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Crystals
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III-V Heteroepitaxy for Solar Energy Conversion
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III-V Heteroepitaxy for Solar Energy Conversion

A special issue of Crystals (ISSN 2073-4352).

Deadline for manuscript submissions: closed (28 February 2019)

Special Issue Editor

Dr. Henning Döscher

E-Mail Website
Guest Editor
Competence Center Emerging Technologies,
Fraunhofer Institute for Systems and Innovation Research ISI,
Breslauer Str. 48 | 76139 Karlsruhe | Germany
Interests: III-V semiconductors; epitaxy; in situ analysis; surface science; critical interfaces; solar energy; photoelectrochemistry; innovation systems; technology roadmapping

Special Issue Information

Dear Colleagues,

III-V devices have set efficiency records, in both photovoltaic and photoelectrochemical conversion of solar energy, for decades. The unrivalled technical merits are based on: (a) superior semiconductor properties; (b) advanced epitaxial material quality; and (c) facile heterostructure integration. The III-V material system dominates optoelectronic technologies—except for solar energy conversion, where the high cost still constrains commercial success in niche markets. Vast promises and critical bottlenecks associated with III-V materials in solar energy generation constitute a challenging context for the current Special Issue.

This Special Issue, on “III-V Heteroepitaxy for Solar Energy Conversion”, is intended to provide a unique international forum, aimed at exploring both technological perspectives and commercialization prospects of epitaxial III-V absorbers, with respect to future sustainable systems. Scientists working in a wide range of disciplines are invited to contribute to this Special Issue.

The keywords below broadly cover the general topics, framing a greater number of sub-topics that we have in mind. This volume, especially, is open to visionary and/or interdisciplinary work addressing advanced epitaxial devices or components for solar energy systems, or prospects for their widespread application. Subject areas of particular interest include:

  • Advanced solar absorber structures and concepts
  • Multi-junction photovoltaics and device implementation strategies
  • Efficient solar fuel generation and material durability
  • Structural characterization and in situ analysis
  • High-volume production and emerging growth techniques
  • Alternative substrates and substrate reuse
  • Sustainability and economic viability

Dr. Henning Döscher
Guest Editor

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Crystals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2100 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • III-V semiconductors
  • Epitaxial growth
  • Photovoltaics
  • Solar fuel generation

 

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Published Papers (3 papers)

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Research

Jump to: Review

9 pages, 1492 KiB  
Article
Optical Characterization and Photovoltaic Performance Evaluation of GaAs p-i-n Solar Cells with Various Metal Grid Spacings
by Jenq-Shinn Wu, Der-Yuh Lin, Yun-Guang Li, Hung-Pin Hsu, Ming-Cheng Kao and Hone-Zern Chen
Crystals 2019, 9(3), 170; https://doi.org/10.3390/cryst9030170 - 22 Mar 2019
Cited by 4 | Viewed by 2987
Abstract
GaAs p-i-n solar cells are studied using electroreflectance (ER) spectroscopy, light beam induced current (LBIC) mapping and photovoltaic characterization. Using ER measurements, the electric field across the pn junction of a wafer can be evaluated, showing 167 kV/cm and 275 kV/cm in the [...] Read more.
GaAs p-i-n solar cells are studied using electroreflectance (ER) spectroscopy, light beam induced current (LBIC) mapping and photovoltaic characterization. Using ER measurements, the electric field across the pn junction of a wafer can be evaluated, showing 167 kV/cm and 275 kV/cm in the built-in condition and at −3 V reverse bias, respectively. In order to understand the effect of the interval between metal grids on the device’s solar performance, we performed LBIC mapping and solar illumination on samples of different grid spacings. We found that the integrated photocurrent intensity of LBIC mapping shows a consistent trend with the solar performance of the devices with various metal grid spacings. For the wafer used in this study, the optimal grid spacing was found to be around 300 μm. Our results clearly show the importance of the metal grid pattern in achieving high-efficiency solar cells. Full article
(This article belongs to the Special Issue III-V Heteroepitaxy for Solar Energy Conversion)
►▼ Show Figures

Figure 1

Figure 1
<p>Electroreflectance spectra under different bias voltages.</p> Full article ">Figure 2
<p>Plot of (4/3π)(<span class="html-italic">E<sub>j</sub></span> − <span class="html-italic">E<sub>g</sub></span>)<sup>3/2</sup> as a function of index <span class="html-italic">j</span> for sample A.</p> Full article ">Figure 3
<p>Light beam induced current (LBIC) mapping images of (<b>a</b>) sample A, (<b>b</b>) sample B, (<b>c</b>) sample C, and (<b>d</b>) sample D.</p> Full article ">Figure 4
<p>LBIC scanning profiles crossing the metal grids for (<b>a</b>) sample A, (<b>b</b>) sample B, (<b>c</b>) sample C, and (<b>d</b>) sample D.</p> Full article ">Figure 5
<p>I-V characteristics of the samples under AM 1.5 solar power.</p> Full article ">Figure 6
<p>Equivalent circuit of solar cell with series resistance <span class="html-italic">R<sub>s</sub></span> and shunt resistance <span class="html-italic">R<sub>sh</sub></span>.</p> Full article ">

Review

Jump to: Research

15 pages, 932 KiB  
Review
Tunnel Junctions for III-V Multijunction Solar Cells Review
by Peter Colter, Brandon Hagar and Salah Bedair
Crystals 2018, 8(12), 445; https://doi.org/10.3390/cryst8120445 - 28 Nov 2018
Cited by 38 | Viewed by 10276
Abstract
Tunnel Junctions, as addressed in this review, are conductive, optically transparent semiconductor layers used to join different semiconductor materials in order to increase overall device efficiency. The first monolithic multi-junction solar cell was grown in 1980 at NCSU and utilized an AlGaAs/AlGaAs tunnel [...] Read more.
Tunnel Junctions, as addressed in this review, are conductive, optically transparent semiconductor layers used to join different semiconductor materials in order to increase overall device efficiency. The first monolithic multi-junction solar cell was grown in 1980 at NCSU and utilized an AlGaAs/AlGaAs tunnel junction. In the last 4 decades both the development and analysis of tunnel junction structures and their application to multi-junction solar cells has resulted in significant performance gains. In this review we will first make note of significant studies of III-V tunnel junction materials and performance, then discuss their incorporation into cells and modeling of their characteristics. A Recent study implicating thermally activated compensation of highly doped semiconductors by native defects rather than dopant diffusion in tunnel junction thermal degradation will be discussed. AlGaAs/InGaP tunnel junctions, showing both high current capability and high transparency (high bandgap), are the current standard for space applications. Of significant note is a variant of this structure containing a quantum well interface showing the best performance to date. This has been studied by several groups and will be discussed at length in order to show a path to future improvements. Full article
(This article belongs to the Special Issue III-V Heteroepitaxy for Solar Energy Conversion)
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Figure 1

Figure 1
<p>I-V characteristics of the tunnel diodes (<b>a</b>) as-grown and (<b>b</b>) annealed at 650 °C for 30 min. (<b>a</b>) was measured at room temperature and at 150° K. (<b>b</b>) was measured at room temperature [<a href="#B16-crystals-08-00445" class="html-bibr">16</a>].</p> Full article ">Figure 2
<p>EQE of inverted triple-junction solar cells that will form the top junctions of a 6J cell. The dashed lines use the old nontransparent TJ that consists of n and p Al<sub>0.3</sub>Gal<sub>0.7</sub>As layers with a 12-nm GaAs QW while the solid lines use a more transparent TJ [<a href="#B37-crystals-08-00445" class="html-bibr">37</a>].</p> Full article ">Figure 3
<p>(<b>a</b>) Junction grown with a 30-Å quantum well at high growth rate. The annealing occurs for 15 min at 625 °C [<a href="#B17-crystals-08-00445" class="html-bibr">17</a>] and (<b>b</b>) Te segregation at surface and its effect on grown structure [<a href="#B19-crystals-08-00445" class="html-bibr">19</a>].</p> Full article ">Figure 4
<p>The J-V characteristics of an InGaP/GaAs (50 Å)/AlGaAs TJ, both as-grown and annealed for 30 min at 650 °C for the low growth rate structure coupled with the early Te source shut-off [<a href="#B19-crystals-08-00445" class="html-bibr">19</a>].</p> Full article ">Figure 5
<p>(<b>a</b>) Example of junction tunneling width and depletion layer width and (<b>b</b>) Peak tunneling current for model 1.91 eV band gap tunneling junction [<a href="#B45-crystals-08-00445" class="html-bibr">45</a>].</p> Full article ">Figure 6
<p>(<b>a</b>) Band diagram for structure incorporating a GaAs quantum well at the junction [<a href="#B18-crystals-08-00445" class="html-bibr">18</a>] and (<b>b</b>) Peak tunneling current range for various In<sub><span class="html-italic">x</span></sub>Ga<sub>1−<span class="html-italic">x</span></sub>P:Te/GaAs:Te/Al<sub>0.6</sub>Ga<sub>0.4</sub>As:C tunnel junction architectures with GaAs:Te interfacial layer thickness ranging from 15 Å to 50 Å [<a href="#B19-crystals-08-00445" class="html-bibr">19</a>].</p> Full article ">
21 pages, 4910 KiB  
Review
GaAs Nanowires Grown by Catalyst Epitaxy for High Performance Photovoltaics
by Ying Wang, Xinyuan Zhou, Zaixing Yang, Fengyun Wang, Ning Han, Yunfa Chen and Johnny C. Ho
Crystals 2018, 8(9), 347; https://doi.org/10.3390/cryst8090347 - 29 Aug 2018
Cited by 8 | Viewed by 5172
Abstract
Photovoltaics (PVs) based on nanostructured III/V semiconductors can potentially reduce the material usage and increase the light-to-electricity conversion efficiency, which are anticipated to make a significant impact on the next-generation solar cells. In particular, GaAs nanowire (NW) is one of the most promising [...] Read more.
Photovoltaics (PVs) based on nanostructured III/V semiconductors can potentially reduce the material usage and increase the light-to-electricity conversion efficiency, which are anticipated to make a significant impact on the next-generation solar cells. In particular, GaAs nanowire (NW) is one of the most promising III/V nanomaterials for PVs due to its ideal bandgap and excellent light absorption efficiency. In order to achieve large-scale practical PV applications, further controllability in the NW growth and device fabrication is still needed for the efficiency improvement. This article reviews the recent development in GaAs NW-based PVs with an emphasis on cost-effectively synthesis of GaAs NWs, device design and corresponding performance measurement. We first discuss the available manipulated growth methods of GaAs NWs, such as the catalytic vapor-liquid-solid (VLS) and vapor-solid-solid (VSS) epitaxial growth, followed by the catalyst-controlled engineering process, and typical crystal structure and orientation of resulted NWs. The structure-property relationships are also discussed for achieving the optimal PV performance. At the same time, important device issues are as well summarized, including the light absorption, tunnel junctions and contact configuration. Towards the end, we survey the reported performance data and make some remarks on the challenges for current nanostructured PVs. These results not only lay the ground to considerably achieve the higher efficiencies in GaAs NW-based PVs but also open up great opportunities for the future low-cost smart solar energy harvesting devices. Full article
(This article belongs to the Special Issue III-V Heteroepitaxy for Solar Energy Conversion)
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Figure 1

Figure 1
<p>Relationship between power conversion efficiency, module areal costs, and cost per peak watt (in <span>$</span>/Wp). The light blue line represents the current laboratory record efficiency for bulk crystal silicon while the blue horizontal line is the Shockley-Queisser limit for single-junction devices. Third-generation device concepts increase the limiting efficiency (the limit for multiple exciton generation (MEG) is indicated as the green line). The thermodynamic limit at 1 sun is shown as the red line at 67% and can be reached by an infinite stack of p-n junctions. For next-generation technologies the goal is to reach 0.03–0.05 <span>$</span>/kWh, denoted by the blue shaded region. Adapted with permission from [<a href="#B12-crystals-08-00347" class="html-bibr">12</a>].</p> Full article ">Figure 2
<p>(<b>a</b>) Schematic illustration of the catalytic chemical vapor deposition (CVD) growth of GaAs nanowires (NWs) and (<b>b</b>) the temperature profiles. The typical dual-zone horizontal tube furnace, one zone is used for the solid source (upstream) and the other for the sample (downstream). Adapted with permission from [<a href="#B98-crystals-08-00347" class="html-bibr">98</a>].</p> Full article ">Figure 3
<p>NiGa catalyst and GaAs NW epitaxy relationships. (<b>a</b>) NiGa(110)|GaAs(111), (<b>b</b>) NiGa(111)|GaAs(111) and (<b>c</b>) NiGa(210)|GaAs(110). (<b>d</b>–<b>f</b>) are the schematics of relationship in (<b>a</b>–<b>c</b>). Adapted with permission from [<a href="#B100-crystals-08-00347" class="html-bibr">100</a>].</p> Full article ">Figure 4
<p>Schottky barriers of the catalyst/NW interface. (<b>a</b>,<b>c</b>) Typical I–V characteristics, scanning electron microscope (SEM) image and energy band diagram of the single GaAs NW photovoltaic device with Ni and the Au–Ga alloy tip. (<b>b</b>,<b>d</b>) I–V characteristics, SEM image and energy band diagram of the NW photovoltaic device with deposited Ni and Au. (<b>e</b>,<b>f</b>) device SEM and I–V curves of the Ga/GaAs interface. Adapted with permission from [<a href="#B58-crystals-08-00347" class="html-bibr">58</a>,<a href="#B122-crystals-08-00347" class="html-bibr">122</a>].</p> Full article ">Figure 5
<p>Supersaturation-controlled growth of GaAs NWs. (<b>a</b>) Growth direction statistics of grown GaAs NWs. (<b>b</b>) Simulation of the Ga supersaturation in Au nanoparticles with various diameters (black line) and the experimental results of catalytic Ga concentration with different NW diameters (red line). (<b>c</b>) The schematic illustration of GaAs NW growth rate, density, orientation, and crystal phase change with Ga supersaturation in Au catalyst with different diameters. Adapted with permission from [<a href="#B94-crystals-08-00347" class="html-bibr">94</a>].</p> Full article ">Figure 6
<p>Comparison of the single-step and two-step growth method. (<b>a</b>,<b>b</b>) SEM images of the single-step and two-step grown NWs. Insets: the corresponding cross-sectional SEM images illustrating the length of the NWs. (<b>c</b>,<b>d</b>) Diameter distribution and NW growth orientation statistic of GaAs NWs grown by the 12 nm thick Au catalyst. (<b>e</b>) Room temperature photoluminescence (PL) spectra, showing a good crystal quality of the two-step grown NWs. (<b>f</b>) Cross-sectional view of NWs with the corresponding crystal quality and equilibrium energy band diagram at the zero gate bias. Adapted with permission from [<a href="#B121-crystals-08-00347" class="html-bibr">121</a>].</p> Full article ">Figure 7
<p>Correlation of structure and properties of GaAs NWs. (<b>a</b>–<b>c</b>) In situ measurement of the as-grown individual GaAs NW within a dual-beam SEM system. The I–V characteristics of selected NWs were measured through a tungsten tip brought into contact with the top of the NW, whereas the structural information was revealed by n-XRD on the same NW using focused synchrotron radiation. (<b>d</b>–<b>f</b>) Crystal orientation controlled PV properties of multilayer GaAs NW arrays. (<b>d</b>) Schematic illustration of the PV device structure and the corresponding energy band diagram. (<b>e</b>) XRD patterns collected of the three-layer GaAs NW parallel arrays. The growth directions of NWs were evaluated by XRD before the fabrication of corresponding parallel NW array based Schottky PV devices. (<b>f</b>) The PV performance fabricated with different mixing ratios of &lt;111&gt;- and &lt;110&gt;-oriented NWs. Adapted with permission from [<a href="#B131-crystals-08-00347" class="html-bibr">131</a>,<a href="#B132-crystals-08-00347" class="html-bibr">132</a>].</p> Full article ">Figure 8
<p>Simulated and experimental light absorption of a horizontal and vertical GaAs NW. (<b>a</b>,<b>b</b>) Sketch of the simulated GaAs NW lying on a planar substrate and the 2D-simulation geometry. (<b>c</b>) The external quantum efficiency (EQE)/internal quantum efficiency (IQE) ratio of GaAs NW in dependence of NW diameter. (<b>d</b>) Schematic of the vertical single GaAs NW based solar cell. (<b>e</b>) EQE (normalized by indicated projected area) for both horizontal and vertical GaAs NW solar cell. Adapted with permission from [<a href="#B72-crystals-08-00347" class="html-bibr">72</a>,<a href="#B73-crystals-08-00347" class="html-bibr">73</a>,<a href="#B74-crystals-08-00347" class="html-bibr">74</a>].</p> Full article ">Figure 9
<p>Structure and characteristics of transparent GaAs NW and NW array Schottky photovoltaic devices. (<b>a</b>) Open circuit voltage dependence on the work function difference of the asymmetric Schottky electrodes, (<b>b</b>) IV curves of one typical GaAs NW PV device, (<b>c</b>) schematic of cascaded GaAs NW device structure and band diagram, (<b>d</b>) optical microscope image showing a real test tandem (nine-cell connected in parallel) photovoltaic device, (<b>e</b>) photograph showing the optical transparency of the NW device constructed on glass, (<b>f</b>) I–V curves of the transparent photovoltaic devices composed of two, three, four, six, and nine cells in parallel. Adapted with permission from [<a href="#B81-crystals-08-00347" class="html-bibr">81</a>].</p> Full article ">
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