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Optimisation de la collecte de lumière et de charges dans les
cellules solaires à colorant à base de ZnO.
Thierry Pauporté, Constance Magne, Victoire-Marie Guérin
Laboratoire d’Electrochimie, Chimie des Interfaces et Modélisation pour l’Energie.UMR-CNRS 7575, Ecole Nationale Supérieure de Chimie de Paris,
11 rue P. et M. Curie, 75231 Paris cedex 05, [email protected]
JNPV 2012, Chantilly, le 14 décembre 2012
ZnO and Photovoltaics
• 2nd generation : • Thin Film solar cells (CIGS, a-Si).
• New generation• Nanostructured oxide p/n junctions.
• Cathode buffer layer (OPV)
• ETA cells
• Quantum dots sol. Cells
• Dye-sensitized solar cells (DSSCs)
3 33
Dye-sensitized solar cells (DSSCs)
Solar cell structure
n Adjustable parameters : v dyev electrolytev semiconductor
n TiO2, ZnO.
n-SC
Photoelectrode functionning
Excitation
Injection
Transportτtr
Dye
Semi-conductor
Verre FTO
I3-
Recombinationτrec
τtr : transport timeτrec : electron lifetime before recombination
ECB
( ) collinjLHE η×η×η=λη
Light Harvesting Efficiency (LHE)
Excitation
DyeZnO Semi-conductor
Verre FTO
High dye loading → High roughness
ZnO versus TiO2 ?
• ZnO as an alternative to TiO2– Same bandgap and electronic affinity as TiO2– Higher electron mobility than TiO2
• Better electron transport?
– Synthesis at low temperature– Various morphologies
• Preferential pathway for e-?
6
I– Collecte des électrons.
7
Study by Electrochemical Impedance Spectroscopy (EIS):
- Large frequency range.- Large voltage range.- In the dark and under light.
Sous presse
NP-ZnO
Full equivalent electrical circuit
RctCμ
Rtr
RctCμ
Rtr
RctCμ
Rtr
RctCμ
RtrRtrRS
RBLZd
RPt
CPt
FTO ZnOFTO + Pt
Electrolyte
CBL
Diffusion/recombinaison of electrons in ZnO
Electron transfer at the CE
Ions diffusion in the electrolyte
Ions diffusion in the electrolyteElectron transfer at the CE
Diffusion/recombinaison of electrons in ZnO
9Rs
Measured physical constants
Charge transfer resistance
Rct
Chemical capacitance
Cµ
Transport resistance
Rtr
Electron lifetimeτn = RctCµ
Electron transport time
τd = RtrCµ
10
All cases τn >>τd
Lifetime τnTransport time τd
11J. Mater. Chem. A, DOI:10.1039/C2TA00674J.
Electrodeposited nanoporous versus Nanoparticle ZnO films
12C. Magne, T. Pauporté et al. J. Mater. Chem. A, (2012)DOI:10.1039/C2TA00674J
Conductivity:
Rendement de collection de charges:
ZnO
n
trcollection
1
1
ττ+
=η
trn RpA
L)1( −
=σ
II-Limitation des recombinaisons.
13
Système classique : acide cholique
Exemple :Y. Sakuragi et al. J. Photochem. Photobiol. A: Chemistry 216 (2010) 1–7
Rôle du co-adsorbant dans la sensibilisation par des molécules organiques
Fatty acid co-adsorbants
Acide Formulae Structure length (Å)
Dyeloading (mol.L-1)
None 0 0.205
Butyric C4H8O2 5.9 0.254
Octanoic C8H16O2 10.9 0.149
Lauric C12H24O2 16.1 0.119
Stearic C18H36O2 23.7 0.085
Cholic C24H40O5 15.6 0.106
15C. Magne, T. Pauporté et al., RSC Advances, 2 (2012) 11836–11842.
Co-adorbant VOC (V) JSC (mA.cm-2) FF (%) η (%)
No acid 0.55 8.4 75 3.46butyric acid 0.58 10.1 73 4.22
Octanoic acid 0.57 11.8 70 4.73Lauric acid 0.57 8.6 74 3.61Stéaric acid 0.58 5.3 64 1.97Cholic acid 0.61 8.8 73 3.89
Under light In the dark
Acid length
16
Acid co-adsorption : cell performances
C. Magne, T. Pauporté et al. RSC Advances, 2 (2012) 11836–11842.
• Autre effet :
Stabilité de la cellule au vieillissement.(Voir article)
C. Magne, T. Pauporté et al. RSC Advances, 2 (2012) 11836–11842.
III-Optimisation de la collecte de lumière.
18
Optimisation de la collecte de lumière
i. Surface spécifique.
ii. Design du colorant.
iii. Co-sensibilisation par plusieurs colorants.
iv. Piégeage de la lumière : Structures diffusantes.
Which dye for ZnO-based DSSC?
Eosin Y
N719
D131
D149 D205D102
300 400 500 600 7000
1
λ (nm)
Abs
orba
nce
Absorbance of dyes in solution
20Guérin VM., T. Pauporté. et al. ACS Appl. Mater 2 (2010) 3677-3685
• Recently
Strongly electron-withdrawing dicyanovinylidene
DN350 : η=5,5% → +10% / D205
New Benzothiadiazole dye (RL1)
η = 5,8 % → +10% / D149
Lin et al.Chem. Commun., 2012, 48, 12071–12073
Use of dye mixtures
1-T of the sensitized ZnO films
22
Cocktail approach
Constance Magne and Thierry Pauporté, submitted
( )photonsincident
producedélectrons
n
nIPCE =λ
23
Light confinement
Increase of the light pathway in the photoelectrode
Particle DSSC films
TiO2 → η +10%/withoutS. Ito et al. Thin Solid Films 516 (2008) 4613–4619
Angew. Chem. Int. Ed, 2008, 47, 2402-2406
Nanoparticle aggregates
University of Washington, Seattle
ZnO Nanowires on FTO
ZnO Micro-urchinon FTO
Coll. EMPA, Thun, Switzerland. Adv. Mater. 2010, 22, 1607
Nanowires organized in a 3D network
→ ZnO nanowire based system
300 400 500 600 700 80005
101520253035404550
(d)(c)
(b)
(a)
R /
%
λ / nm
Urchins = scattering layers
Light scattering → Better light collection in the orange-red WL region
Light conversion quantum efficiency
V.M. Guérin, Th. Pauporté, J. Elias, Phys. Chem. Chem. Phys. 14 (2012) 12948–12955.
NW
Mono-Ur
Multi-Ur
NW
Mono-Ur
ZnO Micro-Urchin based DSSC
Conclusions
ZnO DSSC :• ηcoll élevé dans ZnO (→ σn).• LHE reste à améliorer.
-Études sur DSSC TiO2
Remerciements :- Saint-Gobain Recherche- ANR Asyscol (Habisol) 2009-2012
• Density of states:
28
Cµ is due to bandgap states localized below the conduction band edge.
DOS measured from Cµ versus V Deduced energy diagram
J. Mater. Chem. A, DOI:10.1039/C2TA00674J.
( )p1qSLC
DOS−
= µ
