Tunable Photoelectrochemical Properties of Chalcopyrite AgInS₂ Nanoparticles Size-Controlled with a Photoetching Technique

Abstract

Size-selective photoetching enabled precise size control of chalcopyrite AgInS2 nanoparticles in a basic aqueous solution containing ammonia by selecting the wavelength of monochromatic irradiation light in the range between 650 and 520 nm. The energy gap of the photoetched particles was enlarged from 1.8 to 2.4 eV with a decrease in particle size from 5.1 to 2.7 nm due to the quantum size effect, while the crystal structure and chemical composition of the particles were unchanged after the photoetching processes. AgInS2 nanoparticle-immobilized electrodes exhibited an anodic photocurrent similar to that of n-type semiconductors, the onset potential of which was negatively shifted with a decrease in particle size. Potentials of the conduction band edge (ECB) and the valence band edge (EVB) of AgInS2 nanoparticles were estimated from their photoelectrochemical measurements, and they exhibited remarkable size dependence: with a decrease in particle size from 5.1 to 2.7 nm, ECB was shifted negatively from −0.6 to −1.0 V vs Ag/AgCl, accompanied by a positive shift of EVB from 1.3 to 1.7 V vs Ag/AgCl.