Graduation Year

2005

Document Type

Thesis

Degree

M.S.E.E.

Degree Granting Department

Electrical Engineering

Major Professor

Christos S. Ferekides, Ph.D.

Co-Major Professor

Don L. Morel, Ph.D.

Committee Member

Yun L. Chiou, Ph.D.

Keywords

TCO, Photovoltaic, Resistive Layer, Processing, ZTO

Abstract

CdS/CdTe solar cell performance and reproducibility can be improved by integrating a ZTO buffer layer, which interdiffuses into the CdS layer during device fabrication. Reducing the thickness of CdS layer improves the QE in the blue spectral region without affecting the device performance. This buffer layer is expected to prevent the formation of localized TCO/CdTe junction during high temperature processing.

The CdS/CdTe Solar Cell was modified by introducing ZTO as a buffer layer between the window layer (CdS) and the absorber layer (CdTe). Studies were performed on different varying ZTO processing parameters like (a) Zn/Sn atomic ratios during sputtering process, (b) ZTO thickness, (c) ZTO heat treatment temperature, and (d) ZTO heat treatment ambient. Devices were also fabricated to study the effects of (1) window layer thickness, (2) CdTe substrate temperature, and (3) post heat treatment of CdCl2.

Using Zinc Stannate as a buffer layer (SnO2: F/ZTO/CdS/CdTe) resulted in Voc of 830mV, 71.2% FF and Jsc of 22.58mA/cm 2 with total efficiency of 13.34%. The best device had a 500Å thick Zinc Stannate film deposited at 400oC in Ar ambient and annealed in He ambient for 20 minutes at 600oC. High sheet resistance of Zinc Stannate makes it suitable as a buffer layer. It has more than 90% transmission in the visible region. As-deposited ZTO at RT is amorphous and subsequent heat treatment makes it crystalline

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