Date of Award

10-2-2019

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Applied Science

First Advisor

Tansel Karabacak

Abstract

Flexible photodetectors (PD) with high photoresponse and low-cost fabrication have been an attractive research topic due to their applications. Device construction is the primary key to build a flexible device which can be mechanically durable under strain. One dimensional (1D) nanomaterials, including nanowires (NWs), nanopillars, and nanotubes, are superior building blocks for high-performance flexible photodetectors due to their unique physical and mechanical properties. In contrast with the traditionally rigid and fragile photodetectors, flexible and nanostructured photodetectors can efficiently capture light and collect the electors when integrated on curved surfaces due to their performance and mechanical durability. The main emphasis has been on developing high-performance nanostructures photodetectors with high mechanical flexibility. This dissertation presents the design, fabrication, and test of flexible nanostructured photodetectors constructed with vertically aligned nanorods bonded to a flexible polymeric substrate. In this study, we show a simple way to fabricate high performance core-shell nanostructured flexible photodetectors on a polyimide substrate of Kapton. For this purpose, copper indium gallium selenide (CIGS). Three different designs of nanostructured flexible devices have been prepared by glancing angle deposition (GLAD) technique using an RF/DC magnetron sputtering unit at room temperature. The process is scalable, cost-effective, low temperature, and applicable to any substrate. The results revealed promising performance for these core-shell nanostructured flexible photodetectors, including high photoconductive gain, responsivity, detectivity, and mechanical durability. As a comparison, we also fabricated conventional planar thin film devices incorporating CIGS film of similar material loading to that of CIGS and molybdenum (Mo) nanorod devices. The morphological characterization was carried out by a field-emission scanning electron microscope. The photocurrent measurement conducted under AM 1.5 sun at zero electrical biasing, where CIGS and Mo devices were observed to absorb in the UV-Vis-NIR spectrum. The core-shell flexible photodetectors show significantly higher photocurrent than most of the flexible photodetectors reported in the literature. Moreover, our nanorod devices recovered their photoresponse after several bending experiments that indicate their enhanced mechanical durability. Improved photocurrent of nanorod devices is believed to be due to their enhanced light trapping property and the reduced inter-electrode distance because of the core-shell structure, which allows the efficient capture of the photo-generated carriers.

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