1938-11 workshop on nanoscience for solar energy conversion · bolink chem. phys. lett. 46557–62...

1938-11

Workshop on Nanoscience for Solar Energy Conversion

Juan BISQUERT

27 - 29 October 2008

Departament de Fisica, Universitat Jaume 1Avda. Sos Baynata sn 12071 Castello de la Plana

Spain

Impedance Spectroscopy of Nanostructured Dye-Sensitized and Organic BulkHeterojunction Solar Cells

Impedance spectroscopy of nanostructured dye‐sensitized and organic bulk heterojunction solar cells

Juan Bisquert

Departament de Física

Universitat Jaume I

12071 Castelló

Spain

Trieste, Italia, 28 october 2008

Fundamental model of a solar cell

Fundamental model for a solar cell

J. Bisquert, D. Cahen, G. Hodes, S. Rühle, A. ZabanJournal of Physical Chemistry B, 108, 8106-8118 (2004)

1. Generation

2. Recombination(radiative)

3. Extraction

The necessary spatial extensionof the light absorbing material makes it necessary to considerelectron diffusion

Diffusion competes withrecombination as described by diffusion length

Fundamental impedance model for a solar cell


Recombination resistance isunavoidable. Prevents the internalloss of photogenerated carriers

Chemical capacitanceconverts excess carriersnumber into a potential(Fermi level)

Diffusion‐recombination transmission line model

Diffusion‐recombination transmission line model

J. Bisquert, J. Phys. Chem. B 106, 325-333 (2002) F. Fabregat-Santiago, J. Bisquert, G. Garcia-Belmonte, G. Boschloo, A. Hagfeldt Solar En. Mat. Sol.Cells, 87, 117-131 (2005).

Impedance spectroscopy gives allparameters of electronicprocesses at once:ConductivityChemical capacitanceRecombination resistance

Transmission line for diffusion‐recombination

chemical capacitance

recombination

transport

Transmission line for diffusion‐recombination

Diffusioncoefficient

Electron Lifetime

LD much longer than thickness(low recombination)

( ) ( )[ ]2/12/12/1

/i+1/coth/i+1 kdkkkW RRZ ωωωωωω ⎟

⎟⎠

⎞⎜⎜⎝

⎛=

Silicon solar cell

Lifetime τ = Rrec Cμ

Silicon solar cell

Lifetime

Chemical capacitance

Recombination resistance

Some results on dye‐sensitized solar cells withdifferent hole conductors with impedancespectroscopy

Impedance of 11% efficiency dye solar cell

This solar cell shows ideal characteristic of diffusion-recombination modelwith recombinationresistance much largerthan transport resistanceR3 >> R1

Recombination arc R3 Diffusion WarburgR1/3

Michael Grätzel, Francisco Fabregat-Santiago, Juan Bisquert et al.,

J. Phys. Chem. B. 110, 25210-25221 (2006)

Electron diffusion coefficient

Parameters of 11% DSC

Temperature dependence ofelectron diffusion coefficient in a DSC, as a function ofpotential

This data concordates with theprediction of the multipletrapping model

Michael Grätzel, Francisco Fabregat-Santiago, Juan Bisquert et al.,

J. Phys. Chem. B. 110, 25210-25221 (2006)

)(

2

μCRLDt

n =

Impedance characteristics of DSCs

DSC with ionic liquid

Ion diffusion in electrolyte

Electron recombination

Charge transfer at CE

Stability

Upscaling

Steady‐state characteristics of 11% DSC

Photocurrent-voltage curve of 11% efficiency DSC obtained at AM 1.5 solar radiation.

The dots show the calculated values based on impedance measurements carried out at different voltage bias of the cell with the same illumination.

Dashed line represents the simulated curve after subtraction of the series resistance contribution. A 10 % increase in the fill factor is obtained.

F. Fabregat-Santiago, J. Bisquert et al JPCC (2007), 111, 6550F. Fabregat-Santiago, M. Grätzel, J. Bisquert et al (2008), submited

DSC cell with spiro‐OMeTAD as hole conductor


LrR tt =

)1( pSRL

t −=σ

⎥⎦⎤

⎢⎣⎡ −=

kTEE cbFnexp0σσ

neμσ =

Conductivity in TiOConductivity in TiO22


Chemical diffusion coefficient of electrons in TiO2

⎥⎦⎤

⎢⎣⎡ −−= )()1(exp0 cbFnn EEkT

DD β

Lifetime

μτ CRctn =Voc decayVoc decay

A. Zaban et al. ChemPhysChem, 4 (2004) 859F. Fabregat-Santiago et al. J. App. Phys. 100 (2006) 034510

Potential (V)

0.60.40.20.0

τ (s

)

0.001

0.01

0.1

1

10

100OMeTADliquid

DSC cell with spiro-OMeTAD as hole conductor

1

dd −

⎥⎦⎤

⎢⎣⎡=

tV

kTe oc

decayτ

Diffusion length of electronsnD DL τ=

DSC cell with spiro-OMeTAD as hole conductor

Evolution of DSC at UJI

DSC record laboratorio UJI:7.2% eficiencia referencia con N719

Área 0.3 cm2

Evolución Eficiencias DSC en la UJI

Tiempo (meses)

Julio 07 Sept 07 Nov 07 Febr 08 Mayo 08 Julio 08

Efic

ienc

ia (%

)

1

2

3

4

5

6

7

8

CdSe quantum dot sensitized SC

Ivan Mora-Seró

Universidad de AlicanteRoberto GómezTeresa Lana

CdSe quantum dot sensitized SC

3 electrodes measurements

Closed cell

⎥⎦

⎤⎢⎣

⎡⎟⎠⎞

⎜⎝⎛ −

−−−⎟

⎠⎞

⎜⎝⎛ −= )()1(exp)(exp0 refref VVkT

eVVkT

ejj αα

j0 (Polysulfide) = 11.4 nA/cm2

j0 (I3-/I- ) = 40.7 μA/cm2

Impedance spectroscopy of P3HT:PCBM organic solar cell

The standard model – the pin model

The pin model for amorphous Si

Results of impedance on P3HT:PCBM solar cells

Henk J. Bolink, Michele Sessolo, Alejandra Soriano (ICMol Valencia)

Juan Bisquert, Germà Garcia-Belmonte, Antoni Munar

Irati Ugarte, Roberto Pacios

Characteristics of P3HT:PCBM solar cell

G. Garcia-Belmonte, A. Munar, E. M. Barea, J. Bisquert, I. Ugarte, R. Pacios Organic Electronics 9, 847-851 (2008)

Diffusion-recombination of electrons (minority carrier

Schottky barrier

Impedance measurements in the dark varying forward bias ITO/PEDOT:PSS/P3HT:PCBM/Al

ITO/PEDOT:PSS/P3HT:PCBM/Al


Bias voltage (V)

0.2 0.4 0.6 0.8 1.0

Ele

ctro

n m

obilit

y (1

0 -3

cm

2 V-1

s-1

)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

illuminationdark

~2×10-3 cm2 V-1 s-1TkeD Bnn /=μ

V. D. Mihailetchi et al. Avd. Funct. Mater. 13, 43-46 (2003)

Doping of P3HT‐Schottky barrier

Oxidation of P3HTp-doping level ~5×1016 cm-3

Minority carrier storage (electrons)


M. S. A. Abdou et al. J. Am. Chem. Soc., 119, (1997)

Forward bias

Shift of Mott‐Schottky plot

Forward bias

J. Bisquert, G. Garcia‐Belmonte, A. Munar, A Soriano, M. Sessolo, H. J. Bolink Chem. Phys. Lett. 465 57–62 (2008)

Shift of Mott‐Schottky plot

Kelly-MemmingJ. Electrochem. Soc. 75, 085316 (1982)

Kinetic limitation

J. Li and L.M. Peter, J. Electroanal. Chem. 193 (1985) 27.

Photovoltaic model

F. El Guibaly, K. Colbow and B.L. Funt, J. Appl. Phys. 52 (1981) 3480.

Negative capacitance in solar cells

I. Mora-Seró, J. Bisquert, et al. Nano Letters 6, 640, (2006)

CdS/CdTe solar cell

Forward bias

Model of electron injection in organic LEDs

J. Bisquert, G. Garcia-Belmonte, A. Pitarch, H. J. Bolink, Chem. Phys. Lett. 422, 184 (2006)

1.Equilibrium

2.Equibrium between metal and surface state

3. Decrease of the occupation of the intermediate state at increasing forward bias due to higher kinetics of transfer at higher forward bias

movie

Glass substrate

ITO

PEDOT

LEP (Super Yellow)

cathode

0 / 200 nm

80 / 150 nm

100 nm

*

OCH3

OCH3

*

OC4H9

OC4H9

OC4H9

OC4H9

x

y

zn

Bias voltage [V]

0 1 2 3 4 5 6

Cur

rent

den

sity

[A c

m-2

]

10-8

10-7

10-6

10-5

10-4

10-3

10-2

AuAg

Mg

Frequency [Hz]

100 101 102 103 104 105

Abs

(Cap

acita

nce)

[F c

m-2

]10-9

10-8

10-7

10-6 1.0 V2.0 V3.0 V3.6 V 4.0 V4.6 V

(b) Geometric Capacitance+ SCLC

Interface states: transit from positive to negative capacitance

ITO/PEDOT:PSS/SY/Al

Negative capacitance in OLEDs

Model


Model

θqNVCVC Iscscdd =−

020

2

2=

Φ+

−−

∂

∂ − xnn

eDL

nnxn αα

{ }BAkNJ I θθ −−= )1(1212{ }HnCNkNJ cI )1)(0(2323 θθ −−=

( )1)()0( −Φ+= − wnn ewJJ α

Electrostatic at the interface

Generation, recombination, diffusion in neutral region, collection in scr

Transference through ss

Model

Ln

TkqVn

I

n

n

L

gTkqV

n

nc

In

yDHeL

kN

LnD

yJ

HeDLCN

kNJBsc

Bsc

tanh)1(

1

tanh)1(

)0( /23

0/

23θ

θ

−+

⎟⎟⎠

⎞⎜⎜⎝

⎛+−−

=

⎥⎥⎦

⎤

⎢⎢⎣

⎡⎟⎟⎠

⎞⎜⎜⎝

⎛−−

−+−Φ= −−

−− ww

LnL

L

n

nwg eeyLy

eL

LeJ αα

αα

αα

αtanh1

cosh11

22

22

The solution of the model provides the following expression for the photocurrent

This allows to determine ss occupancy and therefore, the distribution of potential and Fermi level at the interface

Potential in space charge region and dipole layer

Voltage = 0

EFn

- 4 - 2 0 2 4

- 0.4

- 0.2

0.0

0.2

0.4

position

volta

geEFn

Voltage = 0.1- 4 - 2 0 2 4

- 0.4

- 0.2

0.0

0.2

0.4

position

volta

ge

Voltage = - 0.1

EFn

- 4 - 2 0 2 4

- 0.4

- 0.2

0.0

0.2

0.4

position

volta

ge

dark

light

Model simulation of current-potential curve

dark

light

Shift of Mott-Schottky plot

dark

light

: The total density (per unit area) of interfacial levels [1012 cm-2]

Electron density in equilibrium [10^12 cm-3]


Acknowledgments

Funding:MCINN, ESF, Fundació Caixa Castelló Bancaixa

Homepage: www.elp.uji.es/jb.htm

E‐mail: [email protected]

Acknowledgments

www.hopvconference.org

1938-11 workshop on nanoscience for solar energy conversion · bolink chem. phys. lett. 46557–62...

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