Effect of hydroxyl groups in NiO x on the open circuit voltage of lead iodide perovskite solar cells

Abstract The effect of NiO x (0 < x ) hole transport layer prepared by a radio-frequency sputtering method on the photovoltaic properties of planer-type CH 3 NH 3 PbI 3 perovskite solar cells (PVSCs) was investigated. The open circuit voltage of PVSC decreases with increasing applied power of the sputtering machine. The lack of hydroxyl groups on the surface of the metal oxides shifts the work function ( WF ) to higher energy levels. The X-ray photoelectron peaks of Ni 2p 3/2 at 855.6 eV and O 1s at 531.3 eV assigned to ONi(OH) decrease with the increasing power. Therefore, the decrease in the number of hydroxyl groups must have shifted the WF to higher energy levels. The shunt resistance of current–voltage curve and the internal quantum efficiency of the PVSCs is independent of NiO x prepared at various powers. Assuming that the recombination effect can be neglected, the open circuit voltage ( V OC ) decrease with increasing power is due to the shifted WF to higher energy levels.