Ambition for the Future of Space Components from the Viewpoint of a Researcher in the Field of Space Solar Cells Masafumi Yamaguchi

Transcription

1 Ambition for the Future of Space Components from the Viewpoint of a Researcher in the Field of Space Solar Cells Masafumi Yamaguchi Toyota Technological Institute (Nagoya, Japan)

2 Outline 1. Introduction 2. Personal R&D Profile in PV 3. Experience of Space Flight Demonstration and Space Application of Solar Cells Developed under Terrestrial (NEDO) Project 4. Future Prospects in the Field of Space Solar Cells - Seeds for Space Applications from Products Developed for Terrestrial Use - 5. Summary

3 1.Introduction

4 Invention of solar cells at the Bell Telephone Labs. (1954)

5 The first Si space solar cells for the Vanguard 1 (1958)

6 Contribution of the space solar cells to the Space Station from the Vanguard 1.

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8 Schematic cross section of Si space solar cells developed by Sharp Co.

9 2. Personal R&D Profile in PV

10 Personal R&D Profile in PV (1) Year R&D projects Radiation damage to Si devices including solar cells Development of space solar cells (InP, AlGaAs/GaAs 2- junction and GaAson-Si cells) Results Impurity effects of defect generation in Si 1984: Discovery of minoritycarrier injection-enhanced annealing of defects in InP 1987: Proposal of DHstructure tunnel junction for MJ solar cells 1987: 20.2% AlGaAs /GaAs 2-junction cell 1989: 20% GaAs-on-Si cells 1990: Launching of MUSES- A using InP cells

11 Year Personal R&D Profile in PV (2) R&D projects Development of super -high-efficiency MJ solar cells (NEDO, MITI) Fundamental studies of high-efficiency MJ and other solar cells, and materials (TTI) Development of super -high-efficiency concentrator MJ cells and modules (NEDO, METI) Results 1997:33.3% InGaP/GaAs /InGaAs 3-junction cell 1996: Proposal of anomalous degradation mechanism of Si space cells 1997: Discovery of minoritycarrier injection-enhanced defects annealing in InGaP 2003: 27% large-area (7,000cm 2 ) concentrator 3-junction cell modules 2004: 39.2% InGaP/InGaAs /Ge concentrator 3-J cell

12 Discovery of Superior radiation-resistance of InP solar cells (1984), under dark and light illumination conditions compared to Si and GaAs cells.

13 DLTS analysis for minority-carrier injection phenomena of radiation-induced defects in InP materials and solar cells.

14 Temperature dependence of annealing rates of major radiation-induced defects in InP and GaAs under thermal and injection annealing.

15 Technology transfer of InP solar cell fabrication technologies from my previous NTT lab. to the Nippon Mining Corp. First InP space solar cells (1x2cm 2, 2x2cm 2 ), made using the thermal diffusion method, by the Nippon Mining Corp. for Japanese scientific satellite MUSES-A.

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17 First space flight of InP space solar cells using Lunar Mission Japanese scientific satellite MUSES-A (1990).

18 1.1eV (Si) (a) 2-junction cell (b) 3-junction cell Potential of high-efficiency for monolithic cascade III-V/Si multi-junction solar cells

19 Reduction in dislocation density (etch-pit density) in GaAs films on Si due to thermal cycle annealing (TCA).

20 Transmission electron microscope image of GaAs film on Si thermal cycle annealed (TCA).

21 Mechanisms for dislocation motion in III-V compound film on Si substrate Hetero-epitaxial Film Propagation Deflection +Propagation Deflection to edge Annihilation Combination +Re-emission Substrate

22 p + -AlG aas n + -AlG aas /n + -G a A s SL n + -InG aas /n + -G a A s SLS p + -G aas n-g aas n + -G aas SiS ub. A R (S i N ) 3 4 n + -G aas The structure and I-V curve (AM0) of a high-efficiency GaAs-on-Si solar cell.

23 Number Average AM0 Efficiency 16.86% AM0 Efficiency (%) AM0 efficiency distribution of 48 2cmx2cm GaAs-on-Si solar cells with 50μm and 100μm thick cover glass.

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25 Remaining Factor of Pmax (%) GaAs-on-Si Cell (50um Cover Glass) GaAs-on-Si Cell (100um Cover Glass) 50um-thick Si Cell (50um Cover Glass) GaAs-on-GaAs Bulk Cell (50um Cover Glass) 100um-thick Si Cell (50um Cover Glass) 200um-thick Si Cell (50um Cover Glass) Various space solar cells evaluated using ETS-VI Remaining factor of maximum power for GaAs-on-Si cells after 94 days from launching in comparison with those for LPE-grown GaAs-on-GaAs cells and thin Si cells.

26 1.5 In G a P AM 1.5 Spectrum Spectral Irradiance [k W / m 2. μm ] GaAs Ge W a v e le n g th (μ m ) AM 1.5 Spectrum and W ide B and Spectral R esponse by M ulti-junction Solar C ell Beginning of MJ solar cell studies (1982) Proposing and starting NEDO R&D project (1990): MJ Proposing and modifying NEDO R&D project (2001): Conc. MJ

27 Bandgap Energy of Bottom Cell (ev ) GaAs AM1.5, 1-sun, T=300K In0.5Ga0.5P 2Term inal Top Cell Tunnel J. Bottom C ell N P N P P++ N Bandgap Energy of Top C ell (ev) Potential of high-efficiency 2-junction cell

28 CURRENT DENSITY (A/cm 2 ) InGaP TJ AlInP/InGaP DH without AlInP VOLTAGE (V) Changes in I-V curves of the InGaP tunnel diodes by introducing the DH structure.

29 2 Tunnel peak current density(a/cm ) X=0 X=0.6 X=0.9 top cell PAlxGa1-XAs p ++ GaAs n ++ GaAs nalxga1-xas ngaas sub bottom cell Annealing temperature dependence of tunnel peak current densities for double hetero structure tunnel diodes. X is the Al mole fraction in Al x Ga 1-x As barrier layers.

30 Mechanism of Impurity Diffusion in the Tunnel Junction

31 Voc = 2.1V Isc = 13.8 ma/cm 2 FF = 0.70 Eff. = 20.2% A structure and I-V curve of a high-efficiency AlGaAs/GaAs 2-junction cell (1987)

32 3. Experience of Space Flight Demonstration and Space Application of Solar Cells Developed under Terrestrial (NEDO) Project

33 80 70 InGaP Eg=1.88eV Top cell Tunnel Junction AR MgF2/ZnS Au/Au-Ge/Ni/Au (Front contact) n + GaAs 0.30 µm <5x10 18 cm -3 : Si n + AlInP : 0.03 µm<2x10 18 cm -3 : Si n + InGaP : 0.05 µm. 2x10 18 cm -3 : Si p InGaP : 0.55 µm.1.5x10 17 cm -3 : Zn p + InGaP : 0.03 µm.2x10 18 cm -3 : Zn p + AlInP : 0.03 µm.<5x10 17 cm -3 : Zn p + InGaP : µm.8.0x10 18 cm -3 : Zn n + InGaP : µm.1x10 19 cm -3 : Si Current [ma] AM0, 28.1 C Cel: 2cm x 2cm Isc: 67.4 [ma] Voc: 2451 [mv] FF: 88.1 [%] η: 26.9 [%] n + AlInP : 0.05 µm.1x10 19 cm -3 : Si 0 GaAs Eg=1.43 ev Bottom Cell n + GaAs : 0.1 µm.2x10 18 cm -3 : Si P GaAs : 3.0 µm.1x10 17 cm -3 : Zn p + InGaP : 0.1 µm.2x10 18 cm -3 : Zn Voltage [mv] p + GaAs : 0.3 µm.7x10 18 cm -3 : Zn p + GaAs : Subs.<1x10 19 cm -3 : Zn Au (Back contact) The structure and I-V curve of a high-efficiency InGaP/GaAs 2-junction solar cell under AM0 illumination: Previous world-record efficiency at AM0.

34 Recovery of radiation-induced defects in InGaP cells Recovery of InGaP cells is due to the anneal-out of some of the radiation-induced defects during device operation which has been confirmed by DLTS. This unique property of radiation damage recovery in InGaP cells demonstrates InGaP materials and devices have great potential for space applications. Power Ratio P I /P MeV e/cm 2 Injection Current: 100mA/cm 2 75 C Injection Time (min) 50 C 25 C The maximum power recovery of the single-junction InGaP cell due to current injection at various temperatures.

35 p-ingap 0 min emission rate=1005 s -1 Injection anneals 100mA/cm 2 at 25 o C 8 7 H2 (0.50 ev) (a) Single carrier Pulse VR = 3V Pluse Amplitude = 0V DLTS Signal (a.u.) 0.5 min 5 min 10 min 20 min N T ( x cm -3 ) (b) Double carrier pulse VR = 3V Ist pulse Amplitude = 0V 2nd pulse Amplitude = -2V (80 ma cm -2 ) Period width = 20 ms pulse width = 3 µ sec Temperature (K) Temperature (K) Minority-carrier injection enhanced annealing of major radiation-induced defect H2 in InGaP and evidence of recombination center confirmed by the DLTS method.

36 Space flight demonstration of InGaP/GaAs 2-junction cells by the Mission Demonstration test Satellite-1 (MDS-1, 2002)

37 InGaP/GaAs Tandem Cell 1.00 Remaining Factor Tandem-100 (Isc) Tandem-500 (Isc) Tandem-100 (Voc) Tandem-500 (Voc) MET (days after launch) Superior radiation-tolerance of InGaP/GaAs 2-junction cells confirmed by the Mission Demonstration test Satellite-1 (MDS-1, )

38 0ptical loss reduction (AR) Cell interconnection loss reduction (Tunnel junction) Contact loss reduction Surface, interface recombination loss reduction Bulk recombination loss reduction Lattice matching High quality ep. Carrier confinement Photon confinement Current matching Material selection Device structure Key issues for high efficiency MJ cells

39 Band Diagram of DH Tunnel Junction Eg2 Eg1>Eg2 Eg1 Top Cell Tunnel Junction Middle Cell

40 Structure of Triple-Junction (3J) Cell AR Coating n + (In)GaAs n + AlInP [Si] n + InGaP [Si] p InGaP [Zn] p AlInP [Zn] p ++ AlGaAs [C] n ++ InGaP [Si] n + AlInP [Si] n + (In)GaAs [Si] p (In)GaAs [Zn] p + InGaP [Zn] p ++ AlGaAs [C] n ++ InGaP [Si] n + n + (In)GaAs [Si] GaAs : 0.1µm n p Ge Substrate Front Contact InGaP Top Cell Tunnel Junction InGaAs Middle Cell Tunnel Junction Buffer Layer Ge Bottom Cell Back Contact 2 ) Current Density (A/cm AM1.5G, 1cm 2 Jsc: ma/cm 2 Voc: V FF: 85.8 % Eff.: 31.7 % Voltage (V) Characteristics of 3J Cell (x=0.01) Quantum Efficiency (%) In 0.49 Ga 0.51 P In0.01Ga0.99As Wavelength (nm) Ge A structure of a high efficiency InGaP/GaAs/Ge 3-junction cell fabricated on a Ge substrate.

41 N Contact ARC P Contact n+-gaas n-ingap p-ingap n-gaas p-gaas n-gaas n-ge p-ge Substrate GaAs Cap Layer InGaP Top Cell Tunnel Junction GaAs Middle Cell Tunnel Junction Buffer Layer Ge Bottom Cell InGaP/GaAs/Ge 3-junction space solar cell made by Sharp Co. (Technology transfer from terrestrial use to space use)

42 80 CURRENT (ma) AM0, 135.5mW/cm 2, 28 Size: 2x2 cm 2 Voc: 2567 mv Jsc: 17.9 ma/cm 2 FF: Eff: 29.2 % VOLTAGE (mv) Current-voltage of InGaP/GaAs/Ge 3-junction space solar cell made by Sharp Co.

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44 4. Future Prospects in the Field of Space Solar Cells - Seeds for Space Applications from Products Developed for Terrestrial Use -

45 Terrestrial use AM0 Efficiency (%) J 2-J 2-J Conc. InP Conc. GaAs GaAs-on-Si Si InP a-si CIGS AM1.5 Efficiency (%) Space use Correlation between AM0 and AM1.5 Efficiencies for Various Solar Cells

46 WBGU s World Energy Vision ,600 1,400 WBGU: German Advisory Council on Global Change Geothermal Other REs Solar heat Primary Energy Supply [EJ/Y] 1,200 1, YEAR Solar electricity Wind Biomass adv Biomass trad Hydro-PW Nuclear PW Gas Coal 0 Oil

47 Cumulated Cumulated(20%Growth) Cumulated(30%Growth) NSS Milestone Scenario 1 Scenario Cumulative Installed Capacity (GW) Year Cumulated installed capacity of PV systems in Japan by year.

48 Module (Cell) efficiency target (%) in Japanese PV2030 road map. CELL TYPE Thin-Bulk Multi-c-Si 16 (20) 19 (25) 22 (25) Thin-Film Si 12 (15) 14 (18) 18 (20) CIS 13 (19) 18 (25) 22 (25) Super-High η 28 (40) 35 (45) 40 (50) Dye-sensitized 6 (10) 10 (15) 15 (18)

49 Si cells GaAs cells MJ cells Future cells 50 Production-level AM0 Efficiency (%) Year Toward 50% Efficiency for Future Space Solar Cells

50 High Efficiency InGaP/InGaAs/Ge 3-Junction Solar Cell and Its Concentrator Application

51 Concentration Ratio Dependence of High Efficiency InGaP/InGaAs/Ge 3-Junction Solar Cells

52 CURRENT (A) sun Voc: 3.12 V Isc: 3.46 A FF: 0.88 Eff: 38.9% 38.9% at 498-suns AM1.5 (39.2% at 200-suns AM1.5) VOLTAGE ('V) Most Recent Results: I-V Curve of a High Efficiency InGaP/InGaAs/Ge 3-Junction Solar Cell under 498-suns AM1.5

53 50 Multi-Junction 40 New Mater. Efficiency (%) Cryst. Si Thin-Film Si Dye-Sensitized 10 CIS a-si Organic Year Future Predictions of Solar Cell Efficiencies (Original idea by Prof. A. Goetzberger. Modified by M. Yamaguchi)

54 1.5 Current (A) Irradiance (DNI): 751 W/m 2 Ambient Temperature: 35.0 C Wind Velocity: 0.5 m/s Area: 196 cm2 Isc: A Voc: V FF: η: 27.0 % Voltage (V) Outdoor evaluation of I-V of large-area (7,000cm 2 ) concentrator InGaP/InGaAs/Ge 3-junction cell module (Including loss in concentrator optics and temperature rise)

55 :Si crystal 2:thin-film 3:concentrator Electricity Cost (Yen/kWh) Summary 1 of estimated cost for Scenario of electricity cost reduction by the concentrator PV systems vs developing concentrator 2025 solar 2030 cells. concentration ratio. Year Scenario of electricity cost reduction by developing concentrator solar cells.

56 Past Future 1000 Specifuc Power (W/kg) Year Specific power of space solar cell arrays Toward light weight (1kW/kg)

57 MJ/Ge(5.5mil)/rigid MJ/Ge(5.5mil)/light MJ/Si(2mil)/light Thin-Film/Poly(1.5mil)/light Thin/rigid MJ/Ge(2mil)/light Thin-Film/SS(1mil)/light Specific Power (W/kg) AM0 Efficiency (%) Toward Developing Light Weight Space Solar Cells

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62 Annealing rate (s -1 ) 1.0E E E E E /T (K -1 ) Minority-carrier injection annealing of radiation damage to CuInGaSe 2 cells

63 Large CIS Cell 1.00 Remaining Factor LA CIS-100 (Isc) LA CIS-500 (Isc) LA CIS-100 (Voc) LA CIS-500 (Voc) MET (days after launch) Superior radiation-tolerance of CuInGaSe 2 solar cells confirmed by the Mission Demonstration test Satellite-1 (MDS-1, )

64 5. SUMMARY (1)Luckily, I have discovered superior radiationresistance of InP and solar cells. We have developed high-efficiency InP and GaAs-on-Si solar cells and performed a space flight demonstration. (2)We have also developed a break-through technology (DH-structure tunnel junction) for multi-junction solar cells. (3) Based on our research results, the NEDO R&D project for high-efficiency multi-junction solar cells for terrestrial application has been started in Japan.

65 5. SUMMARY-Continued (4) In that project, high-efficiency InGaP/GaAs 2- junction and InGaP/InGaAs/Ge 3-junction cells with AM0 efficiencies of 26.9% and 29.2%, respectively, have been developed and their technologies have been transferred for space use. (5) We have sown seeds for high-efficiency and lowcost multi-junction concentrator solar cells and modules, flexible and high-efficiency thin multijunction cells, and radiation-resistant thin-film CuInGaSe cells for space applications. (6) However, I really expect that results from R&D on materials, devices, components and systems for space use will be transferred to terrestrial use in the similar way with the Apollo Project in USA.

66 Terrestrial use Space use! 50 AM0 Efficiency (%) J 2-J 2-J Conc. InP Conc. GaAs GaAs-on-Si Si InP a-si CIGS AM1.5 Efficiency (%) Correlation between AM0 and AM1.5 Efficiencies for Various Solar Cells

67 Be Ambitious! Let new ideas bring your wishes and

68 Thank you very much!