Theoretical Model and Device Performance of CuInS2 Thin Film Solar Cell

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Abstract
The capacitance vs. voltage characteristics and the current vs. voltage characteristics of the thin film solar cell consisting of a transparent conductive oxide/CdS/CuInS2 heterostructure are analyzed in terms of the theoretical device model where a very thin n-type CuInS2 layer exists on the top surface of the p-type absorber layer. The CuInS2 absorber layer is prepared by sulfurization of precursors deposited on a Mo-coated soda lime glass substrate or a Pt foil substrate. When the absorber layer is prepared on the former the heterostructure is an abrupt junction in which the net acceptor concentration of the absorber layer is of the order of 1016–1017 cm-3, but when prepared on the latter it is a linearly graded junction in which the gradient of the acceptor concentration lying in the order of 1020–1021 cm-4 is a decreasing function of precursor thickness. The highest open circuit voltage of 0.755 V is obtained in a solar cell that consists of the thickest absorber layer prepared on the latter and hence exhibits the lowest built-in electric field at the junction interface.