Comparison of NiOx thin film deposited by spin-coating or thermal evaporation for application as a hole transport layer of perovskite solar cells

Abstract

We compared nickel oxide (NiO_x) deposited by thermal evaporation and that deposited by the spin-coating process, for use in the hole transport layers of inverted planar perovskite solar cells (PSCs). Spin-coating deposition for NiO_x HTL has been widely used, owing to its simplicity, low cost, and high efficiency. However, the spin-coating process has a technical limit to depositing a large-area uniformly. In contrast, thermal evaporation fabrication has a low price and is able to produce uniform and reproducible thin film. Hence, the chemical states, energy band alignment, surface morphologies, and microstructures of NiO_x deposited by spin coating and thermal evaporation were analyzed. The PSC with NiO_x HTL deposited by thermal evaporation showed a higher power conversion efficiency of 16.64% with open circuit voltage 1.07 V, short circuit current density of 20.68 mA cm⁻², and a fill factor of 75.51% compared to that of PSC with spin-coated NiO_x. We confirmed that thermal evaporation can deposit NiO_x to give a better performance as a HTL with higher reproducibility than spin-coating.