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A review on Dye-Sensitized Solar Cells

NanoMaster-SemiConductors
by

Ernesto Baena

on 17 September 2013

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Transcript of A review on Dye-Sensitized Solar Cells

A Landscape of
Dye Sensitized Solar Cells

Ernesto Baena Murillo
Asignatura: “Semiconductores: Fundamentos y dispositivos”
Máster en Nanociencia y Nanotecnología Molecular
Universidad de Alicante - 2011

"Solar Cell"
"Solar Cell" + Dye
Efficiencies
Molecular Sensitizers
Working Principle
Air Mass
Archetypes
Hydrophobic Sensitizers
1. Reduce desorption
2. Recombination inhibition
Strategies
Different Metal Oxides as Semiconductor
Surface Passivation
Long Aliphatic Chains in the Sensitizer
High Molar Extinction
Coefficient Sensitizers
Lowest Metal-to-Ligand Charge transfer:
-400 nm: 35.000/M cm
-545 nm: 19.000/M cm
SuperSensintizers
Intermediate design: HMECS + HS
Extintion Coefficient
=
Thickness of Semiconductor
=
Open-Circuit Voltage
+
Fill Factor
Outlook
-Ordered oxide mesostructures in SC.
-Control on the interfacial charge recombination dynamics
Where is the future?
Js.c:
Vo.c:
-Extending light response to NIR.
Why insist in DSSC?
Excellent performance in diffuse light conditions.
Light stability.
Economically fertile field.
Conversion Efficiencies:
- Single Junction=10%
- Tandem Cells=15%
Introduction
Prof. Grätzel: nanoporous films into dye-derived wideband semiconductor.
DSC's: High efficiency, Potential low-cost, Simple assemble.
Great scientific boom: First demonstration of 10% efficiency SC by Grätzel certified by NREL (National Renewable Energy Laboratory-U.S. Department of Energy).
Structure and Operating Principle
Components
Mechanism
Energy Gain
Possible Losses
Semiconductor Film Electrode
Dye Sensitizer
Function
Why TiO2?
Aims in 'i+R+D'
Carrier for the monolayers of the sensitizer using their high surface area
Medium of electron transfer to the conducting substrate
TiO2, ZnO, SnO2, Nb2O5...
Low Price
Abundance in market and nature
Nontoxicity
Biocompatibility
Inhibite Recombination
Flexible Substrates
Large-scale
How to... TiO2?
Films on:
conducting glass
metal foil
flexible polymer
Films deposition:
"doctor Blade"

screen-printing
Colloidal TiO2 dispersions:
sol-gel method
high energy milling
Tandem Cells
Multilayer Microstructure
Light Scattering Particles
Lightweight & thickness!!
BUT: It is not possible to sinterize TiO2 on polymer substrates...
Powder compression:
-FF: 47%
-CE: 3,0%
Electrophoresis:
-FF: 61%
-CE: 4,1%
Pre-sintering:
-FF: 68%
-CE: 5,8%
Grätzel:
-Ti-metal foil for photoanode
-Pt-electrodeposited counterlectrode on ITO-PEN
-CE: 7,2%
Different band-gaps for the semiconductor:
-Nb2O5, ZnO...
Spacer Units between oxidized dye and SC
Surface pasivation of SC:
-metal oxides and insulating polymers.
-Increase FF and Voc
-Reduce Jsc...
Ideal Sensitizer:
Absorb all light below 920 nm
Adsorb firmly on SC surface
Quantum Yield = 1
Certain RedOx potential: regenerate rapidly from the electrolyte.
100.000.000 RedOx Cycles: 20 years of exposure to natural light.
Coumarin Dyes=N719
Grätzel-2006
Inorganic Dyes
Organic Dyes
Metal complexes of Ru and Os.
Quantum dots
Metal porphyrin
Phtalocyanines

High thermal and chemical stability
Natural and synthetic

Easily design of MEC
Low cost
Electrolyte
Liquid
Organic Solvent
Ionic Liquid
Quasi-Solid
Solid
Summary
Characteristics:
low viscosity
fast ion diffusion
high efficiency
easy to be designed
high pervasion into nanocrystalline film electrode
The composition of the electrolytes includes:
organic solvent:


redox couple:



additive:
nitriles: as acetonitrile, valeronitrile, 3-methoxypropionitrile
esters: as ethylene carbonate (EC), propylene carbonate (PC)
I3−/I−
SCN−/(SCN)2
SeCN−/(SeCN)2
Alkyl imidazolium cation (counter-ion) may be adsorbed on semiconductor to form a DL, which restricted the contact of I3- and semiconductor, so recombination is suppresed.
4-tert-butylpyridine (TBP) andN-methylbenzimidazole (NMBI).

Suppress the dark current and improve the photoelectric conversion efficiency.

TBP reduce the recombination through the coordination between N atom and the Ti ion in incomplete coordination state on the surface of TiO2 film.
Disadvantages:
less long-term stability
difficulty in robust sealing
leakage of electrolyte due to the volatility of organic solvent.
Advantages:
good chemical and thermal stability
negligible vapor pressure
nonflammability
high solubility for organic or inorganic materials
wide electrochemical window
Developed in recent years in view of the disadvantage of organic solvent electrolyte.
Viscosity is much higher than that of organic liquid electrolyte.
Then the transport I3− in the electrolyte is very slow.
To improve the mobility of redox couple in the electrolyte, various ionic liquid with low viscosity have been developed.
p-type semiconductor or hole transporting organic materials to replace a liquid electrolyte.
to improve the long-term stability
conversion efficiencies are not comparable with those of the liquid solar cells.
It can be seen that the module efficiency is still low for practical application.
More than 11% efficiency have achieved by EPFL and Sharp Corporation in small-area DSC.
Since 1993, industrial researchers have led the way with teams from Germany, Australia, and Switzerland. Based on licenses to the core patents held by EPFL
Sharp Corporation and Arakawa group reported 6.3% (efficient area: 26.5 cm2, confirmed, 6.3% for 101 cm2) and 8.4% (100 cm2) conversion efficiency for DSC modules.
Gifu University (Japan) developed colorful plastic solar cells with the efficiency of 5.6% based on organic indoline dye and electrodeposited nanocrystalline ZnO film electrode.
Toin University of Yokohama (Japan) has achieved more than 6%conversion efficiency on full flexible solar cells based on low-temperature TiO2 electrode preparation technology.
There are more than 30 groups engaged in the research of DSC. The research involved the dye sensitizers, nanocrystalline semiconductor film, electrolyte, counter electrode, substrate and theoretical research of interface transport, and so forth.
Later in the decade, electrophotochromic windows should be commercialized.
M. GRÄTZEL
S. DAI
FASHION!!
REVIEWS
Introduction
Energy Challenge
Replace of fossil fuels
Increasing population
Developing Countries (?)
Photovoltaics Positioning
Inorganic:
Commercially avalailable
High energy consumption for fabrication
Materials: toxic and low availability in nature (Cd, Te...)
Effiencies: long way behind "organics"
1) Light absorption
2) Exciton formation
3) Charge injection
4) Charge transport and extraction
Polypiridyl Complexes of Ruthenium
Conversion yield
Long term stability
Carboxylate Groups
Inmobilization to substrates via ester linkages
Enhave VIS light absorption
-NCS Groups
Protonation:
Surface dipole due to proton transfer
Enhace adsorption
Higher Photocurrents

Positive shift of conduction band edge
Lower Vo.c.
Inhibition of activity of polarized water molecules near S.C. substrate
"gel-like" network of aliphatic chains covering S.C. from electrolite
To improve the paradigm: red absorption
N3
Methoxy Groups:
Extended π-conjugation
LUMO fine tuning
Solar Cell + Dye
In chemistry, a conjugated system is a system of connected p-orbitals with delocalized electrons
The developing countries should not inhibit the increase in energy consumption.

These are the countries with high consumption who must rethink their models.
¡No!
Leading authors
Leading Institutions
Leading journals
Leading journals
Most cited topics for "Solar Cell"
(good!)
(bad!)
thanks for your attention
!
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