Chang-Ming, Jiang. Reyes-Lillo, Sebastian ELiang, YufengLiu, Yi-ShengLiu, GuijiM. Toma, FrancescaPrendergast, DavidD. Sharp, IanK. Cooper, Jason2022-10-172022-10-172019-04Chemistry of Materials Open AccessVolume 31, Issue 7, Pages 2524 - 25349 April 201908974756https://repositorio.unab.cl/xmlui/handle/ria/24299The path to realizing low-cost, stable, and earth-abundant photoelectrodes can be enabled through a detailed understanding of the optoelectronic properties of these materials by combining theory and experimental techniques. Of the limited set of oxide photocathode materials currently available, CuFeO2 has emerged as a promising candidate warranting detailed attention. In this work, highly compact thin films of rhombohedral (3R) CuFeO2 were prepared via reactive co-sputtering. Despite its 1.43 eV indirect band gap, a cathodic photocurrent of 0.85 mA/cm2 was obtained at 0.4 V versus reversible hydrogen electrode in the presence of a sacrificial electron acceptor. This unexpected performance was related to inefficient bulk charge separation because of the ultrafast (<1 ps) self-trapping of photogenerated free carriers. The electronic structure of 3R-CuFeO2 was elucidated through a combination of optical and X-ray spectroscopic techniques and further complemented by first-principles computational methods including a many-body approach for computing the O K-edge X-ray absorption spectrum. Through resonant inelastic X-ray scattering spectroscopy, the visible absorption edges of CuFeO2 were found to correspond to Cu ↠Fe metal-to-metal charge transfer, which exhibits a high propensity toward self-trapping. Findings of the present work enable us to understand the performance bottlenecks of CuFeO2 photocathodes and suggest feasible strategies for improving material limitations. © 2019 American Chemical Society.enAbsorption spectroscopy; Charge transfer; Computation theory; Electronic structure; Energy gap; Field emission cathodes; Photocathodes; Reactive sputtering; Sputter deposition; X ray absorption; X ray scatteringArtículo