PREPARATION AND CHARACTERIZATION OF ZnS THIN FILMS USING CHEMICAL BATH DEPOSITION METHOD: EFFECTS OF DEPOSITION TIME AND THERMAL TREATMENT

摘要

This research focuses on zinc sulphide (ZnS) thin film preparation using the chemical bath deposition (CBD) method. The obtained product is to be used as the Cd-free buffer layer for CIGS solar cells. Zinc sulfate, thiourea, hydrazine, and ammonium hydroxide concentrations were carefully selected to synthesize the ZnS thin films. The deposition time and annealing effects on the optical and electrical properties were studied. Scanning electron micrographs showed that the film surface consisted of small uniform grains (about 40 nm in size) and were free of pin-hole defects. Field emission scanning electron micrographs reveals that the film thickness ranged from 50 to 120 nm. Hall Effect measurements indicated that the synthesized ZnS was an n-type semiconductor with a resistivity of 2 × 10~3 - 9 × 10~3 OMEGA cm. The as-deposited ZnS thin films exhibited high light transmittance, between 89.5% and 90.8%. The transmittance values decreased to 69.9%-71.2% after thermal annealing at 400°C for 420 min. The chemical composition of the resulting ZnS thin films are discussed in terms of the CBD process deposition time and thermal treatment.