Room‐Temperature Vapor Deposition of Cobalt Nitride Nanofilms for Mesoscopic and Perovskite Solar Cells

Organic/inorganic hybrid solar cells, typically mesoscopic and perovskite solar cells, are regarded as promising candidates to replace conventional silicon or thin film photovoltaics. There have been intensive investigations on the development of advanced materials for improved power conversion efficiencies, however, economical feasibilities and reliabilities of the organic/inorganic photovoltaics are yet to reach at a sufficient level for practical utilizations. In this study, cobalt nitride (CoN) nanofilms prepared by room-temperature vapor deposition in an inert N-2 atmosphere, which is a facile and highly reproducible procedure, are proposed as a low-cost counter electrode in mesoscopic dye-sensitized solar cells (DSCs) and a hole transport material in inverted planar perovskite solar cells (PSCs) for the first time. The CoN film successfully replaces conventional Pt in DSCs, resulting in a power conversion efficiency comparable to the ones based on Pt. In addition, PSCs employing the CoN manifest high efficiency even up to 15.0%, which is comparable to state-of-the-art performance in the cases of PSCs employing inorganic hole transporters. Furthermore, flexible solar cell applications of the CoN are performed in both mesoscopic and perovskite solar cells, verifying the advantages of the room-temperature deposition process and feasibilities of the CoN nanofilms in various fields.