Electrical and Optical Characterization of R.F.-Sputtered CdTe Thin Films

Four sets of R.F.-sputtered CdS/CdTe thin-film solar cells are activated through comparable treatment procedures. Two samples were rinsed into deionized water for an hour before CdCl₂ treatment and then activated in Ar or air ambient. The two others are normally treated and activated in Ar and air, respectively. The influence of water rinsing and annealing ambient on the electrical and optical properties of the films is investigated by current-voltage, field-emission scanning electron microscope, X-ray diffraction, and optical transmission spectroscopy. We examined water rinsing as a cheap and simple pretreatment step to modify the semiconductor surface and to obtain quality device. In this way, the fill factor of the cells that were rinsed into water before CdCl₂ activation was comparable with the one prepared without rinsing. There is a challenge between the effect of water and Ar on the electrical parameters of the cells. Water-rinsed cells annealed in Ar showed better properties than those that received no water rinsing. It seems that water reduces the negative effect of Ar annealing or parasitic diffusion of Cu into the semiconductor. The higher shunt resistance of the rinsed samples represents that water rinsing could passivate the surface defects and pinholes. The grain size, phase, and band gap of the thin films are extracted, analyzed, and compared with the as-deposited devices.