Van der Waals-Zeeman Institute, University of Amsterdam “Twee halen - een betalen” Si...

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Van der Waals-Zeeman Institute, University of Amsterdam Twee halen - een betalen Si nano-photovoltaics Tom Gregorkiewicz Slide 2 Preferred solutions for energy Use processes occurring in nature -do not produce new components (nuclear waste, CFC, ) - CO 2, CO, SO 2 do occur in nature but in small quantities (e.g. burning of wood) The scale needs to be small (best negligible) when compared to those occurring naturally Absorption of solar energy is a natural process PV shapes this natural process in the way useful to men, using only a (very) small part Van der Waals-Zeeman Institute, University of Amsterdam Slide 3 Calibrating the energy needs Daily food consumption: 2000 cal/day 100 W ~ 1 kW Solar power: 120.000 TW ~0.02% of the total is enough to power our civilization! 2 kW pp 13 TW (2010) 28 TW (2050) Van der Waals-Zeeman Institute, University of Amsterdam Slide 4 light low/high temperature heat light electricity Main solar energy conversion options Van der Waals-Zeeman Institute, University of Amsterdam Slide 5 light low/high temperature heat light electricity light chemical energy (solar fuels, art. photosynthesis) Main solar energy conversion options Van der Waals-Zeeman Institute, University of Amsterdam Slide 6 Jimmy Carter at SERI (now NREL) May 5, 1978 Oil crisis of the 1970s Dont worry Mr. President, solar will be economical in 5 years! I cant believe he said that. Van der Waals-Zeeman Institute, University of Amsterdam Slide 7 Global warming crisis Barack Obama at Nellis AFB May 2009 Van der Waals-Zeeman Institute, University of Amsterdam Slide 8 Slide 9 Slide 10 Solar electricity solutions Indirect conversion: light-high T heat- electricity Solar thermal energy: photons-to-phonons-to- electrons -without energy storage - with energy storage Van der Waals-Zeeman Institute, University of Amsterdam Slide 11 Solar thermal power Van der Waals-Zeeman Institute, University of Amsterdam Slide 12 Solar thermal power Van der Waals-Zeeman Institute, University of Amsterdam Slide 13 Solar electricity solutions Indirect conversion: light-high T heat- electricity Solar thermal energy: photons-to-phonons-to- electrons -without energy storage - with energy storage Direct conversion: light-to-electricity Photovoltaics: photons-to-electrons -without light concentration - with light concentration Van der Waals-Zeeman Institute, University of Amsterdam Slide 14 load top metal contact bottom metal contact active material (with asymmetry for charges) mobile negative charge mobile positive charge Photovoltaic cell Courtesy W. Sinke, ECN Slide 15 Researchers at Bell Labs, N.J. (USA) 1953, first photovoltaic solar cells based on silicon ( 5%) In 1954, the U.S. News & World Report wrote : ..one day such silicon stripsmay provide more power than all the worlds coal, oil and uranium PV history Van der Waals-Zeeman Institute, University of Amsterdam Slide 16 17 th March 1958: The Vanguard 1 satellite with solar panels - 0.1 watt peak power is put onto orbit PV history Van der Waals-Zeeman Institute, University of Amsterdam Slide 17 Slide 18 Polycrystalline silicon a cheap & easy-to-make alternative Slide 19 Van der Waals-Zeeman Institute, University of Amsterdam Slide 20 PV application limits? Van der Waals-Zeeman Institute, University of Amsterdam Slide 21 Source: Photon International March 2010 Van der Waals-Zeeman Institute, University of Amsterdam Slide 22 Thin film 1979 2009 wafer Si silicon feedstock shortage 2007 2009 22% price decrease for every doubling of cumulative production Source: EPIA, October 2009 Price development Van der Waals-Zeeman Institute, University of Amsterdam Slide 23 Over 90% of todays PV modules are based on Crystalline Silicon Excellent performance modules: ~20% lab: up to ~25% Current status PV Van der Waals-Zeeman Institute, University of Amsterdam Slide 24 Silicon for PV Slide 25 indirect bandgap low emission/absorption rates (at low energies) Van der Waals-Zeeman Institute, University of Amsterdam Silicon and light Slide 26 gap energy heat generation recombination light X X X PV conversion basic concept Van der Waals-Zeeman Institute, University of Amsterdam Slide 27 X X PV conversion loses Van der Waals-Zeeman Institute, University of Amsterdam Slide 28 Shockley-Queisser limit Conversion efficiency maximum for single junction PV cell with E gap =1.1 eV ( 31 %) Van der Waals-Zeeman Institute, University of Amsterdam Slide 29 Optimal bandgap energy Abundant Mechanically strong High mobilities possible Si for photovoltaics Van der Waals-Zeeman Institute, University of Amsterdam Slide 30 Manipulate band-structure Light management: waveguiding, cloaking, multiple reflection, dispersing Si nanowires Si nanocrystals Quantum cutting and pasting Smart solutions for Si PV Van der Waals-Zeeman Institute, University of Amsterdam TGG Slide 31 Si nanocrystals Slide 32 Nanocrystals (NCs) Bandstructure modification induced by quantum confinement Bands quantized energy levels Relaxation of k-vector conservation for indirect bandgap Tuning optical properties Silicon 4.3 nm SiNC Slide 33 Paillard et al., Tolouse Si Nanocrystals in SiO 2 Van der Waals-Zeeman Institute, University of Amsterdam Slide 34 VB CB PL SiNC Van der Waals-Zeeman Institute, University of Amsterdam Si NC photoluminescence Slide 35 VB CB PL SiNC Van der Waals-Zeeman Institute, University of Amsterdam Si NC photoluminescence Slide 36 SiNC Van der Waals-Zeeman Institute, University of Amsterdam Si NC photoluminescence Slide 37 VB CB PL SiNC Auger Van der Waals-Zeeman Institute, University of Amsterdam Si NC photoluminescence Slide 38 Si NC PL saturation Van der Waals-Zeeman Institute, University of Amsterdam Slide 39 photon convertors: size-tunable energy photon limiters only one photon out Van der Waals-Zeeman Institute, University of Amsterdam Si nanocrystals Hot electrons are not used! Slide 40 Using hot electrons: Cutting and emitting photons with Si-NCs Slide 41 PL from SiNCs in SiO 2 Van der Waals-Zeeman Institute, University of Amsterdam Slide 42 exc = 323 nm f = 3.8 MHz MCM PMT 370 det 700 nm resolution ~25 ps ~2 ps PL O-related PL Hot PL Excitonic recombination ~s~s ~ns 1 25 ps 2 100 ps PL from SiNCs d=4.5 nm Slide 43 Hot PL for all the samples Van der Waals-Zeeman Institute, University of Amsterdam Slide 44 3.32 eV 1.17 eV Direct Indirect Si Nanocrystal Theoretical model Van der Waals-Zeeman Institute, University of Amsterdam Slide 45 Pulsed vs. semi-cw excitation 1 10 ps ~s NIR ~ns 420 nm Pulsed ~2 ps ~5 ns 10 100 ps Semi-cw ~s NIR ~ns 420 nm Auger cooling 1 Slide 46 hot PL in Si NC 1000 stronger than in bulk Si hot PL s-PL 5 hot PL s-PL 1 W.D.A.M. de Boer et al. Nature Nanotechnology 2010 Relative efficiency enhanced emission and absorption in the visible Van der Waals-Zeeman Institute, University of Amsterdam Slide 47 Cutting photons with Si NCs Slide 48 Solid state sample: SiO 2 :Si-NCs Colloidal sample: SiNCs in ethanol HF chemical etching: po-Si suspended in ethanol Experimental setup Absolute QE of Si-NCs PL Van der Waals-Zeeman Institute, University of Amsterdam Slide 49 Q.E. for different wavelengths in visible and near UV is constant up to a photon energy threshold of E threshold 2 E gap For larger photon energies a second excitation mechanism takes place Definition relative quantum efficiency: = N em N abs Relative quantum efficiency Van der Waals-Zeeman Institute, University of Amsterdam Slide 50 Multi-exciton generation (MEG) Space-separated quantum cutting (SSQC) E exc 2E gap Quantum cutting with Si-NCs D. Timmerman et al., Nature Photonics (2008) Slide 51 SSQC with SiNCs in SiO 2 E exc >2E gap 1 in 2 out Van der Waals-Zeeman Institute, University of Amsterdam Slide 52 Quantum cutting with Si-NCs QE is constant up to photon energy threshold of h 2E g ~100 % increase of initial value Step-like behavior Two types of Si-NC samples: Si-NCs in SiO 2 po-Si in EtOh In two different calibrated QE setups Van der Waals-Zeeman Institute, University of Amsterdam Slide 53 Shockley-Queisser limit Conversion efficiency up to 44%!!! Slide 54 D. Timmerman et al., under review Nature Materials PV impact Van der Waals-Zeeman Institute, University of Amsterdam Slide 55 XXI st century will begin (Si) Solar Energy Age Reaching ultimate PV cost and performance levels at sufficient sustainability critically depends on (Si) materials development Conclusion you have seen nothing yet Van der Waals-Zeeman Institute, University of Amsterdam Slide 56 TGG at WZI, UvA Van der Waals-Zeeman Institute - UvA Slide 57