectroscopy and first-order series reactions simulations to confirm that interface charge recombination at the ITO/perovskite junction can be eliminated through Cu⁺ doping. Nanoelectric photoconductive AFM analysis showed enhanced charge transfer and a higher photovoltage at the ITO/Cu-perovskite junction. Owing to efficient Fermi level alignment, the ITO/(CH₃NH₃)_1-xCu_xPbI₃/PCBM/Ag devices displayed high power conversion efficiencies of 15.14 ± 0.67% at ambient conditions for inverted perovskite solar cells without any hole transport layer.