Photoelectrochemical Properties of Particulate CuGaSe2 and CuIn0.7Ga0.3Se2 Photocathodes in Nonaqueous Electrolyte

The photoelectrochemical (PEC) properties of particulate CuGaSe2 (CGSe) and CuIn0.7Ga0.3Se2 (CIGS) photocathodes were evaluated in an acetonitrile electrolyte containing iron(III) acetylacetonate (Fe(acac)3) under simulated sunlight illumination, and compared to that in a typical aqueous electrolyte. The particulate CGSe and CIGS photocathodes can generate higher photovoltages, which is a more positive onset potential than the hydrogen evolution in an aqueous electrolyte possibly due to the facile one-electron reduction of Fe(acac)3, while the cathodic photocurrent decreased due to light shielding by the colored nonaqueous electrolyte. Indeed, the incident-photon-to-current conversion efficiencies (IPCEs) of the photocathode evidently decreased in the wavelength region of 400–600 nm, where the Fe(acac)3 acetonitrile electrolyte shows an intense light absorption. The CIGS photocathode generates a higher cathodic photocurrent than the CGSe during hydrogen evolution from the aqueous electrolyte, while the CGSe exhibits superior PEC performances to CIGS in the nonaqueous electrolyte, which can be explained by the energy level of the conduction band minimum (CBM) of CGSe and CIGS compared to the reduction potential for Fe(acac)3. Finally, the two-electrode PEC-voltaic (PECV) cell consisting of the CGSe photocathode and Pt anode demonstrated a stable generated photovoltage by a one-step photoexcitation process.