Effect of film thickness on the solar cell performance of CBD grown CdS/PbS heterostructure

Abstract

CdS, PbS and CdS/PbS thin films were deposited onto glass and ITO substrates using chemical bath technique. The thickness of the CdS was varied by varying the deposition time and the influence of film thickness on structural, morphological, optical and electrical properties of the as-deposited films were investigated by XRD, SEM, UV–Vis–NIR spectroscopy and two-probe techniques. XRD analysis of CdS and PbS films have shown polycrystalline nature of the films with preferred orientation along (002) and (200) reflections. The grain size of the CdS film was found to increases with the film thickness. Scanning electron microscopic results of the CdS films have revealed smooth morphology and it has found to show increased particle size with the film thickness. Optical transmittance of the CdS thin films was found to decrease with the film thickness. The increase of deposition time is found to shift the band gap from 2.75 to 2.66 eV. Band gap of the PbS film is found to be 1.57 eV for a thickness of 0.89 µm. The photo-response studies done for CdS/PbS heterojunction solar cells have indicated that the film thickness has an influence on the cell efficiency. The observed enhancement in solar cell properties is attributed to the changes in the morphology, the crystalline quality and the optical properties caused by the increase of film thickness.