The effects of chlorine diffusion in doped CdS/CdTe photovoltaic cells grown by MOCVD

摘要

CdS/CdTe photovoltaic cells have been grown in a single process by MOCVD (Metal-Organic Chemical Vapour Deposition), with the CdS window layer doped n-type with Cl, and the CdTe absorber layer doped p-type with As. Incorporation of Cl into the CdTe layer via diffusion from the CdS layer is found to be detrimental to cell performance, considerably degrading the photocurrent. The diffusivity of Cl in CdTe is estimated by curve-fitting from calibrated SIMS data and is consistent with values from the literature measured by radiotracer methods. Diffusion mechanisms are dependent upon CdTe grain size, which in turn appears to be dependent upon VI/II ratio in the CdS layer. MOCVD is an ideal growth method for controlling the degree of Cl diffusion via growth temperatures, growth ambients and non-uniform doping methods such as removing the dopant species from the reaction mixture at a controlled distance from the junction.