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Title:Characterization of silicon photovoltaic wafers using polarized infrared imaging
Author(s):Lin, Tung-Wei
Director of Research:Johnson, Harley T
Doctoral Committee Chair(s):Johnson, Harley T
Doctoral Committee Member(s):Horn, Gavin P; Beaudoin, Armand; Ertekin, Elif
Department / Program:Mechanical Sci & Engineering
Discipline:Mechanical Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
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.
Issue Date:2015-09-22
Rights Information:Copyright 2015 Tung-Wei Lin
Date Available in IDEALS:2016-03-02
Date Deposited:2015-12

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