Optimization of vapor post-deposition processing for evaporated CdS/CdTe solar cells

Abstract

The effects of thermal annealing in conjunction with CdCl2 vapor heat treatment on the properties of CdTe/CdS thin films and devices deposited by physical vapor deposition are reported. Results are compared for three treatment variations: high-temperature anneal only, high-temperature anneal followed by CdCl2 vapor heat treatment and CdCl2 vapor heat treatment only. X-ray diffraction, transmission electron microscopy and scanning electron microscopy show improved crystallographic properties of the CdTe film and reduced CdS/CdTe interdiffusion when a high-temperature anneal is used prior to CdCl2 treatment. The CdTe/CdS solar cells fabricated using an anneal at 550°C in argon prior to the CdCl2 vapor heat treatment exhibited improved electrical characteristics compared to cells fabricated with no anneal step, yielding an open-circuit voltage exceeding 850 mV. Copyright © 1999 John Wiley & Sons, Ltd.