CuInS₂ Photocathodes with Atomic Gradation-Controlled (Ta,Mo)(O,S) Passivation Layers for Efficient...

An atomic gradient passivation layer, (Ta,Mo)(O,S), is designed to improve the charge transportation and photoelectrochemical activity of CuInS₂-based photoelectrodes. We found that Mo spontaneously diffused to the a-TaO layer during e-beam evaporation. This result indicates that the gradient profile of MoO/TaO is formed in the sublayer of (Ta,Mo)(O,S). To understand the atomic-gradation effects of the (Ta,Mo)(O,S) passive layer, the composition and (photo)electrochemical properties have been characterized in detail. When this atomic gradient-passive layer is applied to CuInS₂-based photocathodes, promising photocurrent and onset potential are seen without using Pt cocatalysts. This is one of the highest activities among reported CuInS₂ photocathodes, which are not combined with noble metal cocatalysts. Excellent photoelectrochemical activity of the photoelectrode can be mainly achieved by (1) the electron transient time improved due to the conductive Mo-incorporated TaO layer and (2) the boosted electrocatalytic activity by Mo(O,S) formation.