Photosensitization of Nanoporous TiO2 Electrodes with InP Quantum Dots

Quantum dots (QDs) of InP strongly adsorb onto transparent, porous, nanocrystalline TiO2 electrodes prepared by sintering 200−250 Å diameter TiO2 colloidal particles. The interparticle space of the TiO2 electrodes is large enough to permit deep penetration of 65-Å InP QDs into the porous TiO2 film. The absorption of light increases linearly with the thickness of the TiO2 film indicating that the InP QDs are adsorbed homogeneously on the TiO2 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 TiO2 by InP QDs. The photocurrent action spectrum of the TiO2/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 TiO2, which was immersed in a I-/I3 - or hydroquinone/quinone acetonitrile solution, and a Pt counter electrode. These photoelectrochemical experiments show that electron transfer from InP QD into TiO2 nanoparticles occurs. p-Type InP/TiO2 electrodes are stable during illumination while n-type photocorrodes in an electrochemical cell.