Enhancement of opto-electrical properties in Co doped CdS–TiO2 nanocomposite thin film as photoanode for Semiconductor Sensitized Solar Cells (SSSCs)

Abstract

Cobalt doped CdS–TiO 2 nanocomposite thin films were coated on glass substrates by bottom up approaching methods. ZnS nanolayer over cobalt doped CdS–TiO 2 films act as a protective layer of CdS nanocrystal which enhances the photo stability. The structural, optical, electrical and surface morphological properties of ZnS-cobalt CdS–TiO 2 composite thin film were systematically evaluated. Structural analysis indicates that Co 2+ ions have been successfully incorporated in CdS site. The doping of cobalt in ZnS–CdS–TiO 2 film gives rise to an increase in the lattice parameter while the band gap decreased with increasing cobalt concentration. The bandgap of doped film decreases indicating the easy way of electron transfer from valence band to conduction band of CdS and TiO 2 . Surface morphological studies shows the diffusion of cobalt doped CdS nanoparticles into TiO 2 nanoporous structure of the composite film . The emission peaks in photoluminescence spectrum of ZnS-cobalt CdS–TiO 2 film proved the clear interaction of cobalt dopant with CdS nanocrystals. An enhancement in conductivity was observed due to incorporation of cobalt in CdS site and the resistance value (∼47%) was significantly decreased for cobalt doped CdS under illumination condition. Electrical analysis proved that the doped film is preferred as conductive electrode in solar cells than undoped film. • Cobalt doped CdS–TiO 2 composite thin films were synthesized by simple wet chemical method. • Interlocked CdS nanocrystals observed in SEM analysis, facilitate easy penetration into TiO 2 nanoporous structure of the composite film. • The doped film exhibit shifting of absorption edge towards longer wavelength (red shift), indicates decreased optical band gap. • The doped film shows superior electrical performance due to decreased resistance, preferred as conductive electrode in solar cells.