Optimisation de la collecte de lumière et de charges dans les...

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, France.thierry-pauporte@chimie-paristech.fr

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