Optoelectronics: Is there anything it cannot do; Can opto-electronics provide the motive power for future vehicles?

Transcription

1 Optoelectronics: Is there anything it cannot do; Can opto-electronics provide the motive power for future vehicles? CREOL Industrial Affiliates Symposium Orlando, Florida Mar. 11, 2016 Eli Yablonovitch Electrical Engineering and Computer Sciences Dept., Univ. of California, & Lawrence Berkeley Laboratory Berkeley, CA

2 GaAs solar cells are the preferred technology, where cost is no objection: Space

3 The Epitaxial Liftoff Process:

4

5 Courtesy of Alta Devices, Inc.

6 Li Hejun

7 30 29 Alta Devices record, 28.8% Efficiency (%) sun, single junction, solar cell efficiency record: Year

8 1.15 Open Circuit voltage V OC (Volts) Alta Devices record cell, volts Open Circuit voltage for record efficiency cells: Year

9 efficiency % 33.5% new physics Shockley Queisser limit (single junction) high performing cells normal solar cells ~25% 0%

10 h h h 25.1% efficiency h + e - h h g h h h g 28.8% efficiency e - h +

11 What if the material is not ideal, and the electrons and holes are lost to heat before they can luminesce? qv oc = qv oc-ideal kt ln{ ext } The external Only external Luminescence can balance the incoming radiation. fluorescence yield ext is what matters!

12 Efficiency vs. Rear Reflectivity, Cell Efficiency (%) % 32.2% 31.9% Reflectivity GaAs 3 m 90% Rear Reflectivity Is Not Enough! Voc (Volts) Reflectivity Jsc (ma/cm 2 ) Reflectivity

13 1 sun results from Alta Devices, Inc. Expected to reach 29.8% single junction, and 34% dual junction, eventually.

14 Counter-Intuitively, to approach the Shockley-Queisser Limit, you need to have good external fluorescence yield ext!! Internal Fluorescence Yield int >> 90% Rear reflectivity >> 90% Both needed for good ext

15 For solar cells at 25%, good electron-hole transport is already a given. Further improvements of efficiency above 25% are all about the photon management! A good solar cell has to be a good LED! Counter-intuitively: 1. Thin-film cells are more efficient than the best wafer cells. 2. Solar cells perform best when there is maximum external fluorescence yield ext. Miller et al, IEEE J. Photovoltaics, vol. 2, pp (2012)

16 Dual Junction Series-Connected Tandem Solar Cell Ga 0.5 In 0.5 P V OC =1.5V Solar Cell Tunnel Contact GaAs V OC =1.1V Solar Cell h h n-al 0.5 In 0.5 P E g ~2.35eV n-ga 0.5 In 0.5 P E g ~1.8eV p-ga 0.5 In 0.5 P E g ~1.8eV p + -Al 0.5 In 0.5 P E g ~2.35eV n + -Al 0.5 In 0.5 P E g ~2.35eV n-al 0.5 In 0.5 P n-gaas E g =1.4eV p-gaas E g =1.4eV p-al 0.2 Ga 0.8 As Ga 0.5 In 0.5 P V OC =1.5V Solar Cell Tunnel Contact GaAs V OC =1.1V Solar Cell All Lattice-Matched ~34% efficiency should be possible.

17 Dual-junction 1 sun results from Alta Devices, Inc. ALTA has demonstrated >31.5% efficiency in the same system. Expected to reach 34% dual junction, eventually.

18 Friday Saturday After spending ~10 11 Euros, Germany has installed 40GW of panels, but receives only 7% of its electricity from solar

19 What is happening in the solar economy? c-si ~ 15%-23% in production 90% market share 70GW/year annual world-wide production capacity World-wide demand ~50GW/year Oversupply! The current world price has settled at $ /Watt 2 TeraWatt can be built out in 30 years, requiring no additional capacity. To justify additional production capacity New and different application markets are needed.

20 What is Thermo-PhotoVoltaics? x 10 7 Blackbody Power Spectrum Power [Watts/cm 2 /ev] wasted energy h < 0.95eV wasted energy h < 0.8eV Photon Energy [ev] 1 1.2

21 Thermo-PhotoVoltaic Hybrid Car: Only ~20% efficiency 1997 Proceedings Future Transportation Technology Conference, Christ, S. and Seal, M., "Viking 29 A Thermophotovoltaic Hybrid Vehicle Designed and Built at Western Washington University," SAE Technical Paper , 1997, doi: /

22 Recycle the Infrared Photons: 90 9 x 10 Blackbody Power Spectrum Power [Watts/cm 2 /ev] recycled energy h < 0.95eV recycled energy h < 0.8eV Photon Energy [ev] 1 1.2

23 Default Solution: engineer the emissivity spectrum to preferentially produce big photons, h >E g ~50 years of research Recent developments in high-temperature photonic crystals for energy conversion Veronika Rinnerbauer * a, Sidy Ndao bc, Yi Xiang Yeng ab, Walker R. Chan ab, Jay J. Senkevich b, John D. Joannopoulos ab, Marin Soljačić ab and Ivan Celanovic b a Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, MA Energy Environ. Sci., (2012), 5,

24 Thermo-Photovoltaic Converter with Radiant Energy Reflective Means US Patent No. 3,331,707 (Jul. 18, 1967) General Motors Co.

25 For the 1 st time, we have good reflectivity of sub bandgap radiation: Cell Efficiency (%) % 32.2% 31.9% Reflectivity 90% Rear Reflectivity Is Not Enough! Voc (Volts) Reflectivity Jsc (ma/cm 2 ) Reflectivity

26 Thin-Film GaAs Solar Cell: Reflectivity Above and Below BandGap Sub bandgap reflectivity > 92% 100 Sample AD19631 above bandgap anti reflection coating

27 thermophotovoltaic chamber water cooling on all exterior surfaces reflected thermal radiation hot source photovoltaic cells lining inner faces of radiation chamber 280 suns bouncing around internally! Small area photovoltaic cell is adequate.

28 Cross-sectional view of the thermophotovoltaic chamber: T c =20 C water cooling on all sides thermal radiation, recycled back to source photovoltaic films with high rear reflectivity T c =20 C hot source, temperature=t s T c =20 C high reflectivity mirrors at ends T c =20 C

29 Conversion of Heat to Electricity Efficiency (%) Single Junction Cells 1500 C = Radiation Temperature 20 C = Cell Temperature not SQ limit; non ideality ext = % 91% 92% 93% 94% 95% 96% 97% 98% Photovoltaic Cell Infrared Reflectivity in % Convert Heat to Electricity with >50% Efficiency Burn Fuel but 2X efficiency and half the emissions 99%

30 What about furnace efficiency? The only thing of value to us, is the high temperature photons. >90% furnace efficiency is possible. We should use the hot combustion gas to pre-heat the cold air and fuel conducting membrane cold cold recuperator or hot combustion products air, fuel hot heat exchanger h h combustion T=1500C h h

31 Thermo-PhotoVoltaic Hybrid Car: 50kWatt 70cm 70cm 1200 C is equivalent to 100suns to 500suns

32 fuel air exhaust photovoltaic cells lining inner faces of radiation chamber water cooling on all exterior surfaces thermal radiation dollar bill for size scale 20cm thermal radiation chamber heated reaction manifold For home use: 1000 Watt electricity 1056 Watts hot water

33 Side View Radiation chamber thermal losses 10 W t For home use: 1000 Watt electricity 1056 Watts hot water high reflectivity photovoltaic films thermal input into radiation chamber: 4406 W t Advanced Recuperator: recuperated heat 2160Wt combustion products 2340W t fuel 2246W t warm exhaust 130W t electricity 1000W e photovoltaic cell cooling water at 80 C, 1056W t recuperator heat losses 50W t

34 Quad-Copters for civilian & military use: : Duration depends on energy density Lithium battery lasts 20 minutes. Liquid fuel has 50 times higher energy density, would last 16 hours.

35 For Deep Space use, heat Source can be nuclear, SiC pellets at 1500 C.

36 But there is competition from Fuel Cell vehicles; 2H 2 +O 2 2H 2 O requires H 2 storage; (but new H 2 storage technologies are being invented)

37 Conclusions: Opto-electronics can provide electricity. the motive power for hybrid automobiles. (replaces the internal combustion engine) for home electricity and hot water for aviation The automotive power market is 10 bigger than the solar panel electricity market.