Overview of Photovoltaic Energy Conversion

Transcription

1 Overview of Photovoltaic Energy Conversion

2 Topics Solar Energy Economics Photovoltaic Technologies Challenges and Opportunities II-VI Solar Cells

3 November 20, 2006

4 U.S. Energy Overview (Quadrillion BTU)

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6 CO 2 Emissions US ~ 20 metric tons / capita / year An average person generates 0.33 metric tons per year through respiration Metric tons per capita per year China ~ 2.2 metric tons / capita / year Source: NY Times

7 2005 U.S. Energy Consumption

8 U.S. Energy Consumption Overview Year (%) Total (Quadrillion BTU) % Fossil Fuels % Coal % Coal Coke Net Imports % Natural Gas % Petroleum % Electricity Net Imports % Nuclear Electric Power % Renewable Energy % Biomass % Biofuels % Waste % Wood Derived Fuels % Geothermal Energy % Hydroelectric Conventional % Solar/ PV Energy % Wind Energy %

9 U.S. Electric Power Net Generation, 2006 Total = 4,065 Billion KWh (10% from Renewables and Hydroelectric) 45.6% 42.4% 38.3% 72.6% 89.6% Capacity factor is highest for nuclear power plant

10 U.S. Electricity Net Generation in thousand kwh: Total (All Sectors), Note: Solar/PV includes solar thermal

11 Solar Energy Production Factor Contour Map in KWh / KW-year ~ yearly hours of sunshine Rochester 4.1 hr/day 6.59 hr/day Tucson

12 Global PV Production and Production Capacity Trend

13 2005 PV Production (MW) by country

14 PV Production (Cells)

15 2006 PV Production and Production Capacity in U.S.

16 PV Module and System Price

17 Source: solarbuzz.com

18 PV Industries in U.S. 2007*(+50%) 309 Peak MW Total including 2007 = 927 Peak MW

19 U.S. PV Cell and Module Revenues 2006 Thin-film PV market share ~ 30%

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21 Renewable Porfolio Standard Charge Delivery Charge Supply Charge Total electric utility charge = $62.55 Tang s household data (averaged over 38 months): Usage: 7284 kwh per year (607kWh / month) Charge: $795 per year ($66 / month) Average cost of electricity = $0.109 per kwh

22 Incentives (2006) Federal Tax Credit: $2000 NYS incentives (NYSERDA) 100% Tax exemption $4.00 per watt for grid-connected homes, $4.50 per watt for energy-star homes Up to 60% of total cost 4 kw PV $6/W & 30 year life: = 41.8 cents / kwh (before incentives) = 13.2 cents / kwh (after incentives) Vs 10.9 cents / kwh from RGE

23 Solar Cell Technologies Si-based solar cells Crystalline Si Poly-Si Thin Si Thin-film solar cells Cu(In,Ga)Se 2 CdS/CdTe Emerging solar cells TiO 2 -dye sensitized cells Organic cells PV concentrators

24 Solar spectrum and max. conversion for single-junction solar cells Si GaAs a-si AM1.5 = 1 kw/m 2

25 Solar Cell 101 Equivalent circuit I d I = I o [exp(qv/nkt)-1] - I ph V oc = n(kt/q) ln[(i sc /I o )+1] I sc = I ph P max = V oc x I sc x FF

26 Single-junction limit DOE_BES report -

27 Sunpower c-si solar module Module efficiency ~ 18%!

28 Triple-junction a-si solar cells on stainless steel 1000 w/m 2 Area = 1.12 m 2 Module efficiency = 6%

29 Thin-Film PV CdS/CdTe fastest growth First Solar CdS/CdTe thin-film PV Module efficiency ~ 9% Production capacity: 75MW in Ohio 100MW in Germany (under construction) 100MW in Malaysia (announced)

30 DSC Modules from STI (an Australian company, setup in 2001) Flexible DSC from Konarka Module efficiency < 5%

31 Compact TiO2 Porous TiO2 TiO2-DSC Cells Graetzel Cells Hole-transport Acc. Chem. Res. 2000, 33,

32 Best DSC performance

33 Single-junction limit 5.5% DOE_BES report -

34 Organic Bi-layer Photovoltaic Cell C.W. Tang, Appl. Phys. Lett. 48, 183 (1986) Ag 600 A 200 A FF=0.65 ITO AM2 EFF= 1% 10-3 A/cm^ Volt

35 Organic heterojunction photovoltaic structure light Efficiency is limited by short exciton diffusion length ~ nm

36 D: CuPc Organic Heterojunction 5.2eV 3.5eV 6.1eV 4.6eV Vacuum Level 1.7eV E A LUMO A: PTCBI IP 0.9eV 1.7eV HOMO DONOR ACCEPTOR

37 Organic Heterojunction DONOR ACCEPTOR

38 (1) η A > 50% Organic Heterojunction Optical excitation (~10-15 s) η A Optical absorption length ~ 1000Å

39 Organic Heterojunction Exciton relaxation ( s) (1) η A > 50% η RELAX Lattice polarization: E B = 0.1-1eV Necessity for heterojunction

40 Organic Heterojunction Exciton diffusion (10-9 s) (1) η A > 50% η ED (2) η ED ~ 10% Exciton diffusion length ~ Å

41 Organic Heterojunction Exciton dissociation by charge-transfer (~10-13 s) (1) η A > 50% (2) η ED ~ 10% η CT (3) η CT ~ 100% Ultrafast process (~100fs) Very efficient cf. MDMO-PPV/PCBM: 50fs, Zerza, et al., Synth. Metals 119, 637 (2001)

42 Charge collection: overcome Coulomb attraction barrier (10-6 s) (1) η A > 50% Organic Heterojunction (2) η ED ~ 10% η CC (3) η CT ~ 100% (4) η CC ~ 100% r th r th P. Peumans and S.R. Forrest, submitted.

43 (1) η A > 50% Organic Heterojunction Exciton diffusion is limiting step (2) η ED ~ 10% η CC (3) η CT ~ 100% (4) η CC ~ 100% η EQE = η A. η ED. η CT. η CC ~ 10%

44 CuPc PTCBI PTCBI PL 2 Exciton Diffusion Length PL 1 PL 1 /PL 2 Photoluminescence quenching Assume continuum, isotropic diffusion L D =(30±3)Å 0.2 experiment theory Thickness [Å] Peumans et al., J. Appl. Phys. 93, 3693 (2003).

45 Bulk Heterojunction OPV 0.93% 2.5% Brabec, Solar Energy Materials & Solar Cells 83 (2004)

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47 Tandem Organic Photovoltaic Cell Tang, unpublished work 0.0 Volt cells cells ma/cm^2 1 Cell 2.0 * Cells connected electrically in series and optically parallel

48 Solar Spectrum ev 1.55 ev 1.18 ev 3-stack tandem OSC Cathode Solar Power Flux W /m^2/nm Long λ Unit Medium λ Unit Short λ Unit Interconnects 0.2 S M L Anode Wavelength (nm) Spectral Range, nm S ( ) M ( ) L ( ) ma/cm Min Photon energy, ev Voc, v Eff. w/w; FF = % 5.53% 4.21% Eff. Total 17.03% n i p Single-unit p-i-n OSC

49 20th European Photovoltaic Solar Energy Conference, 6 10 June 2005, Barcelona, Spain PATHS TO ULTRA-HIGH EFFICIENCY (>50% EFFICIENT) PHOTOVOLTAIC DEVICES C. B. Honsberg and A.M. Barnett DARPA sponsored VHESC project ($52M)

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51 Grand Challenge: 1TW photovoltaic power generation by 2050? Will need: Much lower cost Higher efficiency Shorter energy payback Longer life Recyclable / disposable New technologies?

52 Solar Paint?