STRUCTURE AND GROWTH-KINETICS OF ELECTRODEPOSITED CDS THIN-FILMS FOR SOLAR-CELL APPLICATIONS

An organic electrochemical deposition technique for preparation of coherent and uniform CdS thin films with oriented crystalline structure is described. Under the conditions of high Cd2+ ion concentrations (> 0.075M) and high deposition currents (>62; 5 mA/cm2) void free films with crystallite sizes ∼ 0.5 μm having a preferred c-axis orientation are deposited for solar cell application. The film composition is stoichiometric and invariant with deposition variables. Deposition occurs by a cathodic reaction of deposited Cd with S through a bielectronic exchange process. On deposition from low Cd electrolytes (< 0.055M), this changes to an 8 3 electron process. Non-linear growth kinetic behaviour reveals importance of extrinsic reactions like physico-adsorption involving S82- and S62- ionic species in determining the structural development of CdS films. CdS film resistivity ranges between 107 and 104 ω cm and depends on film thickness and electrolytic ratio of Cd and S ions. © 1990.