CuInS2quantum dots coated with CdS as high-performance sensitizers for TiO2electrodes in photoelectrochemical cells

Abstract

We report on a high-performance photoelectrode consisting of a nanocrystalline TiO₂ film co-sensitized with CuInS₂ quantum dots (QDs) and CdS layers. In this photoelectrode, solvothermally synthesized CuInS₂ QDs, monodispersed at sizes of 3.5 and 4.3 nm, are attached to a TiO₂ substrate by means of a bifunctional linker, before it is coated with an in situ growth of CdS followed by successive ionic layer adsorption and reaction. The QDs has a high-level conduction band for the efficient injection of electrons into TiO₂. The CdS coating provides high surface coverage to prevent interfacial recombination and releases the quantum confinement of the QDs, resulting in band gap reduction from 2.10–1.80 eV and 1.94–1.76 eV for the 3.5 and 4.3 nm QDs, respectively. With AM 1.5G illumination at 100 mW cm⁻², this heterostructural electrode exhibits a saturated photocurrent as high as 16 mA cm⁻² in a polysulfide solution. Systematic analysis suggests that the photocurrent resulting from the CuInS₂ QDs is increased by more than 100%, thanks to the CdS coating. This coating extends the absorption spectra of the QDs and facilitates charge separation by scavenging photogenerated holes in the valence band of the QDs.