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ABSTRACT: Emcore Photovoltaics has been in volume production of high-efficiency multi-junction solar cells for spacecraft applications since 1999. Emcore's current heritage product is the advanced triple-junction (ATJ) n/p InGaP/InGaAs/Ge solar cell. The ATJ cell exhibits a beginning-of-life (BOL) minimum average conversion efficiency of 27.5%, under air-mass zero (AM0) illumination conditions, making it the highest efficiency flight cell available in the market to date. The efficiencies of flight cells in a ship lot range from approximately 26.0% to 29.5%. A new version of the ATJ cell that is also in volume production at Emcore, incorporates a monolithically integrated p/n GaAs bypass diode. This cell is called the ATJM. Using the ATJM cell as the baseline platform, an optimized solar cell is being developed that is mechanically identical to the heritage ATJM cell, but exhibiting a minimum average efficiency of about 28.5%. The development lots of this 2nd generation ATJM exhibit typical BOL performance parameters of Voc of 2,650 mV, Jsc of 17.3 mA/cm/sup 2/, and fill factor of 84%, under illuminated AM0 conditions. In this paper, the manufacturing aspects of the ATJ & ATJM cells, as well as, the development aspects of the 2nd generation ATJM solar cells will be presented.
Photovoltaic Energy Conversion, 2003. Proceedings of 3rd World Conference on; 06/2003
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ABSTRACT: The electrical performance and space qualification data of very
high efficiency dual junction n/p InGaP/GaAs (on Ge) solar cells
manufactured at Emcore Photovoltaics are described. The minimum average
beginning-of-life (BOL) conversion efficiency of large area (27.5
cm<sup>2</sup>) solar cells currently in production is 23.0% (28°C,
1 sum AM0, 135.3 mW/cm<sup>2</sup>). The resulting power output per cell
is 0.86 watts. The highest efficiency obtained of 25.3% represents a
record for a large area dual junction cell. The results presented here
are for solar cells that have an optimized end-of-life (EOL) structure.
The power remaining factors after irradiation with 1-MeV electrons at
fluences of 5E14, 1E15, and 3E15 e/cm<sup>2</sup> are 0.89, 0.84, and
0.74 respectively. The results of full space qualification testing
including electrical, radiation exposure, temperature coefficients,
thermal cycling, humidity, optical, and mechanical measurements are
presented
Photovoltaic Specialists Conference, 2000. Conference Record of the Twenty-Eighth IEEE; 02/2000
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ABSTRACT: The authors report the design and testing of extremely
radiation-hard high-efficiency large-area InGaP/GaAs/Ge triple-junction
solar cells. The solar cell junctions are designed for longer minority
carrier diffusion lengths after particle irradiation. The power
remaining factors after 5E14 and 1E15 electrons/cm<sup>2</sup> 1-MeV
electron radiation are 92% and 87.5%, respectively. These results are
highest reported to date and are extremely desirable for electrical
power design of the spacecraft. Furthermore, the InGaP/GaAs/Ge
triple-junction solar cells are currently in production at EMCORE
Photovoltaics. Minimum average AM0 efficiency for the large-area fight
cells is 26%, with efficiencies as high as 27% demonstrated for a large
number of cells
Photovoltaic Specialists Conference, 2000. Conference Record of the Twenty-Eighth IEEE; 02/2000
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ABSTRACT: A monolithic interconnected module (MIM) structure has been
developed for thermophotovoltaic (TPV) applications. The MIM device
consists of many individual InGaAs cells series-connected on a single
semi-insulating InP substrate. An infrared (IR) back surface reflector
(BSR), placed on the rear surface of the substrate, returns the unused
portion of the TPV radiator output spectrum back to the radiator for
recuperation, thereby providing for high system efficiencies. Also, the
use of a BSR reduces the requirements imposed on a front surface
interference filter and may lead to using only an anti-reflection
coating. As a result, MIMs are exposed to the entire radiator output,
and with increasing output power density. MIMs were fabricated with an
active area of 0.9×1 cm, and with 15 cells monolithically
connected in series. Both lattice-matched and lattice-mismatched
InGaAs/InP devices were fabricated, with bandgaps of 0.74 and 0.55 eV,
respectively. The 0.74 eV MIMs demonstrated an open-circuit voltage
(Voc) of 6.16 V and a fill factor of 74.2% at a short-circuit current
(Jsc) of 0.84 A/cm<sup>2</sup>, under flashlamp testing. The 0.55 eV
modules demonstrated a Voc of 4.85 V and a fill factor of 57.8% at a Jsc
of 3.87 A/cm<sup>2</sup>. The near IR reflectance (2-4 μm) for both
lattice-matched and lattice-mismatched structures was measured to be in
the range of 80-85%. Latest electrical and optical performance results
for these MIMs is presented
Photovoltaic Specialists Conference, 1997., Conference Record of the Twenty-Sixth IEEE; 11/1997
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R.W. Hoffman Jr, N.S. Fatemi,
P.P. Jenkins,
V.G. Weizer,
M.A. Stan,
S.A. Ringel,
D.A. Scheiman,
D.M. Wilt,
D.J. Brinker,
R.J. Walters,
S.R. Messenger
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ABSTRACT: The high electrical conversion performance and radiation
resistance of InP solar cells were discovered during the last decade.
The combination of these two characteristics make InP a very attractive
material for space solar cells. To date, the best performance results
for both homo-epitaxial and hetero-epitaxial InP solar cells were
achieved using a n/p configuration. The p/n configuration is desirable
for hetero-epitaxial growth on inexpensive, strong, light weight, group
IV substrates such as Si and Ge. We have succeeded in developing p/n
configuration homo-epitaxy InP solar cells with begining-of-life AM0
efficiency values exceeding 17.6%. The high efficiency values resulted
from improved emitter performance due to a reduction of Zn interstitial
defects in the p-type emitter. Preliminary 3 MeV proton irradiation
resistance data are presented which show the high efficiency p/n cells
retain 75% of begining-of-life power after 7×10<sup>11</sup>
protons/cm<sup>2</sup> fluence
Photovoltaic Specialists Conference, 1997., Conference Record of the Twenty-Sixth IEEE; 11/1997
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ABSTRACT: Thermophotovoltaic (TPV) converters were developed and tested at
the heat source operating temperature of 1700 K. Rare-earth-doped
yttrium aluminum garnet (YAG) and lutetium yttrium aluminum garnet (Lu,
YAG) selective emitters, as well as a blackbody emitter, were coupled to
InGaAs/InP photovoltaic (PV) cells and bandpass/infrared (IR) reflector
filters. YAG-based selective emitters were doped with Ho, Tm, and Er. PV
cells had bandgaps of 0.51, 0.57, and 0.69 eV. Converter energy
conversion efficiencies approaching 30%, as well as electrical output
power densities near 2 W/cm<sup>2</sup> were demonstrated. The overall
performance of the filtered blackbody-based converter was found to be
superior to the selective emitter YAG-based converters. The details of
the measurements performed on the above converters and their individual
components are presented
Energy Conversion Engineering Conference, 1996. IECEC 96. Proceedings of the 31st Intersociety; 09/1996
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ABSTRACT: Components of a solar thermophotovoltaic (STPV) power system have
been developed and tested. This paper describes the principle of
operation of a STPV system, the conceptual design of the TPV conversion
unit, and some of the operating features which make it attractive for
both space and terrestrial application. McDonnell Douglas Aerospace
(MDA) conducted over 600 hrs. Of on-sun tests and reached temperatures
above 1573 K during these tests. Essential Research has developed and
tested selective emitter and blackbody-based TPV converters with
efficiencies approaching 30%. Analytical models developed by MDA and
Essential Research were validated by test data and used to develop a
conceptual design and to estimate the system performance. These models
indicate the efficiency of a STPV power conversion system to be greater
than 20% using current state-of-the-art technology and could increase to
above 35% using advance technology
Photovoltaic Specialists Conference, 1996., Conference Record of the Twenty Fifth IEEE; 06/1996
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ABSTRACT: A contact system for use on the n<sup>+</sup> InP window layer of
an InP/InGaAs/InP thermophotovoltaic (TPV) cell is described. The
contact system, composed of an Au-7 at.% Ge mixture, exhibits very low
contact resistivity values on both lattice matched and lattice
mismatched heterostructures without the need for contact sintering.
Specific contact resistivity values in the low 10<sup>-6</sup>
Ω-cm<sup>2</sup> range are achieved (without sintering) for the
lattice matched devices. For the lattice mismatched devices resistivity
values approaching the theoretical minimum value in the mid 10<sup>-8
</sup> Ω-cm<sup>2</sup> range are achieved, again without
sintering
Photovoltaic Specialists Conference, 1996., Conference Record of the Twenty Fifth IEEE; 06/1996
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ABSTRACT: We have developed high efficiency p<sup>+</sup>/n/n<sup>+</sup>
homoepitaxial InP space solar cells with the intent of applying the
technology to hetero-epitaxial InP cell growth on Ge or Si substrates.
Our cell design eliminates the use of InGaAs contact layers under the
front grid metallization. A p<sup>+</sup>/n/n<sup>+</sup> cell
demonstrated a conversion efficiency of 16.2% under AM0, 1 sun, 25°C
conditions. Cell performance instabilities were observed as a function
of aging and light soaking. Hydrogen incorporated during cool-down from
OMVPE growth temperature may have been responsible for the observed
instabilities. Conversion efficiency values exceeding 18% are expected
with minor alterations to our cell design
Photovoltaic Specialists Conference, 1996., Conference Record of the Twenty Fifth IEEE; 06/1996
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ABSTRACT: This paper describes the status of development of an indium
gallium arsenide (InGaAs) monolithically-interconnected module (MIM) for
thermophotovoltaic (TPV) energy conversion applications. The MIM
structure features series interconnected InGaAs sub-cells on an
insulating indium phosphide (InP) substrate, with a rear-surface
infrared (IR) reflector. Motivations for developing the MIM structure
include: reduced resistive losses; higher output power density; improved
thermal coupling; and, ultimately, higher system efficiency. An optical
model has been developed, free carrier absorption coefficients have been
measured and a prototype MIM device has been demonstrated. A rear
surface IR reflector has been developed with ~98% reflectance in the
sub-bandgap (>1.7 μm) region
Photovoltaic Specialists Conference, 1996., Conference Record of the Twenty Fifth IEEE; 06/1996
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ABSTRACT: Two contact systems for use on shallow junction InP solar cells are described. The feature shared by these two contact systems is the absence of the metallurgical intermixing that normally takes place between the semiconductor and the contact metallization during the sintering process. The n(+)pp(+) cell contact system, consisting of a combination of Au and Ge, not only exhibits very low resistance in the as-fabricated state, but also yields post-sinter resistivity values of 1(exp -7) ohms-sq cm, with effectively no metal-InP interdiffusion. The n(+)pp(+)cell contact system, consisting of a combination of Ag and Zn, permits low resistance ohmic contact to be made directly to a shallow junction p/n InP device without harming the device itself during the contacting process.
10/1995;
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ABSTRACT: Low bandgap photovoltaic devices are required for the development of thermophotovoltaic power conversion at moderate temperatures. We have produced In<sub>x</sub>Ga<sub>1-x</sub>As photovoltaic n/p devices on InP with bandgaps ranging from 0.75 eV to 0.60 eV. Testing under a filtered 1500°K blackbody emitter, the 0.75 eV displayed an 18.3% conversion efficiency and the 0.60 eV device had a 6% efficiency. The devices were also tested at temperatures ranging from 25°C to 100°C. The temperature coefficient of output power increased dramatically as the bandgap decreased. Testing under rare-earth doped YAG selective emitters demonstrated the ability of these emitters to produce narrow spectral emissions
Photovoltaic Energy Conversion, 1994., Conference Record of the Twenty Fourth. IEEE Photovoltaic Specialists Conference - 1994, 1994 IEEE First World Conference on; 01/1995
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ABSTRACT: Recently, we have succeeded in fabricating diffused junction p(+)n(Cd,S) InP solar cells with measured AMO, 25 C open circuit voltage (V(sub OC)) of 887.6 mV, which, to the best of our knowledge, is higher than previously reported V(sub OC) values for any InP homojunction solar cells. The experiment-based projected achievable efficiency of these cells using LEC grown substrates is 21.3%. The maximum AMO, 25 C efficiency recorded to date on bare cells is, however, only 13.2%. This is because of large external and internal losses due to non-optimized front grid design, antireflection (AR) coating and emitter thickness. This paper summarizes recent advances in the technology of fabrication of p(+)n InP diffused structures and solar cells, resulted from a study undertaken in an effort to increase the cell efficiency. The topics discussed in this paper include advances in: 1) the formation of thin p(+) InP:Cd emitter layers, 2) electroplated front contacts, 3) surface passivation and 4) the design of a new native oxide/AI203/MgF2 three layer AR coating using a chemically-grown P-rich passivating oxide as a first layer. Based on the high radiation resistance and the excellent post-irradiation annealing and recovery demonstrated in the early tests done to date, as well as the projected high efficiency and low-cost high-volume fabricability, these cells show a very good potential for space photovoltaic applications.
10/1994;
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ABSTRACT: Contact formation to InP is plagued by violent metal-semiconductor
intermixing that takes place during the contact sintering process.
Because of this the InP solar cell cannot be sintered after contact
deposition. This results in cell contact resistances that are orders of
magnitude higher than those that could be achieved if sintering could be
performed in a nondestructive manner. The authors report on a truly
unique contact system, involving Au and Ge, which is easily fabricated,
which exhibits extremely low values of contact resistivity, and in which
there is virtually no metal-semiconductor interdiffusion, even after
extended sintering. they present a description of this contact system
and suggest possible mechanisms to explain the observed behavior
Photovoltaic Specialists Conference, 1993., Conference Record of the Twenty Third IEEE; 06/1993
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[show abstract]
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ABSTRACT: Contact formation to InP is plagued by violent metal-semiconductor intermixing that takes place during the contact sintering process. Because of this the InP solar cell cannot be sintered after contact deposition. This results in cell contact resistances that are orders of magnitude higher than those that could be achieved if sintering could be performed in a non-destructive manner. We report here on a truly unique contact system involving Au and Ge, which is easily fabricated, which exhibits extremely low values of contact resistivity, and in which there is virtually no metal-semiconductor interdiffusion, even after extended sintering. We present a description of this contact system and suggest possible mechanisms to explain the observed behavior.
06/1993;
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ABSTRACT: Five Au–Ga alloys have been studied using x‐ray photoelectron spectroscopy as part of the program to determine alloy effects on core level binding energies and identify thin film and bulk compositions of unknown Au x Ga y alloys. The binding energies and peak intensities of the Au 4f, Ga 2p 3/2 , Ga 3p 3/2 , and Ga LMM core levels were determined for pure Au and Ga along with bulk alloy compositions of α‐Au 0.88 Ga 0.12 , β‐Au 0.78 Ga 0.22 , γ‐Au 9 Ga 4 , AuGa, and AuGa 2 . These values were determined for surfaces scraped in situ to expose the bulk composition. The Au 4f 7/2 binding energies were 83.95 eV for pure Au and 84.4, 84.6, 84.9, 85.2, and 85.5 eV for each of the respective alloys, while the Ga core levels and Auger energy shifted less than 0.3 eV over the range of alloy compositions. These results exhibit the same trend as the previously studied Au–In system and furnish calibration values that allow determination of the composition of unknown alloys.
Journal of Vacuum Science & Technology A Vacuum Surfaces and Films 08/1992; · 1.25 Impact Factor
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[show abstract]
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ABSTRACT: The authors describe two contact systems that provide low contact
resistance to InP solar cells that do not require subjecting the
current-carrying metallization to a postdeposition sintering process. It
is shown that these two systems, one nickel-based and the other
silver-based, provide contact resistivity ( R <sub>c</sub>)
values in the low 10<sup>-6</sup>-Ω-cm<sup>2</sup> range, as
fabricated, without the need for sintering. It is demonstrated that it
is possible to achieve specific contact resistivities in the low
10<sup>-6</sup>-Ω-cm<sup>2</sup> range without compromising
emitter integrity through the introduction of any of a number of
metal-phosphide interlayers, including Ni<sub>3</sub>P, AgP<sub>2</sub>,
and Au<sub>2</sub>P<sub>3</sub>
Indium Phosphide and Related Materials, 1992., Fourth International Conference on; 05/1992
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ABSTRACT: In SPRAT XI, we proposed that p(sup +)n diffused junction InP solar cells should exhibit a higher conversion efficiency than their n(sup +)p counterparts. This was mainly due to the fact that our p(sup +)n (Cd,S) cell structures consistently showed higher V (sub OC) values than our n(sup +)p (S,Cd) structures. The highest V(sub OC) obtained with the p(sup +)n (Cd,S) cell configuration was 860 mV, as compared to the highest V(sub OC) 840 mV obtained with the n(sup +)p (S,Cd) configuration (AMO, 25 C). In this work, we present the performance results of our most recent thermally diffused cells using the p(sup +)n (Cd,S) structure. We have been able to fabricate cells with V(sub OC) values approaching 880 mV. Our best cell with an unoptimized front contact grid design (GS greater than or equal to 10%) showed a conversion efficiency of 13.4% (AMO, 25 C) without an AR coating layer. The emitter surface was passivated by a -50A P rich oxide. Achievement of such high V(sub OC) values was primarily due to the fabrication of emitter surfaces, having EPD densities as low as 2E2 cm(sup -2) and N(sub a)N(sub d) of about 3E18 cm (sup -3). In addition, our preliminary investigation of p(sup +)n structures seem to suggest that Cd-doped emitter cells are more radiation resistant than Zn-doped emitter cells against both high energy electron and proton irradiation.
02/1992;
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ABSTRACT: The possibility of providing low-resistance contacts to
shallow-junction InP solar cells which do not require sintering and
which do not cause device degradation even when subjected to extended
annealing at elevated temperatures is investigated. It is shown that the
addition of In to Au contacts in amounts that exceed the solid
solubility limit lowers the as-fabricated (unsintered) contact
resistivity R <sub>c</sub> to the 10<sup>-5</sup> ohm-cm<sup>2
</sup> range. Consideration is also given to the contact system Au/Au
<sub>2</sub>P<sub>3</sub> which has been shown to exhibit as-fabricated
R <sub>c</sub> values in the 10<sup>-6</sup> ohm-cm<sup>2</sup>
range, but which fails quickly when heated. It is shown that the
substitution of a refractory metal (W, Ta) for Au preserves the low
R <sub>c</sub> values while preventing the destructive reactions
that would normally take place in this system at high temperatures
Photovoltaic Specialists Conference, 1991., Conference Record of the Twenty Second IEEE; 11/1991
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ABSTRACT: The current state of profile etching in GaAs and InP is
summarized, including data on novel geometries attainable as a function
of etchant temperature, composition, and rate, substrate orientation and
carrier concentration, and oxide thickness between substrate and
photoresist. V-grooved solar cells have been manufactured with both GaAs
and InP, and the improved optical absorption demonstrated. Preferred
parameters for various applications are listed and discussed
Photovoltaic Specialists Conference, 1991., Conference Record of the Twenty Second IEEE; 11/1991
