Thin-Film PV Technologies III-V PV Technology Week 5.1 Arno Smets - PowerPoint PPT Presentation

Thin-Film PV Technologies III-V PV Technology Week 5.1 Arno Smets

` (Source: NASA)

III – V PV Technology

Semiconductor Materials III-V semiconductors: GaAs: GaP: InP: InAs: GaInAs: GaInP: AlGaInAs: AlGaInP:

Atomic Structure Silicon GaAs Lattice constant Lattice constant Lattice constant: 0.565 nm Lattice constant: 0.543 nm 4.42  10 22 cm -3 5.0  10 22 cm -3 Atom density: Atom density: 5.32 gcm -3 2.33 gcm -3 Density: Density:

Energy X-valley E g = 1.42 eV G -valley E L = 1.71 eV T = 300K E X = 1.90 eV L-valley E 90 = 0.34 eV E x E L E g <100> <111> Wave vector Heavy holes

Absorption coefficient Absorption coefficient, a (cm -1 ) 10 7 GaAs InP 10 6 Germanium 10 5 Silicon 10 4 10 3 10 2 10 1 10 0 200 400 600 800 1000 1200 1400 1600 1800 2000 Wavelength, l ( nm)

Charge Carrier Recombination Radiative Auger SRH

Spectral Mismatch 100 Other losses Percentage of incident 75 Relaxation light energy Below-bandgap to band 50 photons edges 25 Usable electric power 0 0 1 2 3 Bandgap (eV)

Multijunction C C V “ Excess “ Excess V energy ” energy ”

Contact= III-V Technologies AR n+-GaAs n-AllnP Top cell window/emitter n-GalnP n-GalnP Top cell base/BSF p-AlGalnP Wide-Eg tunnel junction p++-tunnel junc. n++-tunnel junc. Middle Cell Window Middle cell window/emitter n-GaAs p-GaAs Middle cell base/BSF p-GalnP p++-tunnel junc. n++-tunnel junc. buffer TC & MC crystal quality: nucleation Nucleation, buffer, n-Ge Interface control, Courtesy: Richard King Lattice-matching p-Ge substrate Spectro Labs contact

Contact= III-V Technologies AR n+-GaAs n-AllnP Top cell window/emitter n-GalnP n-GalnP Top cell base/BSF p-AlGalnP Wide-Eg tunnel junction p++-tunnel junc. n++-tunnel junc. Middle Cell Window Middle cell window/emitter n-GaAs p-GaAs Middle cell base/BSF p-GalnP p++-tunnel junc. n++-tunnel junc. buffer TC & MC crystal quality: nucleation Nucleation, buffer, n-Ge Interface control, Courtesy: Richard King Lattice-matching p-Ge substrate Spectro Labs contact

Contact= III-V Technologies AR n+-GaAs n-AllnP Top cell window/emitter n-GalnP n-GalnP Top cell base/BSF p-AlGalnP Wide-Eg tunnel junction p++-tunnel junc. n++-tunnel junc. Middle Cell Window Middle cell window/emitter n-GaAs p-GaAs Middle cell base/BSF p-GalnP p++-tunnel junc. n++-tunnel junc. buffer TC & MC crystal quality: nucleation Nucleation, buffer, n-Ge Interface control, Courtesy: Richard King Lattice-matching p-Ge substrate Spectro Labs contact

Multi-junction approach Single junctions 15 Window side 3 3 10 J (mA/cm 2 ) 2 ? 2 1 ? 1 5 ? 0 0.0 0.2 0.4 0.6 0.8 1.0 1.4 1.6 Voltage (V)

Multi-junction approach Single junctions 15 Window side 3 3 10 J (mA/cm 2 ) 2 1 2 1 2 1 5 3 0 0.0 0.2 0.4 0.6 0.8 1.0 1.4 1.6 Voltage (V)

Multi-junction approach Single junctions Multi-junctions 15 30 30 3 25 25 3 10 20 20 J (mA/cm 2 ) J (mA/cm 2 ) 2 ? 2 15 15 1 10 10 1 5 5 5 0 0 0 0.0 0.2 0.4 0.6 0.8 1.0 1.4 1.6 0.0 0.2 0.4 0.6 0.8 1.0 1.4 1.6 Voltage (V) Voltage (V)

Equivalent circuit - ideal solar cell I I D + I PH V OC,1 _

Series or parallel? I I I D I D + + I P I P J SC,1 V OC,1 H H _ _ I I I D I D + + + + I P I P V OC,2 J SC,2 H H _ _ _ _ I I I D I D + + + + I P I P J SC,3 V OC,3 H H _ _ _ _ V OC,1 V OC,2 V OC,3 J SC,1 J SC,2 J SC,3 + + + +

Series or parallel? I I I D I D + + I P I P J SC,1 V OC,1 H H _ _ I I I D I D + + + + I P I P V OC,2 J SC,2 H H _ _ _ _ I I I D I D + + + + I P I P J SC,3 V OC,3 H H _ _ _ _ V OC,1 V OC,2 V OC,3 J SC,1 J SC,2 J SC,3 + + + +

Multi-junction approach Single junctions Multi-junctions 15 30 30 3 25 25 3 10 20 20 J (mA/cm 2 ) J (mA/cm 2 ) 2 ? 2 15 15 1 10 10 1 5 5 5 0 0 0 0.0 0.2 0.4 0.6 0.8 1.0 1.4 1.6 0.0 0.2 0.4 0.6 0.8 1.0 1.4 1.6 Voltage (V) Voltage (V)

Multi-junction approach Single junctions Multi-junctions 15 30 30 3 25 25 3 3 10 20 20 J (mA/cm 2 ) J (mA/cm 2 ) 2 2 2 15 15 1 1 1 1+2+3 10 10 5 5 5 0 0 0 0.0 0.2 0.4 0.6 0.8 1.0 1.4 1.6 0.0 0.2 0.4 0.6 0.8 1.0 1.4 1.6 1.8 2.0 2.2 2.4 Voltage (V) Voltage (V)

p n Triple Junction p n p n

p p n p n n

= =

Triple Junction p p p n n n

Epitaxy of III-V Materials Crystalline growth induced by a crystalline substrate Source: http://www.photonics.ethz.ch/research/core_competences/technology/

Epitaxy of III-V Materials

Epitaxy of III-V Materials Source: http://www.photonics.ethz.ch/research/core_competences/technology/

Bandgap vs. Lattice constant 4.0 3.6 ZnS MgSe 3.2 GaN 2.8 ZnSc Bandgap (eV) AlP 2.4 CdS ZnFe GaP 2.0 AlAs BP 1.6 CdSe GaAs CdTe BAs AlSb InP 1.2 Si 0.8 InN GaSb Ge 0.4 InSb InAs 0.0 4.5 5.0 5.5 6.0 6.5 Lattice Constant (Å)

Crystal mismatch: interface defects E.F E.F. Schubert Light-Emitting Diodes (Cambridge Univ. Press) www.LightEmittingDiodes.org

Bandgap vs. Lattice constant 4.0 3.6 ZnS MgSe 3.2 GaN 2.8 ZnSc Bandgap (eV) AlP 2.4 CdS ZnFe GaP AlAs 2.0 BP 1.6 CdSe GaAs CdTe AlSb BAs InP 1.2 Si 0.8 InN GaSb Ge 0.4 InSb InAs 0.0 4.5 5.0 5.5 6.0 6.5 Lattice Constant (Å)

Spectrolab AM 0 conditions J SC = 17.76 mA/cm 2 V OC = 2.633 V FF = 0.85

EQE spectrum of multijunction cells MH Tsutagawa et al. 34 th IEEE PVSC pp. 1959 (2009)

EQE spectrum of 4-junction cells http:// www.ise.fraunhofer.de/en/press-and-media/press- releases/presseinformationen-2013/43.6-four-junction-solar-cell- under-concentrated-sunlight

Lattice Matched and Metamorphic 3-Junction Cell Cross-Section Contact AR n+-GaAs n-AllnP n-GalnP Contact AR n-GalnP n+-GaAs n-AllnP p-AlGalnP BSF n-GalnP p++-tunnel junc. GaIP top cell n++-tunnel junc. n-GalnP n-Ga(In)P window p-AlGalnP BSF n-Ga(In)As emitter Wide-bandgap tunnel junction p++-tunnel junc. n++-tunnel junc. n-Ga(In)P window p-Ga(In)As base n-Ga(In)As emitter p-GalnP BSF Ge(In)As middle cell p-Ga(In)As base p-GalnP BSF p++-tunnel junc. Tunnel junction p++-tunnel junc. n++-tunnel junc. n++-tunnel junc. Buffer region N-Ga(In)As buffer N-Ga(In)As buffer nucleation nucleation n-Ge n-Ge Courtesy: Richard King Ge bottom cell p-Ge substrate p-Ge substrate Spectro Labs contact contact

III – V PV Technology

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