Chemical and Biological Engineering ETDs

Publication Date

Fall 11-25-2016

Abstract

Space vehicles today are primarily powered by multi-junction photovoltaic cells due to their high efficiency and high radiation hardness in the space environment. While multi-junction solar cells provide high efficiency, microcracks develop in the crystalline semiconductor due to a variety of reasons, including: growth defects, film stress due to lattice constant mismatch, and external mechanical stresses introduced during shipping, installation, and operation. These microcracks have the tendency to propagate through the different layers of the semiconductor reaching the metal gridlines of the cell, resulting in electrically isolated areas from the busbar region, ultimately lowering the power output of the cell and potentially reducing the lifetime of the space mission. Pre-launch inspection are often expensive and difficult to perform, in which individual cells and entire modules must be replaced. In many cases, such microcracks are difficult to examine even with a thorough inspection. While repairs are possible pre-launch of the space vehicle, and even to some extent in low-to-earth missions, they are virtually impossible for deep space missions, therefore, efforts to mitigate the effects of these microcracks have substantial impact on the cell performance and overall success of the space mission. In this effort, we have investigated the use of multi-walled carbon nanotubes as mechanical reinforcement to the metal gridlines capable of bridging gaps generated in the underlying semiconductor while providing a redundant electrical conduction pathway. The carbon nanotubes are embedded in a silver matrix to create a metal matrix composite, which are later integrated onto commercial triple-junction solar cells.

Keywords

Carbon Nanotubes, Composites, Metalization, Photovoltaic Cells, Reliability, Durability

Sponsors

Air Force Research Laboratory

Document Type

Dissertation

Language

English

Degree Name

Chemical Engineering

Level of Degree

Doctoral

Department Name

Chemical and Biological Engineering

First Committee Member (Chair)

Sang M. Han

Second Committee Member

Ganesh Balakrishnan

Third Committee Member

Sang Eon Han

Fourth Committee Member

David M. Wilt

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