Near infrared luminescence of CdS:Cu thin films prepared by chemical bath deposition

Abstract

CdS is an n-type heterojunction partner of p-type CdTe or CuIn(Ga)Se2 absorber layer in polycrystalline heterostructure solar cells. The best solar cells based on Cu(InGa)Se2 (CIGS) absorbers are achieved by using a very thin (50 nm) CdS buffer layer deposited by chemical bath deposition (CBD) [1].The conductivity of the CdS window layer has to be optimized in order to achieve high efficiency of the devices. It is well known that the conductivity of the CdS films is sensitive to heat treatment [2]. Separate measurement of the conductivity of the layers in the multilayer structures is very difficult, but the change of optical absorption or photoluminescence spectra can indicate the impurity levels of the layers. High intensity infrared luminescence, indicate acceptor like deep levels, which compensate the electron concentration, and decrease the conductivity of the CdS layers. In this work, CdS thin films prepared by chemical bath deposition have been characterized by infrared (IR) luminescence, optical transmission, and photoconductive response measurements