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-x)CuxPbI3 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-x)CuxPbI3/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.