Modification of the optoelectronic properties of sprayed In2S3 thin films by indium diffusion for application as buffer layer in CZTS based solar cell

Abstract

In this report the authors discuss the effect of diffusion of metallic indium on the optoelectronic proper- ties of chemical spray deposited indium sulfide (In2S3) thin films which are prospective candidates for buffer layer application in thin film solar cells. Thin layers of metallic indium having different thicknesses were diffused into the films by evaporating different quantities of indium using vacuum evaporation technique followed by annealing. ‘In’ diffusion was done with an aim to reduce resistivity and improve the crystallinity to ensure better carrier collection. X-ray diffraction, X-ray photoelectron spectroscopy, optical absorption, photoluminescence and electrical studies were performed on the films. Analysis indi- cated that crystallinity attained a maximum for an optimum ‘In’ diffusion and then showed a retracing nature. Resistivity was found to decrease drastically from 2.3Â 105 O cm [pristine] to 4.7 O cm [for the optimum indium diffused samples]. Using the optimized In2S3 layer and copper zinc tin sulfide (CZTS) deposited using chemical spray pyrolysis, a heterojunction device was successfully fabricated with a con- version efficiency of 1.85% and fill factor of 52%. The optimum quantity of indium to be diffused depends on the thickness of the In2S3 thin film.