Improving Uniformity and Reproducibility of Hybrid Perovskite Solar Cells via a Low-Temperature Vacuum Deposition Process for NiOx Hole Transport Layers.

Recently, the trend in inverted hybrid perovskite solar cells (PVSCs) has been to utilize NiOx as hole transport layers. However, the majority of reported solution-processed NiOx 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 NiOx 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 NiOx, which are responsible for a lower transmittance but higher conductivity. Most importantly, e-beam-evaporated NiOx-based PVSCs show greater uniformity and reproducibility compared to spin-coated NiOx-based PVSCs. Finally, e-beam-evaporated NiOx 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 NiOx.