We developed transient photoreflectance (TPR) as an innovative time-resolved spectroscopic probe that can directly monitor charge transfer across semiconductor interfaces. This primary event leading to photochemical energy conversion is driven by a built-in internal electric field and produces a transient electric field at the interface that can be detected by following the modulation of the reflectance at the surface of the semiconductor. We employ TPR to study charge transfer at p-type gallium-indium phosphide (p-GaInP2), a well-known photocathode for hydrogen evolution. We monitored the formation and decay of the transient electric field that forms upon photoexcitation within bare p-GaInP2, p-GaInP2/platinum (Pt), and p-GaInP2/amorphous titania (TiO2) interfaces. We find that a built-in field at the p-GaInP2/TiO2 interface drives charge separation, similar to the field effects in the p-GaInP2/Pt photoelectrode, but that charge recombination of the former is hindered due its p-n nature compared to the Schottky nature of p-GaInP2/Pt. Our results provide a wealth of information about the role of amorphous TiO2 in the photoconversion process of TiO2-coated photoelectrodes and introduces a new technique to explore fundamental charge transfer processes at semiconductor interfaces.

Ultrafast photo-induced electric field at the surfaces of p-GaInP2 electrode

251st National Meeting (2016)

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