Ion-Beam Sputtering of NiO_x 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 p–i–n perovskite solar cells (PSCs). The process is carried out by the oxidation of the scattered Ni particles with additional post-treatment annealing regimes. Using a deposition rate of 1.2 nm/min allowed the growth of a very uniform NiO x coating with the roughness below 0.5 nm on polished Si wafer (15 × 15 cm 2 ). We performed a complex investigation of structural, optical, surface, and electrical properties of the NiO x thin films. The post-treatment annealing (150–300 °C) was considered an essential process for the improvement of optical transparency, decrease of defect concentration, and gain of charge carrier mobility. As a result, the annealed ion-beam-sputtered NiO x films delivered a power conversion efficiency (PCE) up to 20.14%, while the 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 ( J sc ), open-circuit voltage ( V oc ), shunt, and contact properties in the devices. We also demonstrate that the ion-beam sputtering of NiO x can be successfully implemented for the fabrication of large area modules (54.5 cm 2 ) and PSCs on a flexible plastic substrate (125 μm).