An evolution to Bismuth dopant concentration on properties of CdSe films for solar cell appliances

Abstract

The deliberated introduction of dopant to the crystalline host lattice is a promising approach towards the adjustment of physical properties. The present work deals with the influence of Bi dopant concentration on crystallographic, optical, topographical and electrical features of CdSe films for absorber layer applications to solar cells. Herein, the deposition of undoped and Bi doped CdSe films having 1%, 3% and 5% Bi dopant concentration is carried out via resistive heating thermal evaporation method. The crystallographic patterns reveal to the polycrystalline nature of films with occurrence of major reflection along (111) plane of cubic CdSe system where the intensity of this peak is substantially altered with Bi dopant. The crystallite size and strain of the CdSe films are appeared in range of 32–53 nm and 3.01 × 10−3–5.06 × 10−3, respectively upon changing the Bi doping. Optical study indicates the manifestation of strong absorption in visible region of spectra and fluctuation in absorbance of CdSe films with change in Bi dopant concentration. The optical band gap of undoped and Bi doped CdSe films is obtained in 1.61–1.69 eV range. Electrical assessment of films points towards creation of Ohmic contacts where the conductivity of films is improved at 1% Bi doping and decreased at higher doping. All the films show spherical shaped grains with variable density where the grain size obtained from AFM analysis is varied from 24 nm to 40 nm with Bi dopant concentration. Hence, the concentration of trivalent Bi dopant plays a pivotal role in modulation of properties of CdSe films for absorber layer appliances.