The Influence of Grain Boundary Diffusion on the Electro-Optical Properties of CdTe/CdS Solar Cells

We report on a study of the effects of diffusion of metals through polycyrstalline CdTe thin films. The metals Ni, Pd, Cu, Cr, and Te are deposited onto the back surface of 10-μm thick CdTe/CdS device structures using room-temperature evaporation. We found that four out of the five metals produce significant changes in the photoluminescence (PL) of the near-junction CdTe material. These changes are explained in terms of spatial variations of the photoexcited carrier distribution and spatial variations in the sulfur composition of the CdTeS alloy material near the CdTeS interface. The changes in carrier distribution appear to be associated with band bending and electric fields induced by diffusion of the metals to the CdTe/CdS interface. In addition to PL measurements, we have also utilized a technique for detaching the CdTe film from the CdS/TCO/glass superstrate to directly access the front surface of the CdTe absorber layer. We have used secondary ion mass spectroscopy to measure the metal diffusion profiles from this interface.