Rethinking Electrochemical Deposition of Nickel Oxide for Photovoltaic Applications

A thin layer of sputtered or wet-processed nickel oxide (NiOx) is often used to fabricate perovskite solar cells (PSCs). Remarkably, NiOx can also be deposited by a recently developed electrochemical method, which is considered promising due to its short processing time, absence of high-vacuum conditions, and ease of manufacturing. Such electrochemically deposited NiOx (eleNiOx) is obtained by applying an electric bias to the front electrode of a PSC or perovskite solar module (PSM). Therefore, the electrode sheet resistance affects the current distribution through it, creating a gradient in the amount of charge provided for the electrochemical reaction. Consequently, this leads to the inhomogeneity in the formed eleNiOx, which has numerous implications on the final photovoltaic performance of PSMs. In this work, the interdependencies between the electrode sheet resistance, current distribution, eleNiOx thickness gradient, and the caused power losses of large area PSMs are discussed. By coupling the experimental findings with our numerical simulations, it is found that heterogeneity in surface potential of even small-sized modules can lead to severe differences in local eleNiOx thickness and photovoltaic performance. Therefore the potential drop across the front electrode is an inherent problem of this deposition method and potential approaches are proposed to minimize it.