Computational fluid dynamics (CFD) modeling for CdTe solar cell manufacturing

Abstract

The CdTe solar cell manufacturing process developed at Colorado State University used a vapor source that utilized infrared heating lamps as the heating source. This was used in the initial research system that was used to develop the inline CdTe solar cell manufacturing method used in industry. This system has since been redesigned to improve its ability to function as a more versatile research tool. This thesis focuses on the modeling efforts used in the development and understanding of an embedded NiCr heating unit for the vapor source. The traditional infrared heating lamps, while effective, were inefficient. A new design consisting of a NiCr heating element embedded in to the graphite deposition crucible, was developed as a more efficient and robust replacement to the infrared lamps. Four distinct models of increasing complexity were developed using the heat transfer modeling capabilities of ANSYS Fluent. The first two models helped to determine the overall thermal uniformity and the ability of the new heating designs ability to reach the needed temperatures of the deposition processes. The third model discussed in this thesis, aided in the development of the top heater that would maintain the desired steady state temperature at the process station used to deposit CdS films. The final model developed contains a higher level of detail used to determine the validity of previous assumptions and to gain an understanding of the internal temperature profile of the completed source. This modeling effort was extended to the system used in industry. The experimental data was compared to the modeled data verifying the model accuracy. The calculated temperatures were within 2.5% of the measured temperatures. The modeling efforts of both the CSU and Abound Solar deposition systems have proved the usefulness of CFD modeling as an important tool to equipment development and characterization.