Graduation Year

2005

Document Type

Thesis

Degree

M.S.E.E.

Degree Granting Department

Electrical Engineering

Major Professor

Christos S. Ferekides, Ph.D.

Committee Member

Don Morel, Ph.D.

Committee Member

Yun L. Chiou, Ph.D.

Keywords

Photovoltaics, Sputtering, Sublimation, Thin films, Stability

Abstract

CdTe is one of the most promising absorbers for use in inexpensive semiconductor solar cells having achieved a high efficiency of 16.4% in small area cells [1]. One of the most important technological problems in obtaining high efficiencies is to have a good ohmic contact on the CdTe, which is characterized by a very high work function [2]. Cu is used as a dopant in CdTe at the contact to promote quantum mechanical tunneling [3]. But the oversupply of Cu causes the diffusion of Cu through CdTe to the underlying CdS layer resulting in the degradation of the cell performance. It has been reported that Cu was segregated near the CdS/CdTe junction. To avoid the Cu segregation at the junction, Cu supply should be minimized while the ohmic characteristics of p-CdTe contact are maintained [4].

In this thesis, the main objective is to understand the role of Cu at the CdS/CdTe interface. Here the Cu is added at the CdS/CdTe interface and is avoided at the back contact. It is been reported that metals like Mo does not diffuse into the cell. In this thesis, Mo is deposited as the back contact metal. The deposition conditions are varied to find the optimum device performance. The Cu concentration is also varied to study the role of Cu at the interface and the cells are compared with the conventional solar cells where Cu is used at the back contact.

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