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

The effect of NiOx (0 < x) hole transport layer prepared by a radio-frequency sputtering method on the photovoltaic properties of planer-type CH3NH3PbI3 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 NiOx prepared at various powers. Assuming that the recombination effect can be neglected, the open circuit voltage (VOC) decrease with increasing power is due to the shifted WF to higher energy levels. (C) 2018 The Japan Society of Applied Physics