Interfacial carrier kinetics in Cu 2 O photocathodes for bias-free solar water splitting Keming Li 1 , Jinshui Cheng 2 , Daniele Benetti 1 , James R. Durrant 1 , Jingshan Luo 2 1 Department of Chemistry & Centre for Processable Electronics (CPE), Imperial College London, W12 0BZ, UK, 2 Institute of Photoelectronic Thin Film Devices and Technology, Nankai University, Tianjin, 300350, China The global pursuit of sustainable hydrogen production has intensified interest in photoelectrochemical (PEC) water splitting, with Cu 2 O emerging as a promising photocathode due to its ideal bandgap and favorable band alignment for H 2 evolution. Although Cu 2 O photocathodes demonstrate excellent PEC performance in bias-free tandem integration with photovoltaic components, the conventional Au back contact poses significant limitations: its poor optical transmittance restricts rear absorber illumination, and its lack of charge selectivity facilitates interfacial recombination, both of which constrain the achievable photovoltage. Here, we introduce magnetron- sputtered Cu 2 O (MS-Cu 2 O) as a transparent back contact, which significantly enhances both the fill factor and transmittance compared to conventional Au contacts. Ultrafast transient absorption spectroscopy (TAS) reveals that the backside homojunction at the interface between electrodeposited Cu 2 O (ED-Cu 2 O) and MS- Cu 2 O establishes a favorable energy landscape that facilitates efficient hole extraction to the back contact while simultaneously blocking undesired electron backflow. This selective carrier modulation suppresses interfacial recombination losses, resulting in a long-lived carrier population and enhanced charge collection efficiency.
P50
© The Author(s), 2025
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