The physical properties of semiconductors define to a great extent the performance of photoelectrochemical (PEC) cells. With a band gap of 1.7 eV, cadraium selenide is an attractive candidate as photoelectrode in PEC cells for the conversion of light into electricity. Polycrystalline films are used for low-cost cells. CdSe films are prepared on a titanium substrate by the electrocodeposition technique from a solution of SeO2, CdSO 4 and H2SO 4 in galvanostatic conditions, then annealed at 400 Β°C. Chemical modification of semiconductor surfaces by metal ions has been found to improve the performance of photoelectrodes. Zn ion incorporation on the CdSe film surface was achieved by dipping the film in aqueous solution of ZnSO4 followed by heating in air. The preparation conditions were optimized to give the best performance. The photovattaic activity of the films was studied with a polysulphide electrolyte using graphite as a counter electrode and a 200 Watt tungsten lamp as the light source.
Addition of Zn ions at the surface produces favourable states in band gap, enhancing charge transfer kinetics at the interface. On heating, Zn diffuses through grain boundaries, reducing recombination centres for majority carriers, thus increasing diffusion length and so photocurrenl. In the CdSe lattice, Zn replaces Cd ions which causes an increase in band gap since ZnSe has a band gap higher than CdSe. Hence a small amount of Zn reduces Isc due to an increase in band gap, but as the Zn concentration is increased, greater band belading is obtained, increasing Voc and improving overall performance.