Photochemical Charge Separation in Nanocrystal Photocatalyst FilmsInsights from Surface Photovoltage

ABSTRACT: Photochemical charge generation, separation, and transport at nano-crystal interfaces are central to photoelectrochemical water splitting, a pathway to hydrogen from solar energy. Here, we use surface photovoltage spectroscopy to probe these processes in nanocrystal films of HCa2Nb3O10, a proven photocatalyst. Charge injection from the nanoparticles into the gold support can be observed, as well as oxidation and reduction of methanol and oxygen adsorbates on the nanosheet films. The measured photovoltage depends on the illumination intensity and substrate material, and it varies with illumination time and with film thickness. The proposed model predicts that the photovoltage is limited by the built-in potential of the nanosheet−metal junction, that is, the difference of Fermi energies in the two materials. The ability to measure and understand these light-induced charge separation processes in easy-to-fabricate films will promote the development of nanocrystal applications in photoelectrochemical cells, photovoltaics, and photocatalysts. SECTION: Energy Conversion and Storage; Energy and Charge Transport Photochemical charge separation on the nanoscale is ofcentral importance for solar energy conversion with inorganic nanocrystals.1 Analytical methods for this proces