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Lund University Chemical Physics Department

Villy Sundström

Dye sensitized Perovskite e-

Catalyst

Charge Carrier Dynamics of Nanostructured Solar Cell Materials Studied by Time-

Resolved THz Spectroscopy

10 5

10 6

10 7

10 8

10 9

10 10

10 13

10 14

10 15

10 16

10 17

10 18

10 19

Frequency (Hz)

Region Radio & TV Microwaves Infrared UV RTG

10 20

THz

10 1 2

Visible

11 10

Our Energy Use

Problems!

The consequences CO2 Temp

Havsnivån

Global temperaturfördelning

IPCC report 2013

Solar energy – no CO2 FUEL - Hydrogen FUEL

HEAT - solar cooker

Solar tower

Heliostats

HEAT

Photosynthesis - biomass ELECTRICITY

Organo metal perovskites

SOLAR CELLS

Plastic Dye sensitized

PLASTIC SOLAR CELLS

PCBM

NN

S

S Sn

R R'

LBPF7 = DiH, R=R'=C6H13 (hexyl)LBPF1 = HEH, R=C6H13 (hexyl) R'=CH2CH(C2H5)C4H9 (2-ethylhexyl)LBPF5 = DiO, R=R'=C8H17 (octyl)LBPF6 =DiD, R=R'= C12H25 (dodecyl)

APFO3 ITO Al

• LIGHT ABSORPTION

• ENERGY TRANSFER

• CHARGE GENERATION

• CHARGE SEPARATION

• FORMATION OF MOBILE CHARGES

• CHARGE RECOMBINATION

• CHARGE TRANSPORT

• CHARGE EXTRACTION

Viewing electrons at work – Terahertz

spectroscopy 10

5 10

6 10

7 10

8 10

9 10

10 10

13 10

14 10

15 10

16 10

17 10

18 10

19 Frequency

(Hz)

Region Radio & TV Microwaves Infrared UV RTG

10 20

THz

10 1 2

Visible

11 10

1 THz = 1 ps = 0.3 mm = 33 cm–1 = 4.1 meV = 48 K

Carlito Ponseca

Time-domain terahertz spectroscopy

Emitter Sample

THz pulse

Sensor

Optical pump pulse

-3 -2 -1 0 1 2

Time (ps)

1.2

0.8

0.4

0

-0.4

-0.8

-1.2

Ele

ctr

ic f

ield

(a.u

.)

Transmitted THz pulses

Ground state

Excited state

Difference

• Measure shape of the E-field • Amplitude + Phase info • Real + Imaginary part of conductivity • More info!

ZnTe

THz Case Studies

THz

Re

Im

Molecular exciton

THz

Free charges Re

Im

Re

Im

Confined mobile charges

THz

Re

Im

THz

Bound charges, polarons

Charge mobility in

plastic solar cells

Confined charges Mobile charges

Δ = concentration x mobility

H Nemec et al. JPC C 112 (2008) 6558; PRB 79 (2009) 245326; Phys. Rev. Lett. 104, 197401 (2010)

C. Ponseca et al. JACS 134 (2012) 11836

K. Zidek et al. JACS 134 (2012) 11836

Confined mobile charges

THz

Re

Im

NN

S

S Sn

R R'


Origin of THz response – e- or e+? Monomer/PCBM – electron mobility Polymer/PCBM – hole mobility

C. Ponseca et al. J. Phys. Chem. Lett., 3 (2012) 2442

1.5 ps

0.5 ps

+ ~ 10 x - Hole mobility increases with chain length

-

+

space,time S0

S1 + - -

+ -

h

kCT k*

CS CTn

CT0

kCS

ktransport

kextraction En

erg

y

Electrode

kBR

SC

fs – ns ns – sub-ms

CHARGE SEPARATION IN BHJ SOLAR CELLS - TREFISH

NN

S

S Sn

R R'


NN

S

S Sn

R R'


+ + +

Drift distancse

Mobility

Or Monte Carlo Simulation

CHARGE SEPARATION – TREFISH

Free charges at ~ 500 ps

S. De et al. JACS 129 (2007) 8466 S.K. Pal et al. JACS 132 (2010) 12440 D. Vithanage et al. Nature Comm. 4 (2013) 2334 V. Pranculis et al. JACS 136 (2014)11331

D ~

DYE SENSITIZED SOLAR CELLS

Electron injection

Electron recombination

e

e

Charge separation in DSC

H Nemec et al PRL 104, 197401 (2010);

J. Photochem. Photobiol. A. 215 (2010) 123

e-

e+

e-

Electron-Hole interaction

Charge separation in DSC

0 0.2 0.4 0.6 0.8 1 1.2

Frequency (THz)

1.2

0.8

0.4

0

-0.4

-0.8

-1.2

Ima

gin

ary

R

ea

l

All delays, 36 % (cut) Real, 1 ps

All delays, 36 % (cut) Real, 3.7 ps






All delays, 36 % (cut) Imaginary, 1 ps

All delays, 36 % (cut) Imaginary, 3.7 ps






-spectrum

Confined

charges

t

N

N N

N

Zn

OH

OO

OH

(c)

D

D* EC D + + e – mobile

(2)

(1)

(3)

(4)

(5) (6)

H Nemec et al PRL 104, 197401 (2010)

(t) - Mobile charge formation

0 50 100 150 200

Pump-probe delay (ps)

1

0.8

0.6

0.4

0.2

0

Sin

gal (a

rb.

units)

Ru-N3/ZnO

ZnTPP-Ipa/ZnO

Ru-N3/TiO2

ZnTPP-Ipa/TiO2

(a)

TiO2

ZnO

0 100 200 300 400 500

A (

A.U

.)

time / ps

Optical TA

TiO2, ZnO

< 5 ps Oxidized dye formed

DSSC to Perovskites Historic Evolution

From: HJ Snaith, J. Phys. Chem. Lett. 2013, 4, 3623−3630

CH3NH3

Iodide

CH3NH3PbI3

Pb

Organohalide perovskite solar cells – the issues

Organohalide Perovskite

Pb

• >15 % efficiency • Injection in P/TiO2? • P/Al2O3 higher efficiency than P/TiO2

• Also thin film P • Micrometer carrier diffusion • Exitons or free charges? • Mobility?

CH3NH3

Iodide

CH3NH3PbI3

Pb

Organohalide perovskite solar cells THz conductivity

P/TiO2 Neat P; P/Al2O3

TA

Perovskite SE

e- absorption

PL • Free charges in ps

• Injection in P/TiO2 • s recombination • Very high carrier mobility

• Balanced transport • Slow activated recombination

C. Ponseca et al. JACS 136 (2014) 5189 T.J Savenije et al . JPC Lett. 5 (2014)2189

MW conductivity

Al2O3

Al2O3

-

-

-+

+

TiO2

TiO2

+

-

-

--

-+

+

+

CONCLUSIONS

How to view charge in motion

Plastic solar cells – generation of mobile charges

From DSC to perovskite solar cells

Lund University Chemical Physics Department

Co-workers • Arkady Yartsev • Tonu Pullerits • Swati De • Suman Pal • Torbjörn Pascher • Mattias Andersson • Yingyot Infashaeng • Dimali Vithanage • Carlito Ponseca • Jens Uhlig • Wilfred Fullagar • Ujjwal Mandal • Dharma Kuruntu • Pavel Chabera • Tobias Harlang • Sophie Canton • Yizhu Liu • Kasper Kjaer • Mohamed Abdellah • Kaibo Zheng

Collaborators • Vidas Gulbinas • Olle Inganäs • Mats Andersson • Jenny Nelson • Hiroshi Imahori • Shen YE • Hynek Nemec • Nenad Vukmirović • Stenbjörn Styring • Leif Hammarström • Kenneth Wärnmark • Licheng Sun • Christian Bressler • M.M. Nielsen • Joel Ullom • Tom Savenije • Petter Persson • Lisa Fredin

lund university - photonicsweden.com sundström lund.pdf · solar cell materials studied by time-...

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