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.
1 Introduction
The rising cost of producing electricity from fossil fuels is
favorably shifting energy production to renewable resources
such as solar photovoltaics (PV), for example.
1
Increasing
advances in solar cell efficiency and lowering cost endeavors,
along with clean energy initiatives are the primary factors for the
impetus in solar energy production to date. In 2007, the world
production of solar cells reached 3.8 GW with Japan being the
leading producer.
2
The rest of the world with rapidly increasing
development capabilities to manufacture solar cells in mass
quantities contributed to over 70% of the total PV generated in
2007. Market trends indicate that solar cell manufacturing
capacities have been climbing annually at an average greater
than 40% over last 10 years with a 50% leap in 2007 compared to
Dr Cotal received his PhD in
Solid State Physics from
Oklahoma State University. As
a Postdoctoral Fellow he worked
on InP-, GaAs- and Si-based
solar cells at the Naval Research
Laboratory. He leads Spec-
trolab’s terrestrial development
programs for the design, fabri-
cation and testing of III–V
multijunction solar cells. His
interests are in device physics,
device and heat transfer
modeling, SMT of concentrator
cells and terrestrial PV designs
for use in specialized applications. He won R&D 100 (2001 &
2007) and Scientific American 50 (2002) recognition for his
outstanding work in the development of the Triple Junction
Terrestrial Concentrator Solar Cell Technology.
Dr Fetzer is manager of the
MOVPE research and develop-
ment group responsible for the
development of metal–organic
vapor phase epitaxial deposition
processes for advanced solar
cells and photonic devices. He
received his BS in Physics and
PhD in Materials Science and
Engineering from University of
Utah. As an Associate Technical
Fellow at the Boeing Company
he has developed advanced
epitaxial layers of III–V
compound semiconductors.
Before joining Spectrolab in 2001, Dr Fetzer performed research
under Dr G. B. Stringfellow at the University of Utah exploring the
use of surfactant-mediated epitaxy to control ternary alloy
microstructure and the underlying surface physics.
Spectrolab, Inc, Sylmar, California, 91342, USA
174 |
Energy Environ. Sci.
, 2009,
2
, 174–192
This journal is
ª
The Royal Society of Chemistry 2009
REVIEW www.rsc.org/ees
| Energy & Environmental Science
the previous year. Ostensibly, growth in the PV industry is
projected to continue growing through 2010 including PV
installations.
Components such as modules, inverter, tracker, installation
and other balance of systems (BOS) are what typically define an
installed PV system. The burgeoning demand of global PV
installations is driven by the factors mentioned above; however,
not all solar cells produced each year have in the past been
converted to installed PV power. The disparities between PV
produced and installed are due to the lack of more aggressive
solar Renewable Portfolio Standards, the deficiency of more
market incentives, the lack of implementing product and
building regulations, and issues with the supply chain of optical
components.
3–7
Despite this, global PV installations are rising. In
2007, they rose by an average of 46% compared to 2006 with
a finishing year-end total in the range of 2287–2826 MW
according to various reports with one rendition evident in
Fig. 1.
8–10
Most of the power came from Europe, demonstrating
dominance once again in this area. Over 1300 MW of this,
however, was installed in Germany which is still holding a large
section of the industry’s market share for installed PV. The
global cumulative installed PV electricity in 2007 was over 9 GW
which is still an insignificant amount when comparing to the
estimated total power consumption in the world of 18 TW (1.8
10
10
kW).
11,12
The total cumulative power from installed, grid-
tied, concentrating photovoltaics (CPV) in 2007 was over
1.5 MW mostly based on single crystal silicon (Si) solar cells and
multijunction cells from III–V semiconductors.
13–18
Joseph Boisvert was born in
Malden, Massachusetts. He
received his BS from the
Massachusetts Institute of
Technology in 1980 and MS and
PhD degrees from the Univer-
sity of Illinois at Urbana-
Champaign in 1984. Dr Boisvert
is presently a Senior Scientist/
Engineer at Spectrolab, Inc.,
a Boeing Company, where he is
responsible for developing III–V
photodetectors and solar cells.
He has 24 years of experience in
the research and development of
solid-state photodetectors and solar cells, including device and
process design, modeling, test and data analysis. Dr. Boisvert is an
Associate Technical Fellow of the Boeing Company.
Dr Richard R. King is Boeing
Technical Fellow and Principal
Scientist responsible for Photo-
voltaic Cell R&D at Spectrolab.
He received his BS, MS and
PhD degrees at Stanford
University. His photovoltaics
research over the last 20 years
includes work on III–V meta-
morphic materials and devices,
4-, 5-, and 6-junction cells, and
minority-carrier recombination
at heterointerfaces. Dr King led
Spectrolab’s development of
high-efficiency III–V multi-
junction cells, resulting in the first solar cells of any type to reach
over 40% efficiency, and was recognized with R&D 100 awards in
2001 and 2007, and a Scientific American 50 award in 2002. Dr
King was inducted into the Space Technology Hall of Fame in
2004, and has 11 patents and over 90 publications on photovoltaics
and device physics.
Mr Hebert received his BS in
Mechanical Engineering and BA
in Philosophy from the Univer-
sity of Notre Dame, and his
MS in Mechanical Engineering
from Colorado State University.
Mr Hebert performed
manufacturing energy efficiency
audits at the Industrial Assess-
ment Center at Colorado State
while performing his research on
high speed deposition of CdTe
solar cells. Mr Hebert is
a Senior Staff Engineer at
Spectrolab. He has nine years
experience of performing characterization and qualification testing
on multijunction space cells and has received four Hughes Tech-
nical Excellence Awards, a patent and a trade secret. Mr Hebert is
currently leading qualification of the first generation multijunction
terrestrial cells.
Dr N. H. Karam is Vice Presi-
dent of Advanced Technology
Products and has the overall
responsibility for Boeing -
Spectrolab’s internally and
externally funded R&D projects.
He has over 20 years of experi-
ence in materials research,
photovoltaic and optoelectronic
devices, and MOCVD reactor
design. He is currently actively
involved in the development of
advanced space solar cells
through Spectrolab’s jointly
funded Dual Use Science &
Technology program with the Air Force Research Laboratory. Dr
Karam and his Advanced Technology Products Team recently won
the R&D 100 and the Scientific American 50 awards for
contributions in the field of energy generation.
This journal is
ª
The Royal Society of Chemistry 2009
Energy Environ. Sci.
, 2009,
2
, 174–192 | 175
النتائج (
العربية) 1:
[نسخ]نسخ!
وأدت المخاوف من نفاد الوقود الأحفوري والبيئة المتغيرة الكثير من الجدلوالتمحيص. طريقة واحدة لمعالجة هذه القضايا استخدام تركيز وحدات الطاقة الشمسية (الحزب الشيوعي الفيتنامي)الحصول على مصدر بديل لإنتاج الطاقة. مولتيجونكشن الخلايا الشمسية المبنية من أشباه الموصلات الثالث – الخامسويجري تقييم على الصعيد العالمي في نظم الحزب الشيوعي الفيتنامي تهدف إلى تكملة توليد الكهرباء لفائدةالشركات. كفاءة عالية من الخلايا مركزات مولتيجونكشن الثالث – الخامس، مع إثبات الكفاءةأكثر من 40 في المائة منذ عام 2006، بشدة يقلل من تكلفة نظم الحزب الشيوعي الفيتنامي، ويجعل الخلايا مولتيجونكتيون الثالث – الخامسالتكنولوجيا المفضلة لمعظم نظم مركزات اليوم. في تصميم الخلايا مولتيجونكشن،ويجب النظر إلى النمو الفوقي للهياكل حيث أن المعلمة شعرية بيننظم المواد متوافق لتحسين أداء الجهاز. الاتصالات معدنية مقاومة منخفضةأهمية حاسمة لتحقيق الأداء العالي. مطلوب الأمثل لنمط الشبكة المعدنية الجبهة إلىتحقيق أقصى قدر من امتصاص الضوء، والتقليل إلى أدنى حد وأنا2R الخسائر في خطوط الشبكة والورقة أشباه الموصلات.فهم كيف يعمل جهاز مولتيجونكشن مهم لتصميم الجيل القادمالخلايا الشمسية عالية الكفاءة، التي يجب أن تعمل في حدود 45-50% لنظام الحزب الشيوعي الفيتنامي لجعلاقتصادا الشعور بشكل أفضل. ومع ذلك، البقاء على قيد الحياة للخلايا الشمسية في المجال قلق كبير،ويجب أن تجري اختبارات المعجل لتقييم موثوقية الأجهزة أثناء عملية فيCPV systems. These topics are the focus of this review.1 IntroductionThe rising cost of producing electricity from fossil fuels isfavorably shifting energy production to renewable resourcessuch as solar photovoltaics (PV), for example.1Increasingadvances in solar cell efficiency and lowering cost endeavors,along with clean energy initiatives are the primary factors for theimpetus in solar energy production to date. In 2007, the worldproduction of solar cells reached 3.8 GW with Japan being theleading producer.2The rest of the world with rapidly increasingdevelopment capabilities to manufacture solar cells in massquantities contributed to over 70% of the total PV generated in2007. Market trends indicate that solar cell manufacturingcapacities have been climbing annually at an average greaterthan 40% over last 10 years with a 50% leap in 2007 compared toDr Cotal received his PhD inSolid State Physics fromOklahoma State University. Asa Postdoctoral Fellow he workedon InP-, GaAs- and Si-basedsolar cells at the Naval ResearchLaboratory. He leads Spec-trolab’s terrestrial developmentprograms for the design, fabri-cation and testing of III–Vmultijunction solar cells. Hisinterests are in device physics,device and heat transfermodeling, SMT of concentratorcells and terrestrial PV designsfor use in specialized applications. He won R&D 100 (2001 &2007) and Scientific American 50 (2002) recognition for hisoutstanding work in the development of the Triple JunctionTerrestrial Concentrator Solar Cell Technology.Dr Fetzer is manager of theMOVPE research and develop-ment group responsible for thedevelopment of metal–organicvapor phase epitaxial depositionprocesses for advanced solarcells and photonic devices. Hereceived his BS in Physics andPhD in Materials Science andEngineering from University ofUtah. As an Associate TechnicalFellow at the Boeing Companyhe has developed advancedepitaxial layers of III–Vcompound semiconductors.Before joining Spectrolab in 2001, Dr Fetzer performed researchunder Dr G. B. Stringfellow at the University of Utah exploring theuse of surfactant-mediated epitaxy to control ternary alloymicrostructure and the underlying surface physics.Spectrolab, Inc, Sylmar, California, 91342, USA174 |Energy Environ. Sci., 2009,2, 174–192This journal isªThe Royal Society of Chemistry 2009REVIEW www.rsc.org/ees| Energy & Environmental Sciencethe previous year. Ostensibly, growth in the PV industry isprojected to continue growing through 2010 including PVinstallations.Components such as modules, inverter, tracker, installationand other balance of systems (BOS) are what typically define aninstalled PV system. The burgeoning demand of global PVinstallations is driven by the factors mentioned above; however,not all solar cells produced each year have in the past beenconverted to installed PV power. The disparities between PVproduced and installed are due to the lack of more aggressivesolar Renewable Portfolio Standards, the deficiency of moremarket incentives, the lack of implementing product andbuilding regulations, and issues with the supply chain of opticalcomponents.3–7Despite this, global PV installations are rising. In2007, they rose by an average of 46% compared to 2006 witha finishing year-end total in the range of 2287–2826 MWaccording to various reports with one rendition evident inFig. 1.8–10Most of the power came from Europe, demonstratingdominance once again in this area. Over 1300 MW of this,however, was installed in Germany which is still holding a largesection of the industry’s market share for installed PV. Theglobal cumulative installed PV electricity in 2007 was over 9 GWwhich is still an insignificant amount when comparing to theestimated total power consumption in the world of 18 TW (1.8 1010kW).11,12The total cumulative power from installed, grid-tied, concentrating photovoltaics (CPV) in 2007 was over1.5 MW mostly based on single crystal silicon (Si) solar cells andmultijunction cells from III–V semiconductors.13–18Joseph Boisvert was born inMalden, Massachusetts. Hereceived his BS from theMassachusetts Institute ofTechnology in 1980 and MS andPhD degrees from the Univer-sity of Illinois at Urbana-Champaign in 1984. Dr Boisvertis presently a Senior Scientist/Engineer at Spectrolab, Inc.,a Boeing Company, where he isresponsible for developing III–Vphotodetectors and solar cells.He has 24 years of experience inthe research and development ofsolid-state photodetectors and solar cells, including device andprocess design, modeling, test and data analysis. Dr. Boisvert is anAssociate Technical Fellow of the Boeing Company.Dr Richard R. King is BoeingTechnical Fellow and PrincipalScientist responsible for Photo-voltaic Cell R&D at Spectrolab.He received his BS, MS andPhD degrees at StanfordUniversity. His photovoltaicsresearch over the last 20 yearsincludes work on III–V meta-morphic materials and devices,4-, 5-, and 6-junction cells, andminority-carrier recombinationat heterointerfaces. Dr King ledSpectrolab’s development ofhigh-efficiency III–V multi-junction cells, resulting in the first solar cells of any type to reachover 40% efficiency, and was recognized with R&D 100 awards in2001 and 2007, and a Scientific American 50 award in 2002. DrKing was inducted into the Space Technology Hall of Fame in2004, and has 11 patents and over 90 publications on photovoltaicsand device physics.Mr Hebert received his BS inMechanical Engineering and BAin Philosophy from the Univer-sity of Notre Dame, and hisMS in Mechanical Engineeringfrom Colorado State University.Mr Hebert performedmanufacturing energy efficiencyaudits at the Industrial Assess-ment Center at Colorado Statewhile performing his research onhigh speed deposition of CdTesolar cells. Mr Hebert isa Senior Staff Engineer atSpectrolab. He has nine yearsexperience of performing characterization and qualification testingon multijunction space cells and has received four Hughes Tech-nical Excellence Awards, a patent and a trade secret. Mr Hebert iscurrently leading qualification of the first generation multijunctionterrestrial cells.Dr N. H. Karam is Vice Presi-dent of Advanced TechnologyProducts and has the overallresponsibility for Boeing -Spectrolab’s internally andexternally funded R&D projects.He has over 20 years of experi-ence in materials research,photovoltaic and optoelectronicdevices, and MOCVD reactordesign. He is currently activelyinvolved in the development ofadvanced space solar cellsthrough Spectrolab’s jointlyfunded Dual Use Science &Technology program with the Air Force Research Laboratory. DrKaram and his Advanced Technology Products Team recently wonthe R&D 100 and the Scientific American 50 awards forcontributions in the field of energy generation.This journal isªThe Royal Society of Chemistry 2009Energy Environ. Sci., 2009,2, 174–192 | 175
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