Influence of Fluorine Doping on Hole Transport Properties of NiOx for High-Efficiency Perovskite Solar Cells

In perovskite solar cells (PSCs), the hole transport layer (HTL) is a crucial component, especially in inverted PSCs, which require enhanced cost efficiency, high mobility, excellent transmittance, and stability. The performance of inverted perovskite solar cells remains lower than the regular PSCs because of interfacial defects, poor electrical conductivity, and unfavorable band alignment between the perovskite and the HTL (NiOx). In this work, fluorine-incorporated nickel oxide (F doped NiOx) NPs are prepared using a co-precipitation approach and subsequently used as a HTL in the PSCs. Fluorine is effectively incorporated into the NiOx, resulting in strong bonding and a more stable structure, which passivates the hydroxyl groups from the NiOx surface and decreases defect sites. Moreover, fluorine is established as an efficient dopant for nickel oxide, which minimizes the formation of nickel vacancies while simultaneously enhancing the density of Ni³⁺ ions. Additionally, the electronic conductivity was enhanced, and the work function was increased with the F-doped NiOx film, which can facilitate hole extraction and reduce the recombination rate. Therefore, the F-doped NiOx PSCs achieved a remarkable power conversion efficiency of up to 20.78%. The F-doped NiOx also lead to improvement in stability under several environmental conditions, such as air, light soaking, and heating (65°C).