Date of Award

Summer 8-2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Electrical & Computer Engineering

Program/Concentration

Electrical Engineering

Committee Director

Sylvain Marsillac

Committee Member

Gon Namkoong

Committee Member

Orlando Ayala

Committee Member

Linda Vahala

Abstract

The advancement of low-cost, highly efficient solar cell devices is a major technological challenge demanding suitable materials and fabrication processes. Polycrystalline Cu(In,Ga)Se2 (CIGS) appear to be one of the most promising semiconductor in thin film photovoltaic technology due to its bandgap tunability, high absorption coefficient, and tendency to produce high efficiency solar cells. High-quality CIGS materials fabricated via a three-stage co-evaporation process can convert primary materials into devices with power conversion efficiency above 23%. Increasing the deposition rate and decreasing the deposition temperature, while maintaining high efficiency, is the major concern for the CIGS solar cells to compete with silicon-based technology and to allow their application in industrial domain. A post-deposition treatment of the as-deposited films by alkali halides and selenium improve the devices to some extent. To further accelerate the microstructure evolution, the recrystallization of CIGS thin films via metal halides vapor treatment as a fluxing agent was proposed, as one of the possibilities of producing high-quality CIGS thin films. It is of great interest to recrystallize CIGS, potentially decreasing the fabrication cost and improving the economic viability. In this thesis, different metal halides such as indium bromide, indium chloride, copper chloride and silver bromide were used, with and without supplemental selenium. These compounds promote grain growth, resulting in much larger grains and change the crystallographic structure at low temperature deposition. A significant variation in the sodium profile, and gallium depletion were observed in some halide treatments, whereas no changes in composition profile occurred in others. In terms of devices, indium bromide and indium chloride ex-situ treatment did not yield better devices due to lack of optimal composition profile, but showed drastic changes in morphology evolution, whereas copper chloride and silver bromide in situ recrystallization seemed to be better in terms of device performance, yielding high efficiency devices particularly in case of silver bromide in-situ vapor treatment..

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DOI

10.25777/bm73-9k36

ISBN

9798351481432

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