Course schedule 1 Preliminary schedule 1. Introduction, The Sun 2. Semiconductor fundamentals 3. Solar cell working principles / pn-junction solar cell 4. Silicon solar cells 5. Copper-Indiumdiselenide solar cells 6. Cell optimization and highly efficient device concepts 7. Modules and system integration 8. Organic photovoltaics 9. Dye sensitized solar cells 10. Economics and profitability 11. Other renewable energies 12. Excursion
Dye sensitized solar cells 2
Background 3 1991: Dr. Michael Grätzel created the Grätzel Cell (dye sensitized solar cell DSSC) at EPFL Promising technology: low cost easy manufacturing power conversion efficiency of 10% Companies: Dyesol (Queanbeyan, Australia) G24i (Wentloog, Cardiff) Dr. Michael Grätzel
Companies 4 Dyesol: selling materials (dyes, electrolytes, ) and equipment (screen printer, dye applicator, electrolyte filling machine, ) G24i: licensed EPFL technology
Schematic structure 5
Schematic structure 6
TiO 2 photoelectrode 7 TiO 2 collodial solution (or paste) sintered at 450 500 C Film thickness typ. 10 µm Roughness factor > 1000 gives large actual surface Porosity of 50-70% needed for sufficient electrolyte film penetration TiO 2 film SEM photograph
Ru complex photosensitizer 8 Typical Ru complex sensitziers developed by Grätzel s group
Ru complex photosensitizer 9
Ru complex photosensitizer 10 Ru complexes with carboxyl groups to anchor the TiO 2 surface Coverage of the TiO 2 surface with N3 dye near 100% N3 dye adsorbed on the (101) surface of TiO 2
Redox electrolyte 11 e - I - I 3 - e - TiO 2 e - Dye Redox Electrolyte Cathode Electrolyte contains I - /I 3 - redox ions for electron mediation between the TiO 2 photoelectrode and the counter electrode Cell performance depends on: - counter cations of iodides (e.g. Li +, Na +, K + ) - viscosity of solvents
Counter electrode 12 e - I - I 3 - e - TiO 2 e - Dye Redox Electrolyte Cathode I 3 - ions are re-reduced to I - ions at the counter electrode Pt coated on TCO (approx. 200 nm) or carbon are typically used
Sealing materials 13 Prevent leakage of the electrolyte and the evaporation of the solvent Chemical and photochemical stability against the electrolyte component, iodine and the solvent is required
Primary processes 14
Photovoltaic performance 15
Photovoltaic performance 16
Charge-transfer kinetics 17
Dark current Recombination of injected electrons with I 3 - ions: 18 I3 + 2e ( TiO2) 3I
Electron transport in TiO 2 film 19 Very small electron conductivity in TiO 2 film Conductivity in DSSC significantly increased due to electron injection from the photosensitizers under photon irradiation Conductivity and photocurrent response increase with increasing light intensity
Characteristics 20 High energy conversion efficiency Low-cost fabrication Abundant supply of component materials Good potential for colorful, adaptable consumer products Low potential for environmental pollution Good recycability
DSSC Fabrication 21 Preparation of TiO 2 colloid Preparation of the TiO 2 electrode Dye fixation onto the TiO 2 film Redox electrolyte Counter electrode Assembling the cell
DSSC Fabrication 22 Preparation of TiO 2 colloid Preparation of the TiO 2 electrode a) Doctor blading b) Screen printing Dye fixation onto the TiO 2 film Redox electrolyte Counter electrode Assembling the cell
DSSC Fabrication 23 Preparation of TiO 2 colloid Preparation of the TiO 2 electrode a) Doctor blading b) Screen printing Dye fixation onto the TiO 2 film Redox electrolyte Counter electrode Assembling the cell
DSSC Fabrication 24 Preparation of TiO 2 colloid Preparation of the TiO 2 electrode a) Doctor blading b) Screen printing Dye fixation onto the TiO 2 film Redox electrolyte Counter electrode Assembling the cell
DSSC Fabrication 25 Preparation of TiO 2 colloid Preparation of the TiO 2 electrode a) Doctor blading b) Screen printing Dye fixation onto the TiO 2 film Redox electrolyte Counter electrode Assembling the cell
DSSC Fabrication 26 Preparation of TiO 2 colloid Preparation of the TiO 2 electrode a) Doctor blading b) Screen printing Dye fixation onto the TiO 2 film Redox electrolyte Counter electrode Assembling the cell Sputtering process
DSSC Fabrication 27 Preparation of TiO 2 colloid Preparation of the TiO 2 electrode a) Doctor blading b) Screen printing Dye fixation onto the TiO 2 film Redox electrolyte Counter electrode Assembling the cell
Cell Performance 28
New oxide semiconductor film photoelectrodes 29 Replace TiO 2 by: ZnO η = 2.5% SnO 2 η = 0.65% Nb 2 O 5 η =2.6% In 2 O 3 η = 0.38% SrTiO 3 η =1.8% Combine two oxide semiconducter materials Tennakone et al. SnO 2 /ZnO η =8%
New dye photosensitizers 30
Organic and natural dye photosensitizers 31 variety of structures for molecular design cheaper than metal complexes large absorption coefficients
New electrolyte 32 Replace volatile organic solvents by room-temperature ionic liquids (molten salts) high ion conductivity electrochemical stabitiy nonvolatility
Solid state DSSCs 33 1, conducting F-doped SnO 2 -coated glass 2, compact TiO 2 layer 3, dye-sensitized heterojunction 4, gold electrode
Quasi solid state DSSCs 34 Gelator used to replace liquid electrolyte Gelator added to the electrolyte at elevated temperature Hot electrolyte solution appicated on dye-coated TiO 2 layer
Prospects 35 Improvement of efficiency Long-term stability for outdoor applications Solid electrolyte
Prospects 36