Synthesis, characterization and dye-sensitized solar cell application of Zinc oxide based coaxial core-shell heterostructure

In the present work, the ZnO/CdS coaxial core-shell heterostructure has been synthesized on indium doped tin oxide glass substrate using chemical solution methods and further it is used as photoanode in the DSSC application. Four samples with different concentration of sulphur source were prepared. The approximate crystallite size of 22 nm for ZnO and 18 nm for CdS has been obtained as analyzed from x-ray diffraction data. FESEM and HRTEM images confirm the formation of CdS shell on ZnO nanorods with a width below 100 nanometer. UV-visible spectroscopy and photoluminescence spectroscopy were used to examine the optical response revealing the fact that bandgap reduction and a small redshift takes place for core-shell structure as compared to bare ZnO nanorods array. The J-V characterization was performed to study the photovoltaic response. Improved efficiency was observed for core-shell ZnO/CdS heterostructure (3.66%) as compared to bare ZnO nanorods based DSSCs (0.70%). This improvement is due to increased current density caused by reduced recombination of photogenerated electron hole pairs. This reduced recombination is achieved by two factors, one is the formation of type two core-shell heterostructure and second is increasing sulphur concentration in shell structure.