ELECTROLESS-CHEMICAL GROWTH OF ZnSe-ZnO THIN FILMS FOR SOLAR CELL APPLICATION

摘要

The growth of films with mixed ZnSe and ZnO composition from aqueous solution is studied with a quartz crystal microbalance (QCM). A sequence of electrochemical and chemical steps take place in the mechanism of growth on metallic substrates (Pt, Au). There is first an induction period of chemical nature which ends up with the formation of ZnSe particles in the bulk solution. These particles activate the growth of the film by an electroless deposition process which gives rise to deposition of ZnO and ZnSe. The net electroless process comprises oxidation of hydrazine added in the bath, reduction of water, and the deposition of the film with Zn(Se_x,O_y) composition. Selenourea adsorbed onto the substrate surface appears to have a catalytic effect in this process. The deceleration of the electroless deposition reaction after some minutes is attributed to the decomposition of the catalytic selenourea film. Hence, the growth of the film continues by a chemical mechanism consisting in the reaction of the decomposition product of selenourea (SeSO_3~(2-)) and the zinc-ammonia complex, which gives rise to deposition of layers with ZnSe composition predominantly. Finally, the growth of the film attains a regime independent on the substrate surface, which indicates deposition of ZnSe particles formed in the solution. The resulting film has a mixed zinc oxide-selenide composition with predominant oxide proportion in the layers close to the substrate, and increasing the selenide proportion above.