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Title:Physical and optoelectronic properties of copper silver indium diselenide thin films
Author(s):Aquino Gonzalez, Angel
Director of Research:Rockett, Angus A.
Doctoral Committee Chair(s):Rockett, Angus A.
Doctoral Committee Member(s):Abelson, John R.; Bishop, Stephen G.; Martin, Lane W.
Department / Program:Materials Science & Engineerng
Discipline:Materials Science & Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
AgInSe2 (AIS)
CuInSe2 (CIS)
Copper indium gallium selenide (CIGS)
solar cells
solar cell
thin film
thin films
copper indium diselenide
silver indium diselenide
copper silver indium diselenide
Abstract:Increasing global energy consumption together with environmental concerns has led to much interest in alternative, cleaner sources of energy such as solar photovoltaic. Researchers in the solar cell community have been looking for ways to reduce costs while maintaining or increasing already high efficiencies. A fundamental understanding of the materials under consideration is essential to rapid development of new technologies. The I-III-VI2 thin film alloys offer promising systems for achieving high efficiency solar cells at lower costs. In fact, by tailoring the chemistry of the compounds it is possible to change the bandgap of the material in order to collect sunlight more efficiently. A promising alloy for tunable bandgap solar cells is the (Cu,Ag)(In,Ga)Se2 system. The focus of my dissertation is to perform a comprehensive characterization of the structural and optoelectronic properties of CuxAg1-xInSe2 alloy thin films in order to gain a better understanding of the material. Detailed physical characterization was carried out in order to reveal differences in the structural properties of the alloy as a function of the Cu/(Cu+Ag) ratio. The identification and behavior of defect levels in the alloy was studied as a function of composition. From this, a band diagram schematic of the defect levels in the films is proposed, which could serve as a blueprint for improvements of the films properties through defect engineering. The effects of alloying Ag with CuInSe2 on the physical properties were shown. The addition of Ag appears to improve the structural quality of the films. This was seen by a reduction in the full-width-at-half-maximum of the luminescence peaks, a reduction in the number of optical transitions, and the appearance of free-to-bound transitions for Ag-dominant films. An increase in the minority carrier lifetime of films with the addition of Ag also supports this conclusion. Furthermore, AgInSe2 films showed less spatial and spectral variations than Cu-containing films in cathodoluminescence measurements, indicating less heterogeneity in the material. The results presented in this dissertation suggest that the CuxAg1-xInSe2 alloy is a suitable candidate for narrow bandgap solar cells. In spite of the observed beneficial effects of Ag, various challenges have been identified through this work. These include the existence of an ordered defect compound near the films surface for compositions of x ≤ 0.2, the predilection of obtaining n-type films for AgInSe2, and the presence of a continuum of defects into the bandgap of Ag-dominant films.
Issue Date:2012-05-22
Rights Information:Copyright 2012 Angel Aquino Gonzalez
Date Available in IDEALS:2012-05-22
Date Deposited:2012-05

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