Jörg Ackermann

Centre Interdisciplinaire de Nanoscience de Marseille (CINAM)CNRS - UPR 3118, MARSEILLE - France

1

Development of active inks for organic

photovoltaics:

state-of-the-art and perspectives

Genes’Ink, avenue Gaston Imbert, 13106 ROUSSET Cedex, France

Outline

• Overview on important parameters for large scale robust printed OPV production

• Inorganic nanoparticle inks for

– ITO replacement

– Electron transport layer

– Active layer: fullerene replacement

• Conclusion

2

Printed plastic solar cells: low cost production and new features

Flexible substrates

Roll-to-roll or sheet to sheet

3

Printed Plastic Photovoltaics

New features:

Flexibility

Light weight

Transparency and colorin combination with

low cost production

4

Strong progress in OPV, now over 10% efficiences

Challenges for printed large areas low cost efficient OPV

What’s still to do?

• Solar energy conversion efficiency? 10% is already high

but on small areas under N2 atmosphere, not printed

• Low cost, robust and stable materials compatible with low temperature

processing in air

•Printing = robust, reliable deposition technology

need of materials for thick layers processing ( 200 nm or better more)

• ITO replacement important for flexibility and price reduction

5

Substrate (PET)

Electrode (transparent)

Electron transport layer (ETL)

Active layer

Hole transport layer (HTL)

Electrode (A)

Device structure of an inverted solar cell

6

-

_

_-

_+

Substrate (PET)

Electrode (transparent)

Electron transport layer (ETL)

Active layer

Hole transport layer (HTL)

Electrode (A)

Inorganic nanoparticles for printed polymer solar cells

7

Challenges for ITO replacement

8

Substrate (PET)

Electrode (transparent)

Electron transport layer (ETL)

Active layer

Hole transport layer (HTL)

Electrode (A)

Economic assessment of ITO-free electrodes for organic

solar cells

Emmott C. J. M, et al Solar Energy Materials & Solar Cells 97 (2012) 14–21

9

Ag Nanowires for ITO replacement

Challenges: roughness of layers, conductivity, printing limited by size

10

.Ag Nanowires for ITO replacement at CINaM

Variation of

length and diameter

11

Diameter down to 30 nm

Length 3-5 μm

Drop casting

Spin-coating

Optical properties of Ag NW films

12

Conductivity measurements under work

Example inverted structure

13

Substrate (PET)

Electrode (transparent)

Electron transport layer ETL

Active layer

Hole transport layer (HTL)

Electrode (A)

Electron Transport Layer (ETL)

Electron Transport Layer (ETL)

AZO film need processing at 260° C for 10 min

T. Stubhan et al. / Organic Electronics 12 (2011) 1539–1543

Solution processed Al doped ZnO (AZO) films

for robust thick ETL layer processing

Doped ZnO nanoparticles needed for low temperature processing

15

Al doped ZnO nanoparticles for low temperature processing

AZO nanoparticle up to 1.4% Al doping,

Size 10-20 nm

16

17

Hybrid bulk heterojunctions

Substrate (PET)

Electrode (transparent)

Electron transporting layer ETL

Active layer

Hole transporting layer (HTL)

Electrode (A)

+

Adv. Funct. Mater. 2005, 15, 1617–1622.

18

+

Standard solution processed OPV

P3HT PCBM

500 nm

TEM

18

+

Adv. Funct. Mater. 2005, 15, 1617–1622.

Still challenges for industrial use:

Thermal and electronic stability in air,

19

+

Standard solution processed OPV

P3HT PCBM

500 nm

TEM

19

Thermal instability

• Nanoparticles as

fullerenes

substitutes;

• Expected

advantages:

– improved air

stability;

– Improved

morphology stability;

– Improved e- mobility 20

Hybrid BHJ based OPV

+Inorganic acceptors:- Nanocrystals;- Nanorods;- Tetrapods;- …

* Zhou et al. 2008

Standard BHJ based OPVHybrid BHJ based OPV

20

Hybrid CdSe-P3HT solar cells

Alivisatos et col. Science 295 (2002)

CdSe Nanorods lead to additional light absorption,

Alivisatos et col. Nanoletters 7 (2007),409

CdSe tetrapods result in better charge transportbest efficiency of 2.8 % with P3HT.

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WR at 3.2 % with low band polymer PCP-DBTBT and

CdSe*

*Smita Dayal , et al Nano Lett. 2010, 10, 239-242

High band gap semiconductors, thus no light absorption

in the visible, but non toxic, cheap abundant materials

= 0.8% - 2.2 % using P3HT

R. Janssen et al. Adv. Mater 16 (2004), 1009

Hybrid solar cells using metal oxide nanoparticle as

acceptor: ZnO and TiO2 nanoparticles

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ITO/PEDOT:PSS/P3HT:PCBM

P3HT:ZnO better thermal stability compared to P3HT:PCBM

23

ITO/PEDOT:PSS/P3HT:ZnO

Morphological stability under temperature stress

Organic solar cells using inorganic acceptors :

where are we now ?

J. of Colloid and Interface Science 369 (2012) 1–15

How to increase efficiency of HPV:

use of new low bandgap polymers, interface and morphology control

Efficiency of hybrid approaches

still lower than all organic PV,

But have potential for better

morphological and electronic stability

Interface control is important

�

27

Synthesis of 3D metal oxide nanoparticles

Improved charge transport,

reduced number of nanoparticle

interfaces

28

400 500 6000,0

0,5

1,0

1,5

2,0

Ab

sorb

an

ce (

a.u

.)

Wavelength (nm)

ex 310nm

0

2

4

6

PL

inte

nsity (a

.u.)

500 nm

380 nm

Synthesis of 3D metal oxyde nanoparticles

SFUMATO - 28/09/2012 (Marseille)

ZnO tetrapods

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Core 15 nmBranches 20 nm

Residual Ligands (C18 : isolant)

Conclusions

• ITO replacement has many alternatives, Ag

nanowires may be most suitable

• Cheap, stable and efficient conductive and

hole and electron extracting inks based on

inorganic (hybrid) nanoparticles are ready for

production of OPV.

• Use of inorganic acceptors to replace

fullerenes in the bulk heterojunction still 30

Thank you for your attention