Improving Uniformity and Reproducibility of Hybrid Perovskite Solar Cells via a Low-Temperature Vacuum Deposition Process for NiO<i>_x</i> Hole Transport Layers

Abstract

Recently, the trend in inverted hybrid perovskite solar cells (PVSCs) has been to utilize NiO_x as hole transport layers. However, the majority of reported solution-processed NiO_x films require a high-temperature thermal annealing process, which is unfavorable for large-scale manufacturing and suffers from lack of uniformity. We report, for the first time, e-beam evaporation as a low-temperature vacuum process for the deposition of NiO_x hole transport layers for PVSCs. Device characterization shows that efficiency is on par with solution-processed methods, the highest efficiency at 15.4% with no obvious hysteresis. Differences are found to be due to the presence of more Ni³⁺ in e-beam evaporated NiO_x, which are responsible for a lower transmittance but higher conductivity. Most importantly, e-beam-evaporated NiO_x-based PVSCs show greater uniformity and reproducibility compared to spin-coated NiO_x-based PVSCs. Finally, e-beam-evaporated NiO_x has the additional advantage of being produced by a low-temperature deposition process and applicable over large areas. This work, therefore, represents a significant step toward large-area PVSCs, where e-beam evaporation can be used for the low-temperature uniform deposition of charge-transport layers, such as NiO_x.