Multijunction Photov

Technologies for H

Performance Concent

Robert D. McConnell & Martha Sy

High Performance Photovoltaic Pro

National Center for Photovoltaics

National Renewable Energy Labora

NREL/PR-520-39866Presented at the 2006 IEEE 4th World Conference on Photovoltaic Energy Conversion (WCMay 7-12, 2006 in Waikoloa, Hawaii.
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• Systems D

• Technical 

Opportunit

• Stage Gat• Solar Advi

Cell & S

Integra

Cells 

Markets

Materials

III-V High 

Performance 

Systems

Device Design

Spectrum

AR Coating

Rece

High Performance Concentrator 

Market Incentives

Standards

Applications

Large utility plantsRooftopsDefense

Co
Efficiency Impact on Levelized Cost of E

System Size MW 10 12.5 Module Price $/Wdc 4.13 3 

Cell Efficiency % 26 

(Si)

32 (III-V)

Module Size kWpdc 40 50 

Module Efficiency % 20 25 Installed System Price

$/Wdc 5.95 4.3 

Levelized Cost of Energy (LCOE)

$/kWhac 0.15-0.27 0.10-0.1

Reference: DOE MYPP 2007-2011: from Table 
Subcontractor Concentrator Cells Project Title

Spectrolab, Inc. Ultra-High-Efficiency Multijunction Cell and Receiver M

California 

Institute of 

Technology

Four Junction Solar Cell with 40% Target Efficiency Fa

by Wafer Bonding and Layer Transfer

University of 

Delaware

Novel High Efficiency Photovoltaic Devices Based on tMaterial System

Ohio State 

University

Optimized III-V Multijunction Solar Cells on Patterned aSubstrates

University of 

Delaware

Theoretical and Experimental Investigation of Approac>50% Efficient Solar Cells

High Performance Concentra

Subcontracts (2004–200
Subcontractor Concentrator Systems Project Title

Amonix, Inc. Design and Demonstration of >33% Efficient Hig

Concentration Module using >40% III-V MultijunDevices

Concentrating Technologies, 

LLC

A Scaleable Reflective Optics High Concentration PV S

SunPower

Corporation/JX 

Crystals

Low Concentration PV System Prototype Assessment oMirror Module with SunPower’s 20% Efficient A-300 So

Arizona State 

University

Development of IEC Design Qualification Standard for 

Concentrator PV Modules

JX Crystals, Inc. Toward 40% Efficient Hybrid Multijunction III-V Terrestr

Concentrator Cells

High Performance Concentrator P

(2004–2007) cont.
• Broader Impact:

• Pushing III-V multijunction cells to ever 

higher efficiency lowers balance-of-module and balance-of-system costs, making concentrator PV one of the most costeffective renewable electricity sources. 

• Long-term receiver reliability studies lead to 

widespread implementation of and confidence in concentrating PV. 

• Approach:

1. High-efficiency GaInP/GaInAs/Ge triplejunction concentrator solar cells2. Metamorphic, lattice-matched, and mechanically stacked solar cells

3. Analytical modeling and long-term 

experimental evaluation of different receiver designs

• Significant Results:• 39.0% (lattice matched) and 38.8

concentrator cells 

• One year of receiver tests @ 220 

performance.

• Research Objectives:

This program aims to develop ultra-highefficiency triple-junction solar cells and to demonstrate a working robust receiver packages.

(a) 

• Graphic:

(a) Type 1 cell assembly develo

focus systems such as Fresnel l(b) Type 2 cell assembly for densuch as reflecting parabolic dish 

Ultra-High-Efficiency Solar Cell and Receiv

PI: Richard R. King & Raed A. Sherif, Spect
Title: Four-Junction Solar Cell with 40% Target Efficien

by Wafer Bonding and Layer Transfer

PI: Harry Atwater, California Institute of Technology

Demonstrate a 40%-efficient, 1-cm2 solar cell 

optimized for terrestrial application using a nonlattice-matched tandem heterojunction fabricated by wafer bonding and layer transfer fabrication.

1. Wafer-scale synthesis of InP/Si, Ge/Si and 

GaAs/Si transferred epitaxial template films by layer transfer fabrication. 

2. Grow high-quality epitaxial compound 

semiconductor 2-junction subcells and doubleheterostructures in (InGaP/GaAs/Ge/Si and InGaAsP/InGaAs/InP/Si) on transferred epitaxial template layers. 

Active ongoing research projects with Spectrolab is a significant component of this program; Spectrolab is fabricating MOCVD double-heterostructures and pn junction solar cells on the epitaxial templates from Caltech.

• Wafer-scale layer transfer of G

achieved at the 50-mm wafer 

• Less than 1 nm roughness an

resistance for Ge/Si and InP/S

• Fabricated active GaInP and 

with about 107/cm2 defects on 

• Research Objective:• Approach:• Industry Impact:

• Significant Results:

• Graphics: 

Above: Schematic of 4-junction solar cell with bonded layers. Above right: Bonded InP/Si film on 50 mm wafer

GaAshν = 1.42eV

InGaAsPhν = 1.05eV

InGaAshν = 0.72eV

Si

Substrate

GaInP2hν = 1.9eV

InP bonded toSi substrate

GaAs bonded layer
Novel High-Efficiency Devices Based on the InGaN Mate

PI: Christiana Honsberg, University of Delaware

To demonstrate high-performance tandem solar cells based on the InGaN material system.

• GaN solar cells with external Q

when measured through metal 

• InGaN solar cells with 7% 

In shows 2V Voc, dominated by radiative defect channel 

• Growth of InN

demonstrated on Ge,with AlN or Al as abuffer

• Research Objective:• Approach:• Industry Impact:

• Significant Results:

• Graphics:

• High bandgap: Develop GaN and In-lean 

InGaN p-i-n and quantum well solar cells.

• Low bandgap: Develop understanding of 

In-rich InGaN materials grown on Ge.

Emission from 

• InGaN grown on Ge and Si could offer a 

continuum of bandgaps over the solar 

spectrum, offering path to high-efficiency, 

low-cost tandem solar cell in one alloy.
• Industrial and Broader Impact:

- Combining high-performance III-V PV concentrators with low-cost Si substrates exploits advantages of both to achieve $/W goals- Identical materials science has already achieved communication-band infrared and visible laser diodes on Si; combined with > 2 V cells on Si, this opens door to selfpowered systems on Si chips

• Research Objectives: • Significant Resu

Develop and demonstrate the use of novel 3-D substrate engineering in Si and Ge to achieve spectrum-optimized Egprofiles leading to > 40% III-V multijunction concentrators on Si or Ge

• Graphics: Below: X

grown and fabricated on 

GaAs grown on perfectl

Optimized III-V Multijunction Concentrator Solar Cells on PatterSubstratesPI: Steven A. Ringel, Ohio State University (MIT subtier contrac

InGaP GaAs 

GradeGe

tun

I μm

• Approach:

1. Grow, characterize, and optimize InGaAs/Ge and InGaAs/SiGe/Si substrates that incorporate both lattice grading and patterning to achieve ideal and tunable substrate lattice constants suitable for super-efficient III-V concentrators.

2. Grow and fabricate solar spectrum-optimized 

InGaP/InGaAs double- and InGaP/GaAs/SiGe triplejunction concentrators on 3-D engineered Si and Ge wafers.

3. Compare lattice-matched and lattice-mismatched III-V 

cells on engineered substrates.

• First III-V dual-junction c• First “tuned” lattice cons

growth on Si. Achieved 

• Optimization of the uppe

Ge/SiGe/Si substrate dis6x105 cm-2

• Avoided all mismatch-re

dislocations and anti-pha
Design and Demonstration of a Greater than 33% Efficient 

High-Concentration Module Using >40% III-V Multi-junction DevPI: Kenneth Stone, Amonix Inc.

To design and fabricate a module that will use >40%-efficient multijunction solar cells. It is envisioned that such a module will be 33% efficient.

1. Design packing for the Ge substrate based 

multijunction solar cells. 

2. Test packaged cells under a Fresnel lens.3. Characterize different cells / package / lens 

configuration.

4. Design and construct 33%-efficient modules, 

to be tested on-sun, not in the laboratory.

The success commercialization of systensexceeding 33% will redefine the solar energy market—extremely tough competition for any other technology in concentrators or flat-plate or in the foreseeable future of photovoltaicsParadigm shift in installed system cost – $3/W is 

imminent—leap into the utility market.

• Solar cell integration sign

CTEs, handling sensitiviti

• The optics of a Fresnel le

very different from laboratchromatic aberration, lens 

must be matched to multij

•Identified top cell as limiting aspect of curr•Redesigned optics recell efficiency at oper

• Research Objective:• Approach:• Industry Impact:

• Significant Results:

• Graphics: Amonix 35 k
Toward 40% Hybrid Multi-Junction III-V Terrestrial Concentrato

PI: Lewis Fraas; JX Crystals Inc.

To demonstrate 40%-efficient hybrid InGaP/GaAs-GaSb multijunction cells in a 33%-efficient Cassegrainian PV concentrator panel.

• Fabricated and tested all com

modules including IR cell andichroic secondary mirror, prsinks and 25 cm x 25 cm mo

• Measured efficiency sum of 

temperature

• Research Objective:• Approach:

• Industry Impact:

• Significant Results:

• Graphics: 

GaSb IR Cell

InGaP/GaAs DJ Cell

Cassegrainwith dichroicsecondary

TODAY: 15%SiliconPlanar Stationary

FUTURE: 33%CassegrainModule

Module Cost $3.20 / W $0.75 / WTracker Cost 0 $0.25 / WInstallation Cost $1.50 / W $0.75 / WTotal Cost per W $5.50 / W $2.10KWh per kW per year 2000 2600Cost per AkWh(A=annual)

$2.75 per AkWh $0.80 per AkWh

Cents per kWh (10 year) 27.5 cents

per kWh

8 centsper kWh

3 Casseg
A Scaleable Reflective Optics High-Concentration PV System

PI: Stephen Kusek; Concentrating Technologies, LLC

To demonstrate a 33% reflective-optics concentrator module using passively cooled Spectrolab triple-junction cells at 500x.

Current single-axis tracking flat-plate silicon systems are over $6/watt installedNear-term low-megawatt MicroDish production can yield installed costs below $3/wattSystem architecture is versatile and allows nextgeneration HCPV cell as a “drop in” replacement or upgrade

• Spectrolab triple-junction pow

operation for over one year w

• More than 14 W/cm2 from the • 500x passive cooling with cell 

flat-plate norms

• Research Objective:

• Approach:

• Industry Impact:

• Significant Results:

• Graphics: 

Prototype 1-kW MicroDish system at the Arizona Public Service Solar Technology and Research (STAR) facility

2.

43at 

202020
Low-Concentration Flat-Plate Module Using High-Efficiency Sil

PIs: Richard Swanson, SunPower Corp; Lewis Fraas, JX Crysta

Opportunity: The demand for solar photovoltaic cells and modules has far outstripped PV cell supply.Solution: JX Crystals Inc. has a 3-sun mirror module design that uses 1/3 the cells to triple module production at a lower cost.

• Research Objective:

• Approach:

• Industry Impact:

• Significant Results:

• Graphics: 

1. Cut standard A300 Si cells into thirds.2. Add aluminum sheet heat spreader to back of standard flat-plate laminant. 3. Add linear mirror array on front of panel. 

Two 3-sun JXC modules and one Sharp module on 2-axis tracker yielding results shown above.

100 kW contracted for demonstration project in Shanghai 
Development of IEC Design Qualification Standard for CPV Mo

PI: Liang Ji, Underwriters Laboratories Inc.

To develop, coordinate, and publish an IEC standard for the design qualification of concentrator photovoltaic (CPV) modules

1. Contact CPV users and manufacturers to 

identify the CPV module qualification requirements.

2. Work with IEC/TC82/WG7 committee to 

improve draft versions.

3. Validate the new procedures agreed by WG7.4. Submit the draft standard to IEC for official 

circulation, comments, and voting.

Both performance and safety design qualification standards for the flat-plate PV modules have already been developed and extensively used by the industry. One potential approach to reduce the cost of solar electricity is the use of CPV modules. The performance design qualification standard development undertaken in this work would benefit the industry to introduce reliable CPV products in the worldwide marketplace.

• Submitt

internat

• Research Objective:

• Approach:• Industry Impact:

Signifi

Table of Contents1 Scope and object2 Normative references3 Terms and definitions4 Sampling5 Marking6 Testing7 Pass criteria8 Report9 Modifications10 Test procedures10.1 Visual inspection10.2 Electrical performance measureme10.3 Ground path continuity test10.4 Electrical insulation test10.5 Wet insulation test10.6 Thermal cycling test10.7 Damp heat test10.8 Humidity freeze test10.10 Water spray test10.11 Bypass diode thermal test10.12 Robustness of terminations test10.13 Mechanical load test10.14 Off-axis beam damage test10.15 Ultra-violet conditioning test10.16 Outdoor exposure test10.17 Hot-spot endurance test
High-Efficiency Concentr

• High-efficiency solar cell 

concentrator technologies are finally entering world markets

• Two companies with welldeveloped products, Amonix 

and Solar Systems, expect to install a total of 15 to 20 MW in 2006

• Many new companies are 

developing a variety of concentrator concepts 

• Next step is incorporating 

ultra- high-efficiency (>37%) cells

Amonix—

Solar Sy
Acknowledgemen

• DOE Solar Energy Technologies Prog

funding and support of these projects

• NREL’s Solar Energy Technologies P

(Roland Hulstrom) and National CentPhotovoltaics (Kaz) for their support oPerformance PV Project

• The principal investigators and their te

developing and providing their results presentation
Investigation of Approaches to >50% Solar Cells

PI: Christiana Honsberg, University of Delaware

Analyze advanced solar cell efficiency approaches, including realistic loss mechanisms, to determine realistic solar designs >50% efficiency.

• Demonstrated that proposed m

be grouped into 5 general class

• Developed models for band str

quantum dot solar cells.

• Identified two non-idealities to b

level solar cells: valence band o

• Identified material systems that 

multiple-energy-level solar cell. 

• Research Objective:• Approach:• Industry Impact:

• Significant Results:

• Graphics: 

• Develop band-structure 

models for spherical quantum dot solar cells.

• Determine design rules for 

material selection of quantum dot multipleenergy-level solar cells.

• Calculate impact of doping 

on QD energy levels.

Example ideaInAs0.68

P0.32/G

• Identification of design rules and material 

systems allows practical implementation of quantum dot solar cells.

• QD solar cells give efficiency of 3-junction 

tandem with two materials.
Quantum Dot Solar Cells

PI: Arthur J. Nozik, NREL (Collaborative Project with Office of Science/BES/Chemical Sciences)

To demonstrate multiple electron-hole pair (exciton) generation from single photons in quantum dots (QDs) and apply this effect to QD solar cells to produce greatly enhanced photocurrent and conversion efficiency

Ultra-high conversion efficiency in 3rd-generation 

solar cells will significantly reduce the cost of PV power.

• Research Objective:

•Approach: 

• Industry Impact:

• Significant Results:

• Graphics: 300

250200

Quantum Yield (%) 150

(b)

Quantum yield vs. photon energfor PbSe and PbS QDs of differdiameters).(Published in: NanoLetters, 5, 5

• Synthesize QDs that are expected to show greatly 

enhanced multiple exciton generation (MEG).

• Measure MEG using fs transient absorption 

spectroscopy.

• Develop and characterize nanocrystalline solar 

cells sensitized with QDs exhibiting efficient MEG and greater photocurrent.

• Model performance of QD solar cells showing 

efficient MEG.

1. Quantum yields of up to 300% have been measured in PbSe and energies 4 times the QD bandgap2. The enhanced performance ansolar cells based on MEG have b

Quantum Yield
High-Efficiency Multijunction Solar Cells 

PI: Sarah Kurtz, National Renewable Energy Laboratory

Create high-efficiency concentrator cells for low-cost terrestrial photovoltaic applications

1. Lattice-matched multijunction. 

Develop new 1-eV material: GaInNAs. 

2. Lattice-mismatched multijunction. 

Grow lattice-matched GaInP and GaAs cells first, then mismatched GaInAscell. Processing requires inversion and substrate removal.

3. Multijunction on silicon. 

Active Si junction with III-V top cell. Results presented in Paris & Orlando

Once high-efficiency cells are developed, NREL will work with companies to implement these in concentrator systems. NREL also supports industry with a range of projects, studying the effects of changing spectrum on multijunction device design and performance.

• Higher GaInNAs photocurrents obtai• 37.9% efficiency for early prototype o

GaInP/GaAs/GaInAs device, setting 

• Research Objective:• Approach:

• Industry Impact:

• Significant Results:

• Graphics: 

1.00.80.60.40.20.0

Internal QE

1.1 1.2 1.3 1.4 1.5

Energy (eV)

 GaAs Eg=1.28 eV

W=0.66 μm

 Eg=1.28 eV

W=2.7 μm

 Eg=1.15 eV

W=2.3 μm

GaNAs GaAs GaNAs

E

GaInAs bot. cell

Grade

GaAs middle cell

GaInP top cell

Substrate

Growth Final cell

GaInAs bot. cell

Grade

GaAs middle cell

GaInP top cell

Metal Patent by M. Wanlass