Zinc doped polycrystalline CdSe films for solar energy conversion

• Published in: Materials science & engineering. B, Solid-state materials for advanced technology Solid-state materials for advanced technology, 1995, Vol.35 (1), p.493-496
• Main Author: Ramrakhiani, Meera
• Format: Article
• Language: English
• Subjects: cadmium selenide; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Electrical properties of specific thin films; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Exact sciences and technology; Ii-vi semiconductors; Photoelectrochemical cells; Physics; Q1; Semiconductors; Solar energy; Titanium; Zinc
• ISSN: 0921-5107; 1873-4944
• DOI: 10.1016/0921-5107(95)01435-7

The physical properties of semiconductors define to a great extent the performance of photoelectrochemical (PEC) cells. With a band gap of 1.7 eV, cadmium 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 SeO 2, CdSO 4 and H 2SO 4 in galvanostatic conditions, then annealed at 400 °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 ZnSO 4 followed by heating in air. The preparation conditions were optimized to give the best performance. The photovaltaic 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 photocurrent. 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 I sc due to an increase in band gap, but as the Zn concentration is increased, greater band bending is obtained, increasing V oc and improving overall performance.