Effects of particles size distribution and occupied area of CdS photosensitizer on photovoltaic performance

Cadmium sulfide (CdS) photosensitizers were successfully formed on the mesoporous titania films using the successive ionic layer adsorption and reaction (SILAR) method in five cycles, and the effects of particles size distribution and their occupied surface area on the morphology, topography, optical property, and photovoltaic performance were investigated. Scanning electron microscope (SEM) images demonstrated that the increase in the number of SILAR cycles increased the number of deposited particles as well as their sizes so that the surface morphology after the third SILAR cycle changed from non-uniform particles to a uniform layer. The surface topography of all layers was hill-valley like, the roughness of which decreased as homogeneous layers formed. The absorbance spectra measured by UV-Vis spectrophotometer revealed that the absorbance spectra of the films increased and shifted towards longer wavelengths as the number of SILAR cycles increased, which is due to the increase in the particles size distribution. Photovoltaic measurements clarified that increase in the particles size distribution had the dominant effect up to the third SILAR cycle and increased the power conversion efficiency to a maximum of 4.65 %. However, as the occupied surface area increased due to the extreme formation of CdS particles and blocking of porosities in the mesoporous titania film, the efficiency dropped to 2.64 %.