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NOVEL AND NANO-STRUCTURED MATERIALS FOR ADVANCED CHALCOGENIDE PHOTOVOLTAICS

Pokhrel, Dipendra
http://orcid.org/0000-0002-7698-1795
http://rave.ohiolink.edu/etdc/view?acc_num=toledo1670024359945366

Abstract Details

2022, Doctor of Philosophy, University of Toledo, Physics.
Solar energy is a powerful and essential source of renewable energy that works on the principle of the photovoltaic (PV) effect. Among all photovoltaic cell technologies, silicon (Si) dominates with a market share of ~ 90% of the PV industry. Though Si is highly efficient, cadmium telluride (CdTe) competes very effectively with crystalline Si (c-Si) for utility-scale PV and offers advantages in terms of energy payback time (EPBT) and low water impacts. Antimony sulfide (Sb2S3) absorber is an exploratory absorber material with favorable properties like earth abundance, a tunable band gap, and a high absorption coefficient. It also has the potential to serve as a top cell absorber for tandem PV technologies. CdTe is an II-VI semiconductor material with a direct band gap of 1.45 eV. Single junction polycrystalline CdTe solar cells have reached a certified photoconversion efficiency (PCE) of 22.1%. According to the Shockley-Queisser limit, for a material having a band gap of 1.45 eV, the theoretically attainable efficiency is 33.1%, suggesting ample room to improve the CdTe device's efficiency. The low PCE in CdTe is primarily due to the device's low open circuit voltage (VOC) and fill factor (FF). CdTe has a deep valance band edge of 5.9 eV below the vacuum level, that creates a barrier at the back interface, limiting hole transport and reduces the device's performance. The suitable implementation of a back buffer layer between the CdTe absorber and the back electrode is vital in improving monofacial and bifacial CdTe device performance. This dissertation addresses the synthesis and characterization of tellurium (Te) and lead telluride (PbTe) nanowires (NWs), copper iodide (CuI) nanoparticles, copper chromium oxide (CuxCryOz), and their applications to fabricate monofacial and bifacial solar cells based on CdTe as well as CdSexTe1-x absorber layers. In addition, the dissertation presents the fabrication and characterization of Sb2S3 solar cells. Tellurium and lead telluride NWs were synthesized using the hot injection colloidal method, and subsequent experiments successfully demonstrated their suitability as a back buffer layer to CdTe solar cells. The NWs are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Raman Spectroscopy. The NWs show narrow distributions for length, diameter, and aspect ratio. Steady-state photoluminescence (PL) and time-resolved photoluminescence (TRPL) measurements showed improved PL intensity and longer minority carrier lifetime for devices utilizing a PbTe NW back buffer, consistent with surface passivation. Implementing both Te and PbTe NWs as a back buffer layer on CdTe increases the VOC and FF of the devices and enhances the PCE over the control device compared to a straight CuCl2/Au back contact. Copper iodide (CuI) nanoparticles (NPs) were synthesized at room temperature using the solution process method and studied as a potential hole transport layer (HTL) for the fabrication of monofacial and bifacial CdTe solar cells. The device completed with an indium tin oxide (ITO) back electrode (CuI/ITO) has a back-illuminated PCE of 5.5% with a current collection of 12.0 mA cm-2 illuminated from the back. In contrast, devices made only of ITO have a PCE of 1.0%. The enhancement in device performance is due to reduced back barrier height and improved back interface as determined by temperature-dependent J-V and impedance spectroscopy analysis. Similarly, copper chromium oxide (CuxCryOz) is used as a back buffer material for fabricating monofacial and bifacial CdTe solar cells. The high bandgap energy and high transparency in the visible region of CuxCryOz are the keys to serving as a potential back buffer layer on CdTe. The improved carrier lifetime observed with a CuxCryOz back buffer increases the short-circuit current density to 15.8 mA cm-2 and enhances the PCE to 7.6% under the back illumination. The rise in minority carrier lifetime at both the front and back sides of the device is attributed to the reduction of interface recombination due to the reduction of interface recombination velocity. The successful demonstration of CuxCryOz as a back contact interfacial layer to CdTe is a significant step to realizing bifacial thin-film solar cells. I also explored the fabrication of an emerging Sb2S3 thin-film photovoltaic absorber utilizing the hydrothermal deposition method and characterized the deposited thin films using SEM, XRD, Raman spectroscopy, and UV-Vis-NIR spectroscopy. Completed devices based on chemical bath deposited cadmium sulfide (CdS) and spin coating Spiro-OMeTAD as the electron- and hole-transport layers, respectively, have yielded good power conversion efficiencies as high as 5.5 % with VOC values approaching 800 mV. Antimony sulfide has the potential application as a top cell for high-efficiency tandem devices.
Randy J Ellingson (Committee Chair)
Yanfa Yan (Committee Member)
Nikolas J Podraza (Committee Member)
Anne Medling (Committee Member)
Xavier Mathew (Committee Member)
160 p.
Materials Science; Physics
Solar cell, Cadmium telluride, Back contact, Bifacial, Nanoparticles, Antimony Sulfide

Recommended Citations

Citations

  • Pokhrel, D. (2022). NOVEL AND NANO-STRUCTURED MATERIALS FOR ADVANCED CHALCOGENIDE PHOTOVOLTAICS [Doctoral dissertation, University of Toledo]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1670024359945366

    APA Style (7th edition)

  • Pokhrel, Dipendra. NOVEL AND NANO-STRUCTURED MATERIALS FOR ADVANCED CHALCOGENIDE PHOTOVOLTAICS. 2022. University of Toledo, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=toledo1670024359945366.

    MLA Style (8th edition)

  • Pokhrel, Dipendra. "NOVEL AND NANO-STRUCTURED MATERIALS FOR ADVANCED CHALCOGENIDE PHOTOVOLTAICS." Doctoral dissertation, University of Toledo, 2022. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1670024359945366

    Chicago Manual of Style (17th edition)

toledo1670024359945366
72
© 2022, some rights reserved.Creative Commons License NOVEL AND NANO-STRUCTURED MATERIALS FOR ADVANCED CHALCOGENIDE PHOTOVOLTAICS by Dipendra Pokhrel is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. Based on a work at etd.ohiolink.edu.
This open access ETD is published by University of Toledo and OhioLINK.