Ion-beam sputtering of NiO hole transporting layers for p-i-n halide perovskite solar cells
Ion-beam sputtering offers significant benefits in terms of deposition uniformity and pinhole-free thin-films without limiting the scalability of the process. In this work, the reactive ion-beam sputtering of nickel oxide has been developed for the hole transporting layer of a p-i-n perovskite solar cells (PCSs). The process is carried out by oxidation of the scattered Ni particles with additional post-treatment annealing regimes. Using deposition rate of 1.2 nm/min allowed growth of very uniform NiO coating with the roughness below 0.5 nm on polished Si wafer (15x15 cm2). We performed a complex investigation of structural, optical, surface and electrical properties of the NiO thin-films. The post-treatment annealing (150-300C) was considered as an essential process for improvement of the optical transparency, decrease of defects concentration and gain of the charge carrier mobility. As result, the annealed ion-beam sputtered NiO films delivered a power conversion efficiency (PCE) up to 20.14%, while device without post-treatment reached the value of 11.84%. The improvement of the output performance originated from an increase of the short-circuit current density (Jsc), open circuit voltage (Voc), shunt and contact properties in the devices. We also demonstrate that the ion-beam sputtering of NiO can be successfully implemented for the fabrication of large area modules (54.5 cm2) and PSCs on a flexible plastic substrate (125 microns).