Characterization of silicon photovoltaic wafers using polarized infrared imaging

Lin, Tung-Wei

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https://hdl.handle.net/2142/89175 Copy

Description

Title

Characterization of silicon photovoltaic wafers using polarized infrared imaging

Author(s)

Lin, Tung-Wei

Issue Date

2015-09-22

Director of Research (if dissertation) or Advisor (if thesis)

Johnson, Harley T

Doctoral Committee Chair(s)

Johnson, Harley T

Committee Member(s)

• Horn, Gavin P
• Beaudoin, Armand
• Ertekin, Elif

Department of Study

Mechanical Sci & Engineering

Discipline

Mechanical Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• photovoltaic
• photoluminescence
• photoelasticity
• dislocation
• silicon

Abstract

Photovoltaic (PV) solar industry uses low-cost material processing methods to produce silicon wafer-based solar cells. Thermal process can introduce crystal defects and residual stress in a PV wafer, which can impact the electrical performance and mechanical reliability of a finished solar cell. This research presents characterization methods for mono-crystal and multi-crystal silicon PV wafers, using an integrated polarized infrared imaging tool capable of both photoelastic (PE) and polarized photoluminescence (PL) imaging. Infrared PE imaging is used to investigate the thermal process-induced residual stress and defect-related stress in mono-crystal silicon PV wafers. The measured stress pattern shows that dislocation structures interact with the thermal residual stress, forming slip band structures oriented at 45 degrees to the wafer edges. The measured PE images are then interpreted using a discrete dislocation-based numerical modeling approach that accounts for stress relaxation in the wafer due to the dislocation structures. The model leads to simulated PE images and is used to analyze the preferred dislocation slip band orientations for wafer strain energy reduction. The analysis is consistent with experimental observations, forming the basis for a more quantitative infrared PE-based inspection method. Crystal growth process for multi-crystal silicon PV wafers results in grain boundaries and dislocation structures that impact solar cell performance. These defects are investigated using the polarized PL imaging setup, which can spatially resolve the defect structures from both the band-to-band and defect-related PL emission. The polarization resolving ability allows the identification and the correlation among different defect types. The technology described here creates a pathway to rapid full-field wafer quality inspection in a manufacturing setting, and will help to improve PV wafer material processing.

Graduation Semester

2015-12

Type of Resource

text

Permalink

http://hdl.handle.net/2142/89175

Copyright and License Information

Copyright 2015 Tung-Wei Lin

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