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Transition Metal Dichalcogenides for Next-Generation Photovoltaics.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Transition Metal Dichalcogenides for Next-Generation Photovoltaics./
作者:	Nazif, Koosha Nassiri.
出版者:	Ann Arbor : ProQuest Dissertations & Theses, : 2021,
面頁冊數:	102 p.
附註:	Source: Dissertations Abstracts International, Volume: 83-09, Section: B.
Contained By:	Dissertations Abstracts International83-09B.
標題:	Silicon. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=29003864
ISBN:	9798209784746

Transition Metal Dichalcogenides for Next-Generation Photovoltaics.
Nazif, Koosha Nassiri.

Transition Metal Dichalcogenides for Next-Generation Photovoltaics. - Ann Arbor : ProQuest Dissertations & Theses, 2021 - 102 p.

Source: Dissertations Abstracts International, Volume: 83-09, Section: B.

Thesis (Ph.D.)--Stanford University, 2021.

This item must not be sold to any third party vendors.

Conventional silicon solar cells dominate the photovoltaics market with a market share of about 95% due to their low-cost manufacturing and reasonable power conversion efficiency. However, the low optical absorption coefficient and brittle nature of silicon lead to degraded performance in ultrathin, flexible silicon solar cells and therefore prevent their broader usage in next-generation photovoltaic applications demanding high specific power (power per weight) and flexibility, for example in aerospace, transportation, architecture and self-powered wearable and implantable electronics. In addition, for widespread adoption of solar energy, new materials need to be integrated on silicon to form tandem solar cells with higher efficiency, lower cost per Watt and therefore higher affordability.Semiconducting transition metal dichalcogenides (TMDs) are promising for flexible high-specific-power photovoltaics and for silicon-based tandem solar cells, due to their ultrahigh optical absorption coefficients, desirable band gaps, self-passivated surfaces, high stability and lifetime, biocompatibility, eco-friendliness, and compatibility with existing nanoelectronic fabrication processes. However, challenges such as Fermi-level pinning at the metal contact-TMD interface and the inapplicability of traditional doping schemes have prevented most TMD solar cells from exceeding 2% power conversion efficiency. In addition, fabrication on flexible substrates tends to contaminate or damage TMD interfaces, further reducing performance.In this work, we investigate the promise and challenges of TMDs as next-generation photovoltaic materials and provide novel and scalable solutions for their challenges, leading to record high performance on par with prevailing thin-film solar technologies.First, we perform realistic detailed balance calculations for various single-junction TMD solar cells as well as TMD-silicon tandem solar cells. These calculations provide close approximation of the maximum PCE attainable in practice upon optimization of optical and electronic designs. The results reveal that ultrathin (~100 nm) single-junction TMD solar cells can realistically achieve ~27% PCE even at moderate material quality corresponding to carrier lifetimes as short as 100 ns. Similarly, we show that PCEs of 30% and higher can be practically achieved in TMD-silicon tandem solar cells. v Next, we introduce MoOx (x ≈ 3) capping as an effective and scalable method to p-dope TMDs and passivate their surface defects, leading to record open circuit voltage of 681 mV, highest among all p-n junction TMD solar cells. The enhanced VOC also leads to record PCE of 1.55% in ultrathin (<90 nm) WS2 photovoltaics. Doping and passivation effects of MoOx are confirmed and quantified by various electrical characterization techniques. High hole doping densities of up to 1013 cm-2 are measured. Thicknessdependent performance of the devices are explained by optical simulation. External and internal quantum efficiencies are also measured to characterize the absorption and charge carrier collection processes in the devices.Finally, we present the first-ever high-specific-power flexible TMD solar cells realized by integrating various novel solutions including 1) transparent graphene contacts to mitigate Fermi-level pinning, 2) MoOx capping for doping, passivation and antireflection, and 3) a clean, non-damaging direct transfer method to make devices on lightweight flexible polyimide substrates. These lead to record PCE of 5.1% and record specific power of 4.4 W g-1 for flexible TMD (WSe2) solar cells, the latter on par with prevailing thin-film solar technologies cadmium telluride, copper indium gallium selenide, amorphous silicon and III-Vs. We perform material, electrical, and optical characterization and simulation, including Raman spectroscopy, I-V measurement under different illumination conditions, spectral absorption measurement/simulation and photocurrent mapping, to explain the superior performance of the devices. We also confirm consistent photovoltaic performance under tensile bending at curvature radius of 4 mm. Ultimately, we project that future TMD solar cells on even thinner substrates and with higher PCEs could potentially achieve an additional 10x increase in specific power, creating game-changing opportunities in a broad range of industries, from aerospace to wearable and implantable electronics.

ISBN: 9798209784746Subjects--Topical Terms:

669429
Silicon.

Transition Metal Dichalcogenides for Next-Generation Photovoltaics.
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300 $a 102 p.
500 $a Source: Dissertations Abstracts International, Volume: 83-09, Section: B.
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502 $a Thesis (Ph.D.)--Stanford University, 2021.
506 $a This item must not be sold to any third party vendors.
520 $a Conventional silicon solar cells dominate the photovoltaics market with a market share of about 95% due to their low-cost manufacturing and reasonable power conversion efficiency. However, the low optical absorption coefficient and brittle nature of silicon lead to degraded performance in ultrathin, flexible silicon solar cells and therefore prevent their broader usage in next-generation photovoltaic applications demanding high specific power (power per weight) and flexibility, for example in aerospace, transportation, architecture and self-powered wearable and implantable electronics. In addition, for widespread adoption of solar energy, new materials need to be integrated on silicon to form tandem solar cells with higher efficiency, lower cost per Watt and therefore higher affordability.Semiconducting transition metal dichalcogenides (TMDs) are promising for flexible high-specific-power photovoltaics and for silicon-based tandem solar cells, due to their ultrahigh optical absorption coefficients, desirable band gaps, self-passivated surfaces, high stability and lifetime, biocompatibility, eco-friendliness, and compatibility with existing nanoelectronic fabrication processes. However, challenges such as Fermi-level pinning at the metal contact-TMD interface and the inapplicability of traditional doping schemes have prevented most TMD solar cells from exceeding 2% power conversion efficiency. In addition, fabrication on flexible substrates tends to contaminate or damage TMD interfaces, further reducing performance.In this work, we investigate the promise and challenges of TMDs as next-generation photovoltaic materials and provide novel and scalable solutions for their challenges, leading to record high performance on par with prevailing thin-film solar technologies.First, we perform realistic detailed balance calculations for various single-junction TMD solar cells as well as TMD-silicon tandem solar cells. These calculations provide close approximation of the maximum PCE attainable in practice upon optimization of optical and electronic designs. The results reveal that ultrathin (~100 nm) single-junction TMD solar cells can realistically achieve ~27% PCE even at moderate material quality corresponding to carrier lifetimes as short as 100 ns. Similarly, we show that PCEs of 30% and higher can be practically achieved in TMD-silicon tandem solar cells. v Next, we introduce MoOx (x ≈ 3) capping as an effective and scalable method to p-dope TMDs and passivate their surface defects, leading to record open circuit voltage of 681 mV, highest among all p-n junction TMD solar cells. The enhanced VOC also leads to record PCE of 1.55% in ultrathin (<90 nm) WS2 photovoltaics. Doping and passivation effects of MoOx are confirmed and quantified by various electrical characterization techniques. High hole doping densities of up to 1013 cm-2 are measured. Thicknessdependent performance of the devices are explained by optical simulation. External and internal quantum efficiencies are also measured to characterize the absorption and charge carrier collection processes in the devices.Finally, we present the first-ever high-specific-power flexible TMD solar cells realized by integrating various novel solutions including 1) transparent graphene contacts to mitigate Fermi-level pinning, 2) MoOx capping for doping, passivation and antireflection, and 3) a clean, non-damaging direct transfer method to make devices on lightweight flexible polyimide substrates. These lead to record PCE of 5.1% and record specific power of 4.4 W g-1 for flexible TMD (WSe2) solar cells, the latter on par with prevailing thin-film solar technologies cadmium telluride, copper indium gallium selenide, amorphous silicon and III-Vs. We perform material, electrical, and optical characterization and simulation, including Raman spectroscopy, I-V measurement under different illumination conditions, spectral absorption measurement/simulation and photocurrent mapping, to explain the superior performance of the devices. We also confirm consistent photovoltaic performance under tensile bending at curvature radius of 4 mm. Ultimately, we project that future TMD solar cells on even thinner substrates and with higher PCEs could potentially achieve an additional 10x increase in specific power, creating game-changing opportunities in a broad range of industries, from aerospace to wearable and implantable electronics.
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