Enhanced multifunctional attributes of Tellurium incorporated CuGaS2 thin films employing spray pyrolysis route

Abstract

CuGaS2 (CGS) chalcopyrite semiconductor is a promising candidate for thin-film based photovoltaic devices due to its exceptional optical absorption coefficient and flexibility in tuning the optical bandgap. Unfortunately, though, desorption of sulfur (S) atoms during deposition of CGS thin films at elevated temperatures results in the formation of defects and alters the material attributes. Post sulfurization may minimize S deficit, but it is still challenging to control S content due to its high vapour pressure. Therefore, this work investigates the effect of Tellurium (Te) doping during deposition on CGS’s crystallinity and optical properties, expecting relatively low vapour pressure of Te to stabilize the CGS structure. X-ray diffraction reveals the formation of a tetragonal phase indicating a better crystallinity and an enhanced crystallite size. Electrical mobility increased with Te doping, potentially due to the reduced grain boundary scattering with increased crystallite size. The optical bandgap energy of the deposited material decreases from 2.45 eV to 2.00 eV with increasing the concentration of dopant. These results make the CuGa(S,Te)2 a potential absorber material with a tuneable bandgap for solar cell application in a high energy spectrum.