Ion-Beam Sputtering of NiO_x Hole Transporting Layers for p–i–n Halide Perovskite Solar Cells

Abstract

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 ionbeam 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).