Dissertations, Theses, and Capstone Projects

Date of Degree

2-2025

Document Type

Dissertation

Degree Name

Ph.D.

Program

Physics

Advisor

Yuhang Ren

Committee Members

Steve Greenbaum

Ying-Chih Chen

Godfrey Gumbs

Yu Zhang

Subject Categories

Condensed Matter Physics | Engineering Physics

Keywords

ACIGS, silver doping, alkali fluoride PDT

Abstract

Our dissertation demonstrates the optimization of ACIGS (Ag-Cu-In-Ga-Se) thin-film solar cells, achieving an efficiency of 20.4% through the combined effects of silver incorporation and alkali metal post-deposition treatment (PDT). The incorporation of 2.8% Ag into the CIGS lattice enhanced crystal quality, reduced disorder, and widened the bandgap by 0.103 eV, as evidenced by a significant reduction in Urbach energy. These improvements resulted in stronger light absorption, increased carrier generation, and enhanced photovoltaic parameters, including a short-circuit current density Jsc of 35.31 mA/cm², an open-circuit voltage Voc of 0.74 V, and a fill factor (FF) of 75.8%. PDT using rubidium fluoride (RbF) and potassium fluoride (KF) further passivated defects at grain boundaries and interfaces, minimized recombination losses, and improved carrier collection, contributing to the observed high efficiency.

Comprehensive characterization techniques in our dissertation provided critical insights into material and device performance. X-ray fluorescence (XRF) and glow discharge optical emission spectroscopy (GDOES) revealed uniform depth profiles for Ag and optimized Ga gradients essential for effective charge transport. Spectroscopy external quantum efficiency(EQE) measurements confirmed sharper band edges and reduced sub-bandgap absorption due to Ag doping, while PDT refined interface quality. These findings underscore the importance of combining silver alloying and PDT to improve the optoelectronic properties of ACIGS, enabling its application in flexible and high-performance photovoltaic technologies.

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