Dye-Sensitized Solar Cells Carl C. Wamser Portland State University Nanomaterials Course - June 28, 2006
Energy & Global Warming M.I. Hoffert et al., Nature,, 1998, 395,, p 881 Energy Implications of Future Atmospheric Stabilization of CO 2 Content M.I. Hoffert et al., Science,, 2002, 298,, p 981 Advanced Technology Paths to Global Climate Stability: Energy for a Greenhouse Planet
The Kaya Identity N = population GDP/N E/GDP C/E = gross domestic product per person = energy intensity (per GDP unit) = carbon intensity (per energy unit) Annual Energy = N*(GDP/N)*(E/GDP) Annual CO 2 = N*(GDP/N)*(E/GDP)*(C/E)
Global Totals/Future Trends Annual Energy = N*(GDP/N)*(E/GDP) 10 TW 30-40 TW by 2050 ( 1990 data cited in Hoffert s Nature paper ) 5.3 billion ~9 billion by 2050 $4100 rising 1.6%/yr 4.3 kwh/$ falling 1.0%/yr Annual CO 2 6 Gtons 350 ppm rising to?? = N*(GDP/N)*(E/GDP)*(C/E) 64 gc/kwh falling by??
Conclusions Stabilization of atmospheric carbon will require immense amounts of carbon-free energy in the near future (2050): 550 ppm - about 15 TW 450 ppm - about 25 TW 350 ppm - over 30 TW M.I. Hoffert et al., Nature, 1998, 395,, p 881
The ENERGY REVOLUTION (The Terawatt Challenge) Sources of Energy Supply - Worldwide 50 45 40 35 30 25 20 15 10 5 0 Oil Coal Gas Source: Internatinal Energy Agency Fission Partners in Science January 18, 2003 2002 40 13 Terawatts 35 30-50 Terawatts Biomass Hydroelectric 0.5% Solar, wind, geothermal R. E. Smalley Rice University 50 45 30 25 20 15 10 5 0 Oil Coal Gas 2050 Fission Biomass Hydroelectric Solar, wind, geothermal
Conclusions Researching, developing and commercializing carbon-free primary power technologies capable of 10-30 TW by the mid- 21st century could require efforts, perhaps international, pursued with the urgency of the Manhattan Project or the Apollo space programme. M.I. Hoffert et al., Nature, 1998, 395,, p 881
Photovoltaic Land Area Requirements 3 TW = approx total energy currently used in U.S. 3 TW 20 TW 20 TW = minimum carbon-free total energy needed by 2050 Graphic from Nate Lewis Caltech
Photovoltaic Land Area Requirements 6 Boxes at 3.3 TW Each
Photosynthesis ( 1961 Nobel Prize )
Photosynthetic Reaction Center ( 1988 Nobel Prize ) http://www.mpibp-frankfurt.mpg.de/~michael.hutter/rcenter.html
Artificial Photosynthesis Any solar energy conversion method that uses some aspects of nature s strategy, compounds, or both Strategy Photoinduced electron transfer across a membrane Compounds Chlorophyll dyes and electron- transfer mediators
Thermodynamic Criteria Optimize energy conversion (photopotential) e - Match the dye bandgap to the solar spectrum optimum λ bg ~ 1000 nm, efficiency ~ 30% hν h + Match the redox potentials (valence/conduction bands) ETM dye HTM
Kinetic Criteria Optimize quantum yield (photocurrent) Fast forward reactions: a) Light absorption b) Charge separation c) Hole and electron mobilities Slow back reactions: d) Excited state deactivation e) Charge neutralization ETM dye HTM
Dye-Sensitized Solar Cell Dyes Ru(bipy) 3 derivatives (N3) Porphyrins Electron-transport media n-type semiconductors Nanoparticulate TiO 2 Hole-transport media p-type semiconductors Redox electrolytes ( I - / I 3 - ) Conductive polymers
The Grätzel Cell B. O Regan & M. Grätzel, Nature (1991) 353, 737-740.
The Grätzel Cell Optimized output Short-circuit current I sc ~ 20 ma/cm 2 ( V vs SCE ) -0.6-0.9 Open-circuit voltage V oc ~ 0.7 V Quantum yield ~ 1 ~ +0.8 +0.2 Efficiency ~ 11% TiO N3 2 I - /I - 3
hν Preparation of a Grätzel Cell I - /I 3 - I SC ~ 20 ma/cm2 ITO or FTO ITO or FTO V OC ~ Φ ~ 1 0.7 Volts Efficiency ~ 11% TiO 2 Porphyrin
Operation of a Grätzel Cell ITO TiO 2 TCPP I - 3 / I- ITO -0.6-0.9 Porphyrin LUMO hv +0.2 +2.6 +1.1 P + Porphyrin HOMO V oc = 0.7 V ; I sc = 20 ma/cm 2
Photopolymerization - Proposed Mechanism e - hv e - Stage I x10 10n H + HOOC NH 2 NH 2 NH 2 5n H 2 TiO 2 NH N N HN e - Stage II H N H N e - HOOC COOH N H N H n 5,10,15-tris(4-carboxyphenyl)-20-(4-aminophenyl)porphyrin (TC 3 APP)
DSSC Expt: Procedures 1. Prepare Working Electrode TiO 2 underlayer / nanoparticles / overlayer Dye adsorption ( TCPP in EtOH ) 2. Prepare Counter Electrode Graphite on FTO (F-doped tin oxide) 3. Assemble Cell Redox electrolyte solution ( I - - / I 3 ) 4. Irradiate Cell Monitor light intensity / photocurrent / photovoltage
DSSC Expt: Procedures 1. Prepare Working Electrode TiO 2 underlayer - dip in Ti(iOPr) 4 Nanoparticle layer - dip in TiO 2 slurry Overlayer (skipped this time) Bake at 450 for 30 minutes ( A pre-prepared electrode will be provided for testing while your electrode is baking )
DSSC Expt: Procedures 2. Prepare Counter Electrode Graphite on FTO (F-doped tin oxide) (catalyst for iodide/triiodide reaction )
DSSC Expt: Procedures 3. Dye Adsorption Pre-prepared electrode will have TCPP, adsorbed from EtOH (takes overnight) You will soak your electrode in blackberry juice (natural anthocyanine dyes) takes about 15 minutes
DSSC Expt: Procedures 4. Assemble Cell Working electrode (with dye) a) TCPP pre-prepared electrode b) Blackberry electrode, rinsed and dried Add redox electrolyte solution ( I - / I 3- ) Assemble sandwich cell
Slide and back electrode in test fixture
DSSC Expt: Procedures 5. Irradiate Cell Install cell in test fixture Install test fixture in Vertical Optical Bench (VOB) Scan applied voltage from -700 to +100 mv Monitor light intensity Monitor photocurrent vs. applied voltage (iv curve) Capture data on PC, export to Excel Save to your personal USB drive
Slide being tested in the VOB
Light from the VOB Through 16mm hole
Light shining through test slide
Cell being tested on VOB
iv Curve for TCPP Cell Re-Test of KJ0216 NB-90-21 KJ216_22 DipCoat FKJ0172 Pt (NB-80-85) microamps 1500 1300 1100 900 700 500 300 100-800 -700-600 -500-400 -300-200 -100-100 0 100 mvolts
Power Curve for TCPP Cell Re-Test of KJ0216 NB-90-21 KJ216_22 DipCoat FKJ0172 Pt (NB-80-85) 0.6000 0.5000 mwatts 0.4000 0.3000 0.2000 0.1000 0.0000-800 -700-600 -500-400 -300-200 -100 0 100 mvolts
iv Curve for TCPP Cell microamps Re-Test of KJ0216 NB-90-21 KJ216_22 DipCoat FKJ0172 Pt (NB-80-85) 1500 1300 1100 900 700 500 300 100-100 -800-700 -600-500 -400-300 -200-100 0 100 Voc Pmax mvolts Fill Factor Isc
Test and Performance Parameters Light source: Tungsten halide lamp Intensity = 97 mw/cm 2 = 0.97 Sun Irradiated area = 0.71 cm 2 P in = 69 mw V oc = 652 mv I sc = 1.3 ma P max = 0.47 mw Fill Factor = P max / ( V oc * I sc ) = 0.55 Efficiency = P max / P in = 0.68 %
DSSC Expt: Report Check the class website for updated info Title / Abstract Introduction / Background Experimental Procedure / Apparatus Results / Discussion Conclusions Compare all performance data for both types of cells you tested
DSSC Expt: References Demonstrating Electron Transfer and Nanotechnology: A Natural Dye-Sensitized Nanocrystalline Energy Converter, G. P. Smestad and M. Grätzel, J. Chem. Educ., 1998, 75(6), 752-756. Adsorption and Photoactivity of Tetra(4-carboxyphenyl) porphyrin on Nanoparticulate TiO2, S. Cherian and C. C. Wamser, J. Phys. Chem. B, 2000, 104, 3624-3629. Basic Research Needs for Solar Energy Conversion, U.S. Department of Energy, 2005. Note - all of the above references can be found as.pdf files on Professor Wamser s website: http://chem.pdx.edu/~wamserc/research/