Residual stresses and mechanical properties of thin film photovoltaic materials

The mean and gradient residual stresses and the failure behavior of individual layers in inorganic thin film photovoltaics were investigated. The thin film photovoltaics consisted of an amorphous silicon (Si) p-n junction diode, a zinc oxide (ZnO) Transparent Conductive Oxide (TCO) layer (each 1μm thick), a Kapton® polyimide layer acting as the bottom cathode and a thick aluminum substrate. Analysis of straight blister delaminations in the p-n junction layer and telephone cord type delaminations in the p-n junction-TCO bilayer provided the mean residual stress values in the Si monolayer and the Si/ZnO bilayer, which were -466±118 MPa and -661±93 MPa, respectively. High aspect ratio freestanding strips of the Si/ZnO bilayer and the Si monolayer were used to determine the residual stress gradient using curvature measurements. The stress gradient in the Si monolayer layer was 274±20 MPa/μm while the stress gradient in the Si/ZnO bilayer resulted in a maximum tensile stress value of 360±27 MPa at the top of the ZnO layer and a maximum compressive stress of 319±24 MPa at the bottom surface of the Si layer. The monolayer and bilayer strips were also subjected to uniaxial tension with a microscale tension apparatus to determine the failure strength and the elastic modulus of each layer. The elastic modulus of the amorphous Si monolayer was 94±6 GPa, which is in agreement with bulk values. The bilayer strips, had an elastic modulus of 107±7 GPa which provided a value of 120±13 GPa for the Young’s modulus of the ZnO layer, and tensile strength that was significantly lower than the Si monolayer. These results indicated poor adhesion and load transfer between the amorphous Si and the ZnO film and a mechanically weak ZnO film. Finally, proof of concept experiments were conducted with photovoltaic cells attached to carbon fiber composites, which showed extensive fragmentation of the thin film photovoltaics occurring at small strains without though significant loss of functional performance of the cells until ~3% strain in the composite laminate.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Aerospace Engineering

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2012

Author dc:creator

• Antartis, Dimitrios

Contributors dc:contributor

• Chasiotis, Ioannis

• Thin film solar cells
• mechanical performance

Statement dc:rights

• Copyright 2012 Dimitrios Antartis. Portions Copyright 2005, Nature Materials, Copyright 2010, Solar Energy, Copyright 2002, Physics of Solids.

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/34218

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/34218