A Comparative Study Between Nanocrystalline and Polycrystalline CdS Semiconductor Films

摘要

A chemical bath deposition technique was used to prepare nanocrystalline and polycrystalline CdS semiconductor films on glass/metal substrates at 28℃ and 80℃ respectively using 1M CdSO_4, 1M thiourea and 2M NH_4OH. The time duration for preparing bulk CdS film was 30 minutes whereas for nanocrystalline CdS film, the deposition time was varied from 2 to 90 minutes. The pH of the solution was also varied for nanocrystalline CdS film. Compositional analysis of the bulk CdS film indicated Cd:S = 50.4:49.6 whereas the nanocrystalline films showed sulfur deficiency Band gap values were estimated by optical absorption studies and found to be 2.4 eV for bulk CdS whereas for nanocrystalline CdS the band gap changed from 2.40 to 2.99 eV with decreasing time period of deposition. The fundamental absorption edge was seen to shift to lower wavelength for films prepared at lower deposition times in the case of nanocrystalline films. The photo effects were studied in the solar cell configuration as Ti/CdS/Na_2SO_3/Pt and the photovoltages were found to increase from the bulk value.