Universität Karlsruhe (TH)

1

Preliminary schedule

1. Introduction, The Sun2. Semiconductor fundamentals3. Solar cell working principles / pn-junction solar cell4. Silicon solar cells5. Copper-Indiumdiselenide solar cells6. Cell optimization and highly efficient device concepts7. Modules and system integration8. Organic photovoltaics9. Dye sensitized solar cells

10. Economics and profitability11. Other renewable energies12. Excursion

Course schedule

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2Dye sensitized solar cells

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3Background

Dr. Michael Grätzel

1991: Dr. Michael Grätzel created the„Grätzel Cell“ (dye sensitized

solar cell – DSSC) at EPFL

Promising technology:low costeasy manufacturingpower conversion efficiency of

10%

Companies:Dyesol (Queanbeyan, Australia)G24i (Wentloog, Cardiff)

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4Companies

G24i: licensed EPFL technology

Dyesol: selling materials (dyes, electrolytes,…) and equipment (screen printer, dye

applicator, electrolytefilling machine,…)

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5Schematic structure

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6Schematic structure

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7TiO2 photoelectrode

TiO2 film SEM photograph

TiO2 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 forsufficient electrolyte film penetration

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8Ru complex photosensitizer

Typical Ru complexsensitziers developed byGrätzel‘s group

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9Ru complex photosensitizer

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10Ru complex photosensitizer

N3 dye adsorbed on the (101) surface of TiO2

Ru complexes with carboxylgroups to anchor the TiO2surface

Coverage of the TiO2surface with N3 dye near100%

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11Redox electrolyte

Electrolyte contains I-/I3- redox ions for electron mediation

between the TiO2 photoelectrode and the counter electrode

Cell performance depends on:- counter cations of iodides (e.g. Li+, Na+, K+)- viscosity of solvents

DyeRedox

ElectrolyteTiO2

I- I3-

Cathode

e-

e-

e-

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12Counter electrode

DyeRedox

ElectrolyteTiO2

I- I3-

Cathode

e-

e-

e-

I3- ions are re-reduced to I- ions at the counter electrode

Pt coated on TCO (approx. 200 nm) or carbon are typically used

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13Sealing materials

Prevent leakage of the electrolyte and the evaporation of thesolvent

Chemical and photochemical stability against the electrolytecomponent, iodine and the solvent is required

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14Primary processes

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15Photovoltaic performance

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16Photovoltaic performance

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17Charge-transfer kinetics

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18Dark current

Recombination of injected electrons with I3- ions: −−− →+ ITiOeI 3)(2 23

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19Electron transport in TiO2 film

Very small electron conductivity in TiO2 film

Conductivity in DSSC significantly increased due to electroninjection from the photosensitizers under photon irradiation

Conductivity and photocurrent response increase with increasinglight intensity

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20Characteristics

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

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21DSSC Fabrication

Preparation of TiO2 colloid

Preparation of the TiO2 electrode

Dye fixation onto the TiO2 film

Redox electrolyte

Counter electrode

Assembling the cell

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22DSSC Fabrication

Preparation of TiO2 colloid

Preparation of the TiO2 electrodea) Doctor bladingb) Screen printing

Dye fixation onto the TiO2 film

Redox electrolyte

Counter electrode

Assembling the cell

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23DSSC Fabrication

Preparation of TiO2 colloid

Preparation of the TiO2 electrodea) Doctor bladingb) Screen printing

Dye fixation onto the TiO2 film

Redox electrolyte

Counter electrode

Assembling the cell

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24DSSC Fabrication

Preparation of TiO2 colloid

Preparation of the TiO2 electrodea) Doctor bladingb) Screen printing

Dye fixation onto the TiO2 film

Redox electrolyte

Counter electrode

Assembling the cell

Universität Karlsruhe (TH)

25DSSC Fabrication

Preparation of TiO2 colloid

Preparation of the TiO2 electrodea) Doctor bladingb) Screen printing

Dye fixation onto the TiO2 film

Redox electrolyte

Counter electrode

Assembling the cell

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26DSSC Fabrication

Preparation of TiO2 colloid

Preparation of the TiO2 electrodea) Doctor bladingb) Screen printing

Dye fixation onto the TiO2 film

Redox electrolyte

Counter electrode

Assembling the cell

Sputtering process

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27DSSC Fabrication

Preparation of TiO2 colloid

Preparation of the TiO2 electrodea) Doctor bladingb) Screen printing

Dye fixation onto the TiO2 film

Redox electrolyte

Counter electrode

Assembling the cell

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28Cell Performance

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29New oxide semiconductor film photoelectrodes

Replace TiO2 by: ZnO η = 2.5%SnO2 η = 0.65%Nb2O5 η = 2.6%In2O3 η = 0.38%SrTiO3η = 1.8%

Combine two oxide semiconducter materialsTennakone et al. SnO2/ZnO η = 8%

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30New dye photosensitizers

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31Organic and natural dye photosensitizers

variety of structures for molecular design

cheaper than metal complexes

large absorption coefficients

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32New electrolyte

Replace volatile organic solvents by

room-temperature ionic liquids (molten salts)

high ion conductivity

electrochemical stabitiy

nonvolatility

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33Solid state DSSCs

1, conducting F-doped SnO2-coated glass2, compact TiO2 layer3, dye-sensitized heterojunction4, gold electrode

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34Quasi solid state DSSCs

Gelator used to replace liquid electrolyte

Gelator added to the electrolyteat elevated temperature

Hot electrolyte solution appicatedon dye-coated TiO2 layer

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35Prospects

Improvement of efficiency

Long-term stability for outdoor applications

Solid electrolyte

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36Prospects