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Dye-sensitized Solar Cells: Options, Problems, and Inspirations for Water Treatment

F. Marlow El Gouna, Febr. 2015

MPI für KohlenforschungMülheim an der Ruhr

• 1914• Fischer-Tropsch• Ziegler-Natter• Coffein extract.• Now: Catalysis• Porous materials

Outline

� Options

� Problems I: Practical realization

� Problems II: Understanding

� Inspirations for water treatment

V

A- +

Operation principle

Fig. from Carp et al.

work

2

The solar cell research field

Options

Up to 12%

< 10 $/m²

Environmental-

friendly

Simple fabrication

Small-scale

fabrication possible

No technology

barrier

No financial barrier

Low weight

Decorative

Tandems possible

FhG-ISE

Wikipedia

3

Problems I: Practical realization

� Top values difficult to realize (often 6%)

� Fluctuations in efficiency (in a cell, cell-to-cell)

� Fluctuations in lifetime

� Size dependence

� Electrolyte dependence (3 ions, additives, solvent)

� Most works use glass supports

All these have influence on applications!

Hinsch 2012 (Fraunhofer ISE):

12% on < 1 cm² (EPEL, 2011)

11% on 1 cm² (Sharp)

8 % on 18 cm² (Sony)

5 % on 100 cm² (FhG-ISE 2012)

Our DSSC projects

Improved DSSC anodes

Time-resolved characterization - ∆J(t)

Improved theoretical understanding

Reliable fabrication(reproducibility, stability)

I-

Photon management(A. Khalil, S. Abdellatif)

Changed composition-> ECB -> Voc

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Problems II: Understanding

Current research work:

Is the Charge Transport in Dye-sensitized Solar Cells

really understood?

F. Marlow, A. Hullermann, L. Messmer, Adv. Mater. (2015) in press.

Measurement

of transients

Barnes/J/Grätzel/O‘Regan 2013

Review42 pages

ca.100 physical parameters144 references

Charge transport

Electrical response behavior

Responseafter a laser

pulse

t

J

??

Current theoretical background: The standard modelThree basic assumptions: (1)The transient effects can be ascribed to field-free electron diffusion. (2)The signal is associated with the photo-e- reaching the outer contacts. (3)The diffusion is heavily modified by the interaction with e- trap states.

Barnes, Miettunen, Li, Anderson, Bessho, Grätzel, O'Regan, Adv. Mater. 2013, 25, 1881-1922

V

A- +

Parameters+

Interpretations

Sens | I3- ↔ I- + 2e- | FTO

Mo

de

l

5

Experimental details

� „Standard“ (?)

� Laser: 8 ns

� Effective detection resolution: 1 µs

� Blind time:4 µs

� Test withSi-SC:Reaction timebelow 20 µs

� DSSC electrolyte:based on ethylene glycol

Figure from A. Hullermann, MSc-Thesis 2014.

Laser unit: Flash lamps +power supply

F2

F1Results: The J-transients

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Dependence on external parameters

A closer look at the voltage dependence J

F3

Pulseelectrons

Steady-state electrons

Basics: JV curves

V

J

Jsc

Voc

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Dependence on internal parameters

F4

Discussion

NCB = α ln(1+β Nhν) Nhν - number of absorbed photons

• Model:Φ1 = k1 Nnss

Φ2 = k2 Nnss

Φ3 = k3 (Nnss)2

• Internal interface voltage:Uii = UP + J0RS+

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Conclusions from J-transients

� F1-F4: Contradictions to the current interpretation.

F1: Delay

F2: √t rise

F3: U-effects

F4: No Einstein relation:

tchar ≠ 1/D (dchar)2

� No easy repair possibility

� Direct field effects on charge transport (likely)

� Nonlinear recombination channel (likely)

� There is diffusion. But: What exactly is diffusing?

=> Open:

� Determination of D

� More rational design

(1)J field-free electron diffusion(2)J e- at outer contacts(3)J trap states

?

What is really happened after laser excitation?

Formation of an internally charged BHJ

Primary charge separation

De-charging of the ic-BHJ

� fs J ps

� No current response

� ns J µs (?)

� „Regeneration“

� No current response

� µs J ms

� Simultaneous escape of both charges only

� Measurable current

I-

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Inspirations

High quantum Low quantum

efficiency efficiency

I-

e-

h+

e-

h+

A

A‘

B‘

B

Solar energy Photochemistry

for electricity - environmental (Air, water!!)

- synthesis

(3 problems!)

TiO2

Not very successful

TiO2

DSSC-inspired hypothetical solution

e-e-

A

A‘

B‘

B

Interesting example:

B = OH-

B’ = HO•

e-

C C‘

h+

C = hydrocarbons

C’ = J

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Project outline

Idea: new typeof photocatalyst

Proof of principle

Adaptation to a emulsion or droplet

system

Application example

Image of a macroscopic droplet system(J. Akilavasan et al.).

2 years

1 year

Summary

� Options� 12 % without high-tech + J

� Problems I: Practical realization

� Problems II: Understanding� Need for a new model

� Open measurement problem for D

� “New” rational design possible?

� Inspirations for water treatment� Cooperation?

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Thanks

Abigail Hullermann

Lisanne Messmer

Parvin Sharifi

J. Akilasavan, R. Goddard, D. Kasper, G. Mane, M. Mischner, D. Naumann, E. Samsonova, F. Schüth, D. Rainko, S. Wall

A. Khalil

RESOLVRUHR EXPLORES SOLVATION

CLUSTER OF EXCELLENCE - EXC 1069

IMPRS-SurMat

NanoScape

Thank You !