High efficiency concentrator solar cells (original) (raw)
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Solar Energy Materials and Solar Cells, 2010
Future terrestrial concentrator cells will likely feature four or more junctions. The better division of the solar spectrum and the lower current densities in these new multijunction cells reduce the resistive power loss (I 2 R) and provide a significant advantage in achieving higher efficiency of 45% to 50%. The component subcells of these concentrator cells will likely utilize new technology pathways such as highly metamorphic materials, inverted crystal growth, direct-wafer bonding, and their combinations to achieve the desired bandgaps while maintaining excellent device material quality for optimal solar energy conversion. Here we report preliminary results of two technical approaches: (1) metamorphic ~1-eV GaInAs subcells in conjunction with inverted growth approach and (2) multijunction cells on wafer-bonded, layer transferred epitaxial templates.
III–V multijunction solar cells for concentrating photovoltaics
Energy & Environmental Science, 2009
Concerns about the changing environment and fossil fuel depletion have prompted much controversy and scrutiny. One way to address these issues is to use concentrating photovoltaics (CPV) as an alternate source for energy production. Multijunction solar cells built from III-V semiconductors are being evaluated globally in CPV systems designed to supplement electricity generation for utility companies. The high efficiency of III-V multijunction concentrator cells, with demonstrated efficiency over 40% since 2006, strongly reduces the cost of CPV systems, and makes III-V multijunction cells the technology of choice for most concentrator systems today. In designing multijunction cells, consideration must be given to the epitaxial growth of structures so that the lattice parameter between material systems is compatible for enhancing device performance. Low resistance metal contacts are crucial for attaining high performance. Optimization of the front metal grid pattern is required to maximize light absorption and minimize I 2 R losses in the gridlines and the semiconductor sheet. Understanding how a multijunction device works is important for the design of next-generation high efficiency solar cells, which need to operate in the 45%-50% range for a CPV system to make better economical sense. However, the survivability of solar cells in the field is of chief concern, and accelerated tests must be conducted to assess the reliability of devices during operation in CPV systems. These topics are the focus of this review.
Multi-junction III–V solar cells: current status and future potential
Solar Energy, 2005
Our recent R&D activities of III-V compound multi-junction (MJ) solar cells are presented. Conversion efficiency of InGaP/InGaAs/Ge has been improved up to 31-32% (AM1.5) as a result of technologies development such as double hetero-wide band-gap tunnel junction, InGaP-Ge hetero-face structure bottom cell, and precise lattice-matching of InGaAs middle cell to Ge substrate by adding indium into the conventional GaAs layer. For concentrator applications, grid structure has been designed in order to reduce the energy loss due to series resistance, and world-record efficiency InGaP/InGaAs/Ge 3-junction concentrator solar cell with an efficiency of 37.4% (AM1.5G, 200-suns) has been fabricated. In addition, we have also demonstrated high-efficiency and large-area (7000 cm 2) concentrator InGaP/InGaAs/ Ge 3-junction solar cell modules of an outdoor efficiency of 27% as a result of developing high-efficiency InGaP/InG-aAs/Ge 3-junction cells, low optical loss Fresnel lens and homogenizers, and designing high thermal conductivity modules. Future prospects are also presented. We have proposed concentrator III-V compound MJ solar cells as the 3rd generation solar cells in addition to 1st generation crystalline Si solar cells and 2nd generation thin-film solar cells. We are now developing low-cost and high output power concentrator MJ solar cell modules with an output power of 400 W/m 2 for terrestrial applications.
Raising the Efficiency Ceiling with Multijunction III-V Concentrator Photovoltaics
2008
In this paper, we look at the question "how high can solar cell efficiency go?" from both theoretical and experimental perspectives. First-principle efficiency limits are analyzed for some of the main candidates for high-efficiency multijunction terrestrial concentrator cells. Many of these cell designs use lattice-mismatched, or metamorphic semiconductor materials in order to tune subcell band gaps to the solar spectrum. Minority-carrier recombination at dislocations is characterized in GaInAs inverted metamorphic solar cells, with band gap ranging from 1.4 to 0.84 eV, by light I-V, electron-beam-induced current (EBIC), and cathodoluminescence (CL). Metamorphic solar cells with a 3-junction GaInP/ GaInAs/ Ge structure were the first cells to reach over 40% efficiency, with an independently confirmed efficiency of 40.7% (AM1.5D, low-AOD, 240 suns, 25°C). The high efficiency of present III-V multijunction cells now in high-volume production, and still higher efficiencies of...
Advances in High-Efficiency III-V Multijunction Solar Cells
Advances in OptoElectronics, 2007
The high efficiency of multijunction concentrator cells has the potential to revolutionize the cost structure of photovoltaic electricity generation. Advances in the design of metamorphic subcells to reduce carrier recombination and increase voltage, wide-band-gap tunnel junctions capable of operating at high concentration, metamorphic buffers to transition from the substrate lattice constant to that of the epitaxial subcells, concentrator cell AR coating and grid design, and integration into 3-junction cells with current-matched subcells under the terrestrial spectrum have resulted in new heights in solar cell performance. A metamorphicGa0.44In0.56P/Ga0.92In0.08As/ Ge 3-junction solar cell from this research has reached a record 40.7% efficiency at 240 suns, under the standard reporting spectrum for terrestrial concentrator cells (AM1.5 direct, low-AOD, 24.0W/cm2,25∘C), and experimental lattice-matched 3-junction cells have now also achieved over 40% efficiency, with 40.1% measured...
Concentrator and Space Applications of High-Efficiency Solar Cells-Recent Developments
1998
GaInP/GaAs cells invented and developed at NREL have achieved world-record efficiencies. We estimate that their production for space applications has grown to > $100 million/yr. Approximately 300 MW/yr of 1000X terrestrial concentrator cells could be fabricated with the existing manufacturing capacity at a cost of about 21{cents}/Wp. A resurgence of interest in terrestrial PV concentrators, together with the strength of the III-V space-solar-cell industry, indicate that III-V cells are also attractive for terrestrial applications.
Toward Stationary Concentrator Photovoltaic Panels
2017
Growth of GaSb with low threading dislocation density directly on GaAs may be possible with the strategic strain relaxation of interfacial mist arrays. This creates an opportunity for a multi-junction solar cell with access to a wide range of well-developed direct bandgap materials. Multi-junction cells with a single layer of GaSb/GaAs interfacial mist arrays could achieve higher eciency than state-of-the-art inverted metamorphic multi-junction cells while forgoing the need for costly compositionally graded buer layers. To develop this technology, GaSb single junction cells were grown via molecular beam epitaxy on both GaSb and GaAs substrates to compare homoepitaxial and heteroepitaxial GaSb device results. The GaSb-on-GaSb cell had an AM1.5g eciency of 5.5% and a 44-sun AM1.5d eciency of 8.9%. The GaSb-on-GaAs cell was 1.0% ecient under AM1.5g and 4.5% at 44 suns. The lower performance of the heteroepitaxial cell was due to low minority carrier Shockley-Read-Hall lifetimes and bulk shunting caused by defects related to the mismatched growth. A physics-based device simulator was used to create an inverted triple-junction GaInP/GaAs/GaSb model. The model predicted that, with current GaSb-on-GaAs material quality, the not-current-matched, proof-of-concept cell would provide 0.5% absolute eciency gain over a tandem GaInP/GaAs cell at 1 sun and 2.5% gain at 44 suns, indicating that the eectiveness of the GaSb junction was a function of concentration. The state-of-the-art single-substrate multi-junction solar cell is the inverted metamorphic (IMM) cell, where lattice mismatched subcells are grown monolithically via compositionally graded buer layers. 13 Growth of a typical triple-junction (3-J) IMM starts with a GaAs (lattice
Energy Procedia, 2012
This paper reviews Japanese R&D activities of III-V compound multi-junction (MJ) and concentrator solar cells. As a result of advanced technologies development for high efficiency cells and discovery of superior radiation-resistance of InGaP based materials, InGaP-based MJ solar cells have been commercialised for space use in Japan. A new world-record efficiency of 35.8% at 1 sun has been achieved with InGaP/GaAs/InGaAs 3-junction solar cell. MJ solar cells composing of multi-layers with different bandgap energies have the potential for achieving high conversion efficiencies of over 50% and are promising for space and terrestrial applications due to wide photo response. In order to solve the problems of difficulties in making high performance and stable tunnel junctions, a double hetero (DH) structure tunnel junction was found to be useful for preventing diffusion from the tunnel junction and improving the tunnel junction performance by the authors. An InGaP material instead of AlGaAs for the top cell was proposed by NREL. As a result of advanced technologies development for high efficiency cells and discovery of superior radiation-resistance of InGaP-based materials by the authors, InGaP-based MJ solar cells have been commercialised for space use even in Japan since 2002. Most recently, world-record efficiency (35.8%) at 1-sun AM1.5G has been realised with inverted epitaxial grown InGaP/GaAs/InGaAs 3-junction cells by Sharp. Since the concentrator modules have been demonstrated to produce roughly 1.7 to 2.6 times more energy per area per annum than the 14 % multicrystalline silicon modules in most cities in Japan, concentrator PV (Photovoltaics) as the 3 rd PV technologies in addition to the 1 st crystalline Si PV and the 2 nd thin-film PV technologies are expected to contribute to electricity cost reduction for widespread PV applications.
High-Efficiency Solar Cell Concepts: Physics, Materials, and Devices
2005
Over the past three decades, significant progress has been made in the area of high-efficiency multijunction solar cells, with the effort primarily directed at current-matched solar cells in tandem. The key materials issues here have been obtaining semiconductors with the required bandgaps for sequential absorption of light in the solar spectrum and that are lattice matched to readily available substrates. The GaInP/GaAs/Ge cell is a striking example of success achieved in this area. Recently, several new approaches for high-efficiency solar cell design have emerged, that involve novel methods for tailoring alloy bandgaps, as well as alternate technologies for hetero-epitaxy of III-V's on Si. The advantages and difficulties expected to be encountered with each approach will be discussed, addressing both the materials issues and device physics whilst contrasting them with other fourth-generation solar cell concepts.
Recent developments in multijunction solar cell research
Solar Cells, 1988
Power conversion efficiencies as high as 16.5% under 1 Sun, air mass 1.5 (AM 1.5) illumination have been obtained for three-terminal, two-junction 1.72 eV A1GaAs/1.15 eV GaInAs monolithic cascade solar cells. The structures were grown by metal-organic chemical vapor deposition. The increased efficiencies arise primarily from improved surface morphology in this lattice-mismatched materials system. For the individual subcells in a cascade configuratiori, 1 Sun, AM 1.5 efficiencies as high as 10.4% and 15.3% are obtained for 1.15 eV GaInAs and 1.72 eV A1GaAs, projecting an eventual efficiency of 25.7% for the corresponding two-junction stack. Under 400 Sun concentration, these values are projected to increase to 12%, 19% and 31% respectively.