Graduation Year

2003

Document Type

Thesis

Degree

M.S.E.E.

Degree Granting Department

Electrical Engineering

Major Professor

Ferekides, Christos S.

Keywords

vacuum processing, thin films, ii-vi semiconductors, photovoltaics

Abstract

With CdTe based photovoltaics developed by close spaced sublimation reaching efficiencies of over 16%, commercialization of this technology draws serious attention. Today large area industrial modules have not been able to produce the same performance of their laboratory counterparts. This work provides a means for understanding the various technical challenges in developing an effective deposition technology for large area processing. The submodule process investigated provides a model for continuous and sequential processing of subsequent films. The system has a unique design and constructed with the provision for a moving transport module for the substrate transport. The process was developed to deposit large area CdTe (3 x 3 sq. inch) and provides valuable insights for the development of a large area deposition system. Upon optimizing the system for reproducibility, proper deposition conditions were established.

Films deposited under various conditions were studied to improve our understanding of the influence of processing conditions on device performance. The key advantage of this technique over others is its high deposition rate, simplicity of operation and high conversion efficiency. Typical deposition times were two minutes and could be reduced to as low as 45 sec with little variation in performance. The four major parameters that influence the films prepared by close spaced sublimation, namely substrate temperature, source temperature, ambient pressure, and spacing were optimized for best device performance. The influence of each parameter on deposition rate and cell efficiency was also studied. The best cells produced by this technology had an efficiency of 13% with Voc=830 mV, FF= 74% and Jsc=21.1 mA/cm2.

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