Date of Award

Spring 2019

Document Type

Open Access Dissertation

Department

Electrical Engineering

First Advisor

Krishna C. Mandal

Abstract

The dissertation study has undertaken research in two areas: (1) development of Cu2ZnSnS4 (CZTS) thin film photo-absorber using low-cost fabrication technique for roll- to-roll commercial production for photovoltaic application, and (2) development of enriched lithium-doped amorphous selenium alloy film, a new solid-state detector material for neutron detection.

In this study CZTS thin film was developed by employing low-cost, high- throughput spray pyrolysis technique, followed by sulfurization under a 5% H2S flow at 550°C. Characterization of deposited films revealed better structural, compositional, and optical properties for sulfurized film compared to as-deposited film. The ‘sulfurized’ CZTS films deposited at 380°C substrate temperature were used for fabrication of CZTS/CdS heterojunction solar cells. The champion cell exhibited an open-circuit voltage (VOC) of 509 mV, a short-circuit current density (Jsc) of 11.8 mA/cm2, and a fill factor 0.362, resulting in a total area efficiency of 2.17% under AM 1.5G illumination measured at 297K. Further investigation revealed that presence of both low shunt resistance and high series resistance degraded fill factor and consequently efficiency of the solar cell.

Feasibility of a new thermal neutron detector based on lithium-doped a-Se (As, Cl) semiconductor film was investigated. Monodispersed alloy materials with up to 28 a/o lithium doping concentration were synthesized. Alloy films up to an area of 1010 cm2 with a thickness of ~500 m were fabricated. Physical and optical properties such as crystalline structure, melting point, crystallization temperature, stoichiometry, energy bandgap were determined for the grown alloy using a series of characterization techniques. Current-voltage (I-V) characteristics showed ~1012 Ω-cm resistivity with very low leakage current (~1 nA at ~1000V). Device with Al/Al2O3 layer as an electron-blocking layer and/or Sb2S3 as a hole-blocking layer further reduced the leakage current of the device and improved performance by controlling carrier transport. Nuclear testing with high-energy alpha (241Am) and neutron (252Cf) sources showed specific signature of thermal neutrons for the first time with enriched Li-doped a-Se alloy.

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