III-V Metamorphic Materials and Devices for Multijunction Solar Cells Grown via MBE and MOCVD
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| Language: | English |
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The Ohio State University / OhioLINK
2018
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| Online Access: | http://rave.ohiolink.edu/etdc/view?acc_num=osu1534707692114982 |
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ndltd-OhioLink-oai-etd.ohiolink.edu-osu1534707692114982 |
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English |
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Electrical Engineering photovoltaic solar cell multijunction solar cell tunnel junction III-V semiconductor epitaxy metamorphic epitaxy molecular beam epitaxy metal-organic chemical vapor deposition GaAsP AlGaAsP GaInP AlGaInP wide bandgap |
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Electrical Engineering photovoltaic solar cell multijunction solar cell tunnel junction III-V semiconductor epitaxy metamorphic epitaxy molecular beam epitaxy metal-organic chemical vapor deposition GaAsP AlGaAsP GaInP AlGaInP wide bandgap Chmielewski, Daniel Joseph III-V Metamorphic Materials and Devices for Multijunction Solar Cells Grown via MBE and MOCVD |
| author |
Chmielewski, Daniel Joseph |
| author_facet |
Chmielewski, Daniel Joseph |
| author_sort |
Chmielewski, Daniel Joseph |
| title |
III-V Metamorphic Materials and Devices for Multijunction Solar Cells Grown via MBE and MOCVD |
| title_short |
III-V Metamorphic Materials and Devices for Multijunction Solar Cells Grown via MBE and MOCVD |
| title_full |
III-V Metamorphic Materials and Devices for Multijunction Solar Cells Grown via MBE and MOCVD |
| title_fullStr |
III-V Metamorphic Materials and Devices for Multijunction Solar Cells Grown via MBE and MOCVD |
| title_full_unstemmed |
III-V Metamorphic Materials and Devices for Multijunction Solar Cells Grown via MBE and MOCVD |
| title_sort |
iii-v metamorphic materials and devices for multijunction solar cells grown via mbe and mocvd |
| publisher |
The Ohio State University / OhioLINK |
| publishDate |
2018 |
| url |
http://rave.ohiolink.edu/etdc/view?acc_num=osu1534707692114982 |
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AT chmielewskidanieljoseph iiivmetamorphicmaterialsanddevicesformultijunctionsolarcellsgrownviambeandmocvd |
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ndltd-OhioLink-oai-etd.ohiolink.edu-osu15347076921149822021-08-03T07:08:18Z III-V Metamorphic Materials and Devices for Multijunction Solar Cells Grown via MBE and MOCVD Chmielewski, Daniel Joseph Electrical Engineering photovoltaic solar cell multijunction solar cell tunnel junction III-V semiconductor epitaxy metamorphic epitaxy molecular beam epitaxy metal-organic chemical vapor deposition GaAsP AlGaAsP GaInP AlGaInP wide bandgap III-V multijunction solar cells (MJSC) are capable of the highest conversion efficiencies among all solar cell classifications. These devices are thus of major interest for both terrestrial and space applications. However, the economics of the terrestrial and space markets leads to significantly different design requirements for III-V MJSCs to become more economically viable in each market.In the terrestrial market, despite their high efficiency, the high manufacturing cost of III-V MJSCs currently limits their applicability in a market that is currently dominated by crystalline silicon. Thus, lower cost III-V MJSC approaches must be developed for them to become more competitive. This intuitively leads to the concept of merging III-V MJSCs with Si solar cells to demonstrate III-V/Si MJSCs. Such an approach simultaneously takes advantage of the high conversion efficiency of III-V MJSCs and the low-cost manufacturing of Si.In the space market, III-V MJSCs are already the dominant technology due to their high efficiency, radiation hardness, and reliability in extreme conditions. However, new III-V MJSC approaches must be developed if they are to push the boundary of conversion efficiency even further. An approach to improve the efficiency and thus economic viability is through the use of additional high-performance sub-cells at optimal bandgaps to more ideally partition the solar spectrum.Although the design requirements for improving the economic viability of III-V MJSCs in the terrestrial and space markets differ drastically, the design of III-V MJSCs can be altered to meet the design requirements for both markets by using the versatile technique of III-V metamorphic epitaxy. This is the growth of relaxed (i.e. unstrained) III-V compounds at a lattice constant that differs from that of the substrate. The major advantage of III-V metamorphic epitaxy is that it provides an additional degree of freedom for III-V MJSC device design. Traditional lattice-matched growth limits the number of materials that are available to integrate with the substrate material, which in turn limits the available bandgaps that can be achieved for a given III-V MJSC design.This dissertation aims to leverage III-V metamorphic epitaxy to develop various critical components of III-V MJSCs grown by both molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD). This includes the development of metamorphic tunnel junctions to enable III-V/Si MJSC approaches for future terrestrial applications and the development of wide bandgap (Al<sub>z</sub>Ga<sub>1-z</sub>)<sub>x</sub>In<sub>1-x</sub>P top cells (lattice-matched vs. metamorphic) to push the efficiency limits of III-V MJSC approaches for future space applications.Tunnel junctions serve as low-resistance, optically transparent interconnects between adjacent sub-cells within MJSCs. For III-V/Si MJSCs, these tunnel junctions are ideally grown at the same lattice constant as the metamorphic III-V sub-cells. Therefore, metamorphic tunnel junctions with relatively unexplored lattice constants are necessary. Development of these metamorphic tunnel junctions initially began with MBE-grown materials and devices. At this early stage of research, the III-V/Si MJSC approach primarily focused on the MBE grown triple-junction solar cell designed for operation under high concentration. This in turn specified a variety of requirements for the necessary lower and upper tunnel junctions of the triple-junction including the necessary peak tunneling current (<i>J</i><sub>P</sub>), resistance-area product (<i>RA</i>), and bandgap to minimize parasitic losses within the tunnel junction.After initial development of an MBE grown metamorphic GaAs<sub>0.9</sub>P<sub>0.1</sub> homojunction tunnel junction, efforts culminated in the demonstration of a high-performance metamorphic double heterostructure tunnel junction. This device achieved <i>J</i><sub>P</sub> = 510 A·cm <sup>2</sup> and <i>RA</i> = 2.0×10 <sup>4</sup> ohm·cm<sup>2</sup>; due to these excellent electronic properties, as well as its high optical transparency, this device is suitable for both the lower and upper tunnel junction in the triple-junction. Upon integration into a Ga<sub>0.57</sub>In<sub>0.43</sub>P/GaAs<sub>0.9</sub>P<sub>0.1</sub> dual-junction solar cell (a subset of the triple-junction containing only the III-V sub-cells and upper tunnel junction) the tunnel junction operated successfully. Thus, such a design is very promising for future III-V/Si triple-junction solar cells.III-V metamorphic epitaxy was used to explore new III-V MJSC approaches for future space applications. Current research trends are pushing to increase the efficiency of III-V MJSCs via the use of more sub-cells compared to the traditional triple-junction solar cell design. As the number of sub-cell increase from 4 to 6, the ideal bandgap profile of the MJSC shifts the bandgap of the top cell from ~2.05 eV to ~2.3 eV, respectively. Although the ideal bandgap required for the top cell can be achieved via lattice-matched (Al<sub>z</sub>Ga<sub>1-z</sub>)<sub>0.52</sub>In<sub>0.48</sub>P, the necessary Al content tends to reduce device performance due to increased oxygen content. Thus, an alternative solution was explored for achieving a 2.05 eV top cell via the use of III-V metamorphic epitaxy.Al content versus misfit was compared in MOCVD-grown lattice-matched (Al<sub>0.32</sub>Ga<sub>0.68</sub>)<sub>0.52</sub>In<sub>0.48</sub>P and metamorphic Ga<sub>0.66</sub>In<sub>0.34</sub>P solar cells. Results demonstrated that the metamorphic Ga<sub>0.66</sub>In<sub>0.34</sub>P solar cell possessed substantially higher short wavelength current collection. This was due to the wider-bandgap, internally lattice-matched window layer of the metamorphic Ga<sub>0.66</sub>In<sub>0.34</sub>P cell, as well as a longer emitter diffusion length. Device modeling and characterization results suggested similar base diffusion lengths in each cell, and ultimately merits to both approaches were demonstrated. 2018 English text The Ohio State University / OhioLINK http://rave.ohiolink.edu/etdc/view?acc_num=osu1534707692114982 http://rave.ohiolink.edu/etdc/view?acc_num=osu1534707692114982 unrestricted This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws. |