CZTS/CdS: interface properties and band alignment study towards photovoltaic applications

Abstract

Thin films of CZTS and CdS have been synthesized at optimized process parameters using radio frequency sputtering. These films were characterized using the variety of techniques for their structural, morphology, electric transport, and optical properties. Low angle-XRD and Raman spectroscopy analysis revealed the formation of a single phase of kesterite-CZTS and highly pure hexagonal CdS films. The HR-TEM analysis shows that both CZTS and CdS films are highly crystalline. The optical band gap was found to be ∼ 1.5 eV for CZTS and ∼ 2. 35 eV for CdS films. The cyclic voltammetry (CV) investigations on drop-casted optimized CZTS and CdS on Au electrodes have been performed to determine electrochemical band gap as well as band edge parameters. It has been observed that electrochemical band gap values from CV measurements are in good agreement with the optical band gap values estimated using UV–Visible spectroscopy. Finally, values of conduction band offset (CBO) and valence band offset have been calculated using band edge parameters which are measured by CV analysis. Band bending induced by CdS/CZTS hetero-junction formation leads to spike like CBO of ∼ 0.55 eV which can suitable for solar cells and expected to enhance photovoltaic performance.