Silicon Photonics University of Pune Physics Short Course

Transcription

1 Silicon Photonics University of Pune Physics Short Course August 11-13, 16, 17, 2010 India-U.S. Professorship Award Lectures S.Saini (Queens College), J. Michel (MIT) 2010 Sub-Micron Planar Platform - E-P Convergence - Materials Integration Device Physics - Materials Science Sajan Saini Queens College City University of New York Sponsored by: The Indo-U.S. Science & Technology Forum and The American Physical Society

2 Lecture 1: Introduction to Si Photonics Lecture 2: Waveguides & Mode-Engineered Devices Lecture 3: Resonators & Photodetectors Lecture 4: Modulators & Lasers Lecture 5: Photonics in 3 rd Gen. Photovoltaics Electronic-Photonic Integration Confinement Physics Scatering mechanisms, Si-compatible waveguides Turns, splitters, rotators, couplers WDM & standing/traveling wave cavities Si vs. Ge detectors Plasma dispersion & electroabsorption modulators III integrated lasers, ultra-high Q, Ge laser The case for a solar economy 3rd Gen. PV materials & devices 62

3 Applications: Photonics for 3 rd Gen Photovoltaics Availability of solar power Solar versus combustible energy sources 1st, 2nd, 3rd Generation PV examples Photonics in PV

4 Modernity: an Energy Intensive Way of Life Visible spectral emission from terrestrial surface Modern economy is energy intensive: need cheaper, cleaner sources of power India 64

5 Solar Powered Energy Economy Visible spectral emission from terrestrial surface Solar power density on terrestrial surface Majority of terrestrial surface plentiful with solar reserves Power availability (A=1 m 2, ~0.3) Africa, South America, Australia: ~187 W (daytime) India, Arizona: ~175 W (daytime) 65

6 Why Renewable Energy? Solar spectrum (on Earth) Citizen: electric transportation (long-term) = transport cost Governments: shift in national security policy The Planet: reduce green house gas production (CO 2, H 2 O, CH 4 ) T Climate Change consequences: Polar ice melting: ocean salinity, alter ocean currents Warmer atmosphere & oceans: severe hurricanes & blizzards Warmer ocean: water expands, sea level (20 cm / 100 yrs) IF polar ice caps melted, sea level 70 m Solar reserves are abundant resource: 1 hour of sunlight on earth = all the energy used globally by people in one year!!! Question: how many Si solar panels (PV area) required? Solar Energy is long lasting - ~5 billion years 66

7 Renewable Energy Sources Solar 1.2 x 10 5 TW at Earth surface TW practical land sites Wind 2-4 TW extractable Tide/Ocean Currents 2 TW gross Geothermal 12 TW gross over land small fraction recoverable energy gap ~ 14 TW by 2050 ~ 33 TW by 2100 ( Y. Yi, College of Staten Island, CUNY, 2010) Biomass 5-7 TW gross all cultivatable land not used for food Hydroelectric 4.6 TW gross 1.6 TW technically feasible 0.9 TW economically feasible 0.6 TW installed capacity 67

8 Coal: the Dirty Opponent Source: U.S. Energy Information Administration (Oct 2008). U.S. Annual Electrical Energy flow (2008) in Quads (1 Quad = BTU ~10 18 J) Coal-fired thermal plants consume a disproportionate amount of input power for production Conversion losses are dominated by thermal plants (coal, natural gas) 68

9 PV Solar Cell Structure & Materials Efficiency vs energy for common PV materials 1st Gen: Si homojunction Peak absorption in visible spectrum (92% of PV market) 2nd Gen: increase vis absorption Amorphous thin film Si CuInGaSe 2 (CIGS), CdTe Organic PV, Dye-sensitized PV 3rd Gen: device & materials eng. for >30% Tandem solar cell (broadband absorption) Intermediate band gap solar cell (sub band gap absorption) 69

10 1 st Generation Solar Cells Bulk Silicon Single crystal, polycrystalline ~92% of PV market Si homojunction ~30% single-junction efficiency (Schockley-Quiesser limit) High vis-absorption Inefficient UV absorption IR photon unabsorbed (below band gap) Challenges Indirect bandgap Decrease impurities, grain boundaries and dislocations recombination Produce larger ingots, ribbons and boules Increase growth speeds Major players Sun Power, Shell Solar, BP Solar (U.S.) Suntech Power, Yingli, JA Solar, Trina Solar (China) Sharp Corp. (Japan) Q-Cells (Germany) a rigorous analysis of the worldwide supply position shows there is insufficient silicon feedstock to meet the planned cell manufacturing capacity expansion, overall PV market growth will be restricted as a result. solarbuzz.com ( Y. Yi, College of Staten Island, CUNY, 2010) 70

11 2 nd Generation Solar Cells Thin Films a-si, CdTe, CI(G)S 7% of PV market p-n or p-i-n heterojunction(s) Deposited by evaporation, sublimation, spraying, sputtering, electrodeposition, or chemical vapor deposition Challenges Improve module Efficiencies!!! a-si: United Solar Ovonic, BP Solar, EPV (Stabilized eff. 6-8%) a-si: Moser Baer (Noida, India) SunFab line, 2009 Poly-Si: Kyocera (Japan) CdTe: First Solar, Antec Solar (7-11% module eff.) CI(G)S: Shell Solar, Global Solar (7-13% module eff.) 71 ( Y. Yi, College of Staten Island, CUNY, 2010)

12 3rd Generation PV Multijunction Tandem Solar Cells Solar Photon Flux (ma/cm 2.eV) 70 Eg Eg2 Eg1 Sunlight E g1 E g2 E g Energy (ev) Tandem PV Cells use multiple p-n junctions to absorb different ranges of the solar spectrum and hence reduce photogenerated electron energy loss via thermalization (phonon emission). 72 ( Y. Yi, College of Staten Island, CUNY, 2010)

13 3rd Generation PV Organic Solar Cells Bulk Heterojunction Intimate mixture of D/A, usually polymer (donor) and C 60 derivative (acceptor) Exciton diffusion length ~ 10 nm Want all excitons created within a diffusion length of interface < 5% efficiency Challenges Lifetimes = thousands of hours Device degradation Phase separation lowers efficiency polymer has low mobility so films are too thin for full absorption e - Major players: academia, Konarka (U.S.) 100 nm Glass Transparent electrode _ + Metal electrode MRS Bulletin, Vol 30, Jan ( Y. Yi, College of Staten Island, CUNY, 2010)

14 3rd Generation PV Dye-Sensitized Solar Cells Grätzel Cell Dye injects e - into nanocrystalline TiO 2, dye is regenerated by solid or liquid electrolyte Light absorption and charge transport are separated Up to 12% efficiency High surface area = more dye = higher current Challenges liquid electrolyte is optically dense and cells leak over time highest efficiencies obtained with liquid electrolyte and Ti foil electrode Solid-state cells not as efficient (4%) Dye-sensitized Major players: Konarka Claim 6-10% efficiency Roll-to-roll hybrid Grätzel/organic cell Trying to partner with other companies J. Am. Ceram. Soc., 80 [12] (1997) 74 ( Y. Yi, College of Staten Island, CUNY, 2010)

15 3rd Generation PV Concentrating Solar Cells Concept: turn Si PV into a micro device benefit from Moore s Law (Economy of Scale) Major players: Sharp Corp. (Japan), SolFocus (U.S.), Spectrolab (U.S.) Individual Lens: 7.4 x 7.4 Parquet Size: x Material: Acrylic Focal Length: Focal Point Size:.5 x.5 Optical Efficiency: 84% 75 ( Y. Yi, College of Staten Island, CUNY, 2010)

16 Evolution in PV Efficiency 76 ( Y. Yi, College of Staten Island, CUNY, 2010)

17 Evolution in PV Efficiency Sanyo HIT (Heterojunction with Intrinsic Thin Layer: c-si + a-si ( Source: B. Nelson and S. Robbins, Introduction to Photovoltaic Technologies, Short Course, 34th IEEE PVSC (2009). 77

18 Photonics in 3rd Generation PV Nanoparticles: scintillators, intermediate band gap absorbers E. Mutlugun, H. Demir et al., Photovoltaic nanocrystal scintillators hybridized on Si solar cells for enhanced conversion efficiency in UV, Opt. Express v.16(6), p (2008). V. Svrcek et al., Silicon nanocrystals as light converter for solar cells, Thin Solid Films v , pp (2004). CdSe, Si scintillators: absorb UV and downconvert to visible light, for Si PV Ge QD doped within Si: sub-band gap absorption, Type II offset minimizes carrier recombination S V Kondratenko, et al., The lateral photoconductivity of Si/Ge structures with quantum dots, Semicond. Sci. Technol. v.21. pp (2006). 78

19 Photonics in 3rd Generation PV Nanoparticles: tandem, hot carrier cells Templated lattice constant: artificial band gap materials Match Fermi levels to metal contacts: reduces carrier thermalization G. Conibeer, M. Green et al., Silicon nanostructures for third generation photovoltaic solar cells, Thin Solid Films, v , pp (2006). 79

20 Photonics in 3rd Generation PV Photonic Crystals: scattering incident light into solar cell plane J. Song, X.W. Sun et al., Tunable Fano resonance in photonic crystal Slabs, Opt. Express, v.14(19), p.8812 (2006). Fano resonances scatter incident wavelengths into high dielectric states 80

21 Renewable Energy: Long-term Concerns Geology and location Solar tracking Efficient battery storage and low resistance transport Smart grid for green energy? Solar thermal Hydrogen generation 81 ( Y. Yi, College of Staten Island, CUNY, 2010)