Boosting the Conductivity of the NiOx Layer through Cerium Doping for Efficient Planar Inverted Perovskite Solar Cells

The NiOx material as a representative p-type semiconductor is usually applied as the hole transport material (HTM) for planar inverted perovskite solar cells (PIPSCs) owing to its easy synthesis and low cost. However, the hole extraction efficiency at the interface between the NiOx and perovskite layers in PIPSCs is limited by the low conductivity of pure NiOx (2.67 x 10(-6) S cm(-1)). Herein, we demonstrate that 3 mol % cerium doping is able to boost the conductivity of the NiOx layer by about 4-fold and enhance the hole mobility by about 2 times. In addition, the defect density of the perovskite layer is reduced largely when the substrate is changed from NiOx to Ce:NiOx (3 mol %) since the Ce:NiOx (3 mol %) film is flatter than the pure NiOx film. The power conversion efficiency is thus enhanced from 15.05% for the control device with the undoped NiOx HTM to 17.87% for the PIPSC with the 3 mol % Ce-doped NiOx HTM. This work reveals that Ce:NiOx is a kind of promising HTM for efficient PIPSCs.