Efficient Organic Exciton

Cells with Carbon Nano

Replacing In

2

O

3:Sn

as the Transparent Elec

Jao van de Lagemaat,

† Teresa Barn

Rumbles,

† Sean Shaheen,

† Timothy 

Chris Weeks,

* Paul Glatkowski,

* Igor 

and Jorma Peltola

*

NREL/PR-520-39849Presented at the 2006 IEEE 4th World Conference on Photovoltaic Energy Conversion (W

held May 7-12, 2006 in Waikoloa, Hawaii.
Disclaimer and Government License

This work has been authored by Midwest Research Institute (MRI) under Contract No. DE-AC36Department of Energy (the “DOE”). The United States Government (the “Government”) retains athe work for publication, acknowledges that the Government retains a non-exclusive, paid-up, irrepublish or reproduce the published form of this work, or allow others to do so, for Government puNeither MRI, the DOE, the Government, nor any other agency thereof, nor any of their employeeor implied, or assumes any liability or responsibility for the accuracy, completeness, or usefulnesproduct, or process disclosed, or represents that its use would not infringe any privately owned ri

specific commercial product, process, or service by trade name, trademark, manufacturer, or othimply its endorsement, recommendation, or favoring by the Government or any agency thereof. authors and/or presenters expressed herein do not necessarily state or reflect those of MRI, the agency thereof. 
Why replace ITO?

• ITO is not ideal• CNT contact could 

interpenetrate into the active layer 

• Potentially hole 

selective contact

• Solution processable -

fully printed cell

• Work function similar to 

that of ITO
Resistance vs. Transmitt

SWCNT layers

The R

s/T performance of 

the SWCNT coating is continually improving
‘Conventional’ excitonic s

• Interpenetrated 

hole and electron conductors.

• Excitons dissociate 

at interface between P3HT and PCBM.

• Holes are 

transported in P3HT to PEDOT, where they transfer to ITO.
Energy diagram SWCNT bas
Device structures

SWCNT Denanotube disheated (65°CPEDOT:PScoating P3HT:PCBchlorobenzespin coatingAl vapor de
Devices made by drop c

• Active layer 

thickness of 500-1000 nm

• Strong 

rectification -SWCNT is hole specific contact

With PEDOT:PSS
Device without PED

• Lower 

efficiency, but still rectifying.

• Room for 

improvement

– Layer thickness– Solvent– Reduce contact 

resistance

– Increase shunt 

resistance
EQE of device without P

• Large amount of 

recombination in the bulk of the device.

• Needs 

optimization of layer thickness -spin casting!

P3HT
SEM cross section of sp

devices of 100 nm-thick ac

Incomplete 

Some tubes “stick” out
1.4 % Device without PED

• Dev

slig

• 1.4% 

3 timthe dev

• Fur

optipos
External Quantum efficie

1.4% device

PCBM

P3HT
SWCNT-based Device with PE

• Di-chlorobenzene

solvent

• Efficiencies of 2.6%• Very good 

rectification

• Less recombination 

than device without PEDOT

• Contact of 

nanotubes with PCBM in the active layer is detrimental?
Conclusions

• Organic solar cells with efficiencie

1.43% conversion efficiency that and no PEDOT:PSS, are demons

• A cell without ITO, but with PEDO

2.6% conversion efficiency

• Due to porous nature of SWCNT 

optimization of the active layer is 

• SWCNT electrodes bring one ste

goal of a fully printable, organic s