Enhanced physical properties of pulsed laser deposited NiO films via annealing and lithium doping for improving perovskite solar cell efficiency

Pulsed laser deposition (PLD) is a powerful growth technique for thin films, where in situ doping and post-thermal annealing are the most effective ways to tune the crystalline and physical properties of the deposited films. This paper demonstrates that the crystallinity, transparency, and electrical properties of NiO films are well controlled by PLD, which determines the photovoltaic performance of CH3NH3PbI3-xClx-based perovskite solar cells with NiO films as the hole transport layers (HTLs). After post-annealing, the NiO films exhibit enhanced in-plane crystal orientation, high transmittance, and uniform surface morphology, and, accordingly, the power conversion efficiency (PCE) of the perovskite solar cell improves from 5.38% to 12.59%. Moreover, by doping the ablated target with lithium (Li), PLD can produce doped NiO: Li films with significantly enhanced electrical conductivity, which further improves the perovskite cell PCE from 12.59% to 15.51%. These results highlight the importance of optimizing the transporting layer properties toward high-performance inverted perovskite planar solar cells.