Effect of Thickness on the Film Properties of Spray Deposited Copper Indium Sulfide Thin Films by Ultrasonic Impact Nozzle

Abstract

In this study, copper-indium-sulfide (CuInS₂) thin films were deposited on soda lime glass substrates using ultrasonic spray pyrolysis (USP) technique from the aqueous solution of Copper(II)chloride-dehydrate (CuCl₂), indium(III)chloride (InCl₃) and thiourea (NH₂CSNH₂). To investigate the effect of film thickness, different solution amounts were sprayed. As expected, the thickness of the films increased with increasing the amount of solution used. It has been obtained that thickness of the CuInS₂ absorber layer is critical for structural, morphological and optical properties. Crystal structure of the spray-deposited films was confirmed using X-ray Diffraction (XRD) analysis. The crystallite size of the films was ranging between 68 and 147 nm. X-ray photoelectron spectroscopy (XPS) study revealed that Cu concentration in the films increased by increasing the solution amount. Surface morphology of the films was investigated via scanning electron microscope (SEM). All sprayed films were defect free. Moreover, Cu rich-island formation was observed on the surface of CuInS₂ films sprayed using solutions more than 20 ml. Optical band gap energy of the films decreased from 2.85 to 1.40 eV with increasing the solution amount. As a result, thin films deposited using 30 ml solution was superior to others in terms of structural and optical properties. Moreover, it is very important to mention here that the ultrasonic impact nozzle used in this study enabled using very little amount of solution (0.015 ml/mm²), which is approximately 10 times lower than solution reported previously. This promising result can be the key for large-area manufacturing of CuInS₂ based solar cells.