Publication date: 15th December 2025
Wide-gap chalcogenides without In, such as CuGaSe2 and CuGa3Se5, serve as excellent photocathodes for unassisted water splitting. These thin films cover 86% and 68% of the maximum theoretical photocurrents with band gaps of 1.68 and 1.85 eV, respectively [1]. However, Fermi level pinning is one of the major challenges that hinders the charge transfer at the semiconductor/electrolyte junction, leading to overpotentials between Eon and Efb. Over the years, Ag incorporation has gained focus to address the challenges in PEC (Photoelectrochemical), as partial substitution of Cu by Ag deepens the VBM and reduces the formation of Cu-deficient phases. We prepared wide-band-gap AgxCu1-xInGaSe2 thin film photocathodes via a three-stage co-evaporation process. We investigated different compositions where [Ag]/[Ag]+[Cu] (AAC) = 20% emerges as highly efficient thin film in both PV (η = 11.56%) and PEC (Jph= 24.08 mA/cm2), and also examine the influence of (AAC) and [Ga]/[Ga]/[In] (GGI) depth profiles on both PEC and PV cells. To enhance the PEC properties, we further modify the surface to form a p-n junction on the surface of the electrode, and also study the impact of catalyst layers. Finally, we present the experimental results with improved onset potentials and photocurrent density, for both with and without surface modification.
Authors acknowledge the support of Prof. Dr. Roland Scheer (MLU) and his team members Dr. Torsten Hölscher and Julia Horstmann for sample preparation.
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