Efficient photoinduced charge injection from chemical bath deposited CdS into mesoporous TiO2 probed with time-resolved microwave conductivity

We use the contactless time-resolved microwave conductivity (TRMC) technique to investigate the photoconductance of CdS-coated mesoporous TiO2 and ZrO2. The CdS domains were grown directly on the surface of the oxide by a chemical bath deposition method. Mobile charge carriers are generated with a low yield following photoexcitation of US grown on ZrO2; there is no injection into the oxide and the short-lived photoconductance signal is attributed to the hole in CdS. In contrast, illumination of US domains grown on TiO2 results in very efficient electron injection into the TiO2 nanoparticles, producing long-lived charge carriers. We show that the quantum yield for electron injection into TiO2 per photon absorbed by the US sensitizer is close to unity. The photoconductance action spectrum follows the absorption of the CdS domains, which indicates that the charge injection efficiency does not depend on wavelength in the range where the US absorbs (425-550 nm).