Electrical and optical properties of sputter-deposited cadmium sulfide thin films optimized by annealing temperature

Cadmium sulfide (CdS) is one of the most widely used materials as a window layer in heterojunction thin film solar cells. Sputtering method for the preparation of CdS thin film was employed for the mass-production of large-area deposited CdS thin films. The electrical and optical properties of sputter-deposited CdS thin films varied with the annealing temperature, which were caused by changes in phase composition, grain size, and stoichiometry of CdS thin films. The improved optical transmittance of 72.25% (at average thickness of 843.93 nm) and the optical band gap energy of 2.43 eV were obtained at the optimum annealing temperature of 400 °C. The resistivity below 103-order Ω cm and carrier concentration above 1016 carriers/cm3 are suitable for the requirements of window layers at this optimum annealing temperature.