It is appealing to harvest solar energy directly into chemical bonds with photo-electrochemical (PEC) cells—for example, by splitting water into hydrogen (H2) and oxygen (O2), as first demonstrated by Fujishima and Honda. Achieving the highest possible efficiency requires rapid transfer of the charge carriers generated by semiconductor photoabsorbers to the catalysts for H2 and O2 evolution. Long-term stability requires protection layers for the semiconductors against strong acid or base. Direct experimental observation of charge carrier dynamics at these complex interfaces, which is critical for optimization, has been a major challenge. On page 1061 of this issue, Y. Yang et al. show how transient photoreflectance spectroscopy can reveal information about the carrier dynamics and the electric field near the semiconductor surface.
http://www.sciencemag.org/content/350/6264/1030.full
Semiconductor interfacial carrier dynamics via photoinduced electric fieldsSolar photoconversion in semiconductors is driven by charge separation at the interface of the semiconductor and contacting layers. Here we demonstrate that time-resolved photoinduced reflectance from a semiconductor captures interfacial carrier dynamics. We applied this transient photoreflectance method to study charge transfer at p-type gallium-indium phosphide (p-GaInP2) interfaces critically important to solar-driven water splitting. We monitored the formation and decay of transient electric fields that form upon photoexcitation within bare p-GaInP2, p-GaInP2/platinum (Pt), and p-GaInP2/amorphous titania (TiO2) interfaces. The data show that a field at both the p-GaInP2/Pt and p-GaInP2/TiO2 interfaces drives charge separation. Additionally, the charge recombination rate at the p-GaInP2/TiO2 interface is greatly reduced owing to its p-n nature, compared with the Schottky nature of the p-GaInP2/Pt interface.
Science 27 November 2015:
Vol. 350 no. 6264 pp. 1061-1065
DOI: 10.1126/science.aad3459
http://www.sciencemag.org/content/350/6264/1061
