Synthesis and characterization of CdS nanoparticles decorated TiO₂ matrix for an efficient N3 based dye sensitized solar cell (DSSC)

The conventional dye sensitized solar cell (DSSC) comprise of mostly the titania matrix sensitized with absorber dye molecules acting as light energy scavengers. The present investigation deals with formulating CdS–TiO₂ conjugate matrix for the DSSC system using N3 dye sensitizer. TiO₂ nanoparticles (NPs) were pasted on FTO glass substrate and thin film of CdS was coated on titania matrix by chemical bath deposition technique using precursors cadmium acetate and thiourea. The differential absorbance spectra of the CdS–TiO₂ conjugate system shows sharp absorption edges around 345–500 nm, corresponding to band gap energies in the region 3.59 and 2.47 eV respectively, indicative of formation of two distinguishable energy region for the existence of the nano crystallites of both TiO₂ and CdS. The shift in Raman bands was also observed with the incorporation of CdS in TiO₂ matrix. XRD data confirms the formation of crystalline CdS nanoparticles. The FE–SEM images revealed that the TiO₂ particles are spherical and monodispersed having diameter in the range 20–30 nm and embedded with CdSNPs of average particle size 10–15 nm. The performance characteristics of the synthesized films towards photovoltaic behavior were studied with the record of short circuit currents through J–V measurement using N3 absorber dye and the I⁻/I₃ ⁻ electrolyte under 30 mW cm⁻² light intensity. An effective increase of efficiency is observed with the CdS modified TiO₂ matrix compared to the bare TiO₂ in the DSSC system and a maximum photo-conversion efficiency of 7.5 % was obtained with the optimized dye loading. Impedance spectroscopic measurements give important information about the interfacial electron injection and recombination dynamics of the device. The incident photon-to-current conversion efficiency measurements show that both the absorbers CdS and N3 dye, contribute to the cell performance.