Microwave Boosting of Interfacial Tunneling Electron Transfer in a Quantum Dot-Sensitized Photoelectrode

Microwaves (MWs) with a frequency of subgigahertz or multigigahertz can promote a rotation of polar molecules and a vibration of electric charges through an interaction with the alternating electric fields which comprise the MWs. The MWs can also promote the rotation of dipoles formed at the interface of Schottky junctions and semiconductor heterojunctions (e.g. pn junction), leading us to expect that photoinduced electron transfer reaction at the interface can be perturbed by the dipole rotation induced by MWs. In this paper, we successfully demonstrated that 2.45 GHz MWs can boost the photocurrents of FTO/TiO2 and FTO/TiO2/CdS electrodes, which are typically used electrode structures in quantum dot- or dyesensitized solar cells. From photoelectrochemical analysis using precisely controlled MW power and illuminant wavelength, a model is proposed in which the tunneling electron transfer reactions occurring in photoelectrodes are accelerated by MW-induced perturbations of the interfacial dipoles at the tunneling interfaces. The model proposed here would open the way for novel applications of MWs in the fields of photo-, electro-, and photoelectrocatalysis with the aim of solar energy conversion.