The crystal structure of CdS-CdTe thin film heterojunction solar cells

A detailed structural analysis of electrodeposited CdS-CdTe thin him hetero junction solar cells was undertaken. X-ray diffraction and Rutherford backs cattering spectrometry were used to provide stoichiometric and microcrystal line data at increasing depths through the CdTe and CdS films. A model of t he nature and extent of interdiffusion caused by a post deposition anneal i s developed ii region in both preannealed and post-annealed samples which p ossesses a significantly different microstructure to that of the bulk CdTe, was identified. Within this region a stoichiometric gradient occurs and th e grain size and preferred orientation decrease with increasing depth. Maxi mum CdTe film stress (post anneal) is estimated to be 140 MPa close to the interface and a shift in optical band gap of 6 x 10(-3) eV was also determi ned from structural measurements. We provide evidence that sulphur diffusio n into CdTe is structurally rather than thermodynamically Limited within th ese systems. (C) 1999 Elsevier Science S.A. All rights reserved.