Photosensitization of Nanoporous TiO₂ Electrodes with InP Quantum Dots

Abstract

Quantum dots (QDs) of InP strongly adsorb onto transparent, porous, nanocrystalline TiO 2 electrodes prepared by sintering 200−250 Å diameter TiO 2 colloidal particles. The interparticle space of the TiO 2 electrodes is large enough to permit deep penetration of 65-Å InP QDs into the porous TiO 2 film. The absorption of light increases linearly with the thickness of the TiO 2 film indicating that the InP QDs are adsorbed homogeneously on the TiO 2 surface. We found that large particles adsorb better than smaller ones probably due to less hindrance by the stabilizer. The solid films exhibit strong photoconductivity in the visible region indicating photosensitization of TiO 2 by InP QDs. The photocurrent action spectrum of the TiO 2 /InP QD film at a potential of +1 V is consistent with the absorption spectrum of the InP QDs. A photoelectrochemical cell was formed that consisted of p-type InP QDs loaded on TiO 2, which was immersed in a I - /I 3 - or hydroquinone/quinone acetonitrile solution, and a Pt counter electrode. These photoelectrochemical experiments show that electron transfer from InP QD into TiO 2 nanoparticles occurs. p-Type InP/TiO 2 electrodes are stable during illumination while n-type photocorrodes in an electrochemical cell.