Evaluation of electroactive surface area of CdSe nanoparticles on wide bandgap oxides (TiO2, ZnO) by cadmium underpotential deposition

Underpotential deposition of cadmium was applied for in situ determination of electroactive surface area (ESA) of CdSe nanoparticles deposited by successive ionic layer adsorption and reaction (SILAR) onto TiO₂ nanotubes and porous ZnO films. The sensitized photocurrent on CdSe/TiO₂ and CdSe/ZnO electrodes was normalized for ESA, and the ESA normalized photocurrent was compared with the photocurrent normalized for geometric area of electrodes. Significantly different types of dependences were observed with the two methods of normalization for the surface area. The efficiency of CdSe as sensitizer appeared to be higher on ZnO when normalized for CdSe ESA, though the photocurrent normalized for geometric area of electrode was an order of magnitude higher on CdSe/TiO₂ electrodes. Also, notable maxima in the photocurrent dependences on the number of SILAR cycles disappeared after the normalization for the ESA, showing a gradual increase in the efficiency of the sensitizer unit surface area with the number of SILAR cycles. This simple experimental procedure can be a helpful tool in the investigation and development of quantum dot-sensitized solar cells.