Effects of bath temperature on the properties of CdS and ZnS thin films deposited by Chemical bath deposition

CdS thin films were deposited by Chemical Bath Deposition (CBD) from a bath containing cadmium sulfate, thiourea and ammonium hydroxide. ZnS thin films were deposited by CBD from a bath containing zinc sulfate, thiourea, ammonium hydroxide and hydrazine. Effects of the bath temperature on the deposition processes and properties of CdS and ZnS thin films were investigated, and the difference of properties between CdS and ZnS thin films deposited in various bath temperatures was shown. It is demonstrated that the deposition rate increases with the increase of bath temperature, as well as the denseness of CdS and ZnS thin films. The band gaps of CdS and ZnS thin films get closer to their theoretic values with the increase of the bath temperature. The deposition rate of CdS is much higher than the deposition rate of ZnS when the bath temperature is above 70°C. It is also shown by the experimental results that the grain size and S/Cd ratio of CdS decreases with the increase of the bath temperature while the grain size and S/Zn ratio of ZnS increases. With high optical transmittance values for both CdS and ZnS thin films, more short-wavelength photons with high energy could pass through the ZnS thin films, which could enhance the efficiency of CIGS solar cells.