Do the Defects Make it Work? Defect Engi

Conjugated Polymer Films and Their S

Brian A. Gregg*, Dong Wang, Matthew O. Reese and 

National Renewable Energy Laboratory

NREL/PR-270-43277Presented at the 33rd IEEE Photovoltaic Specialist Conference held May 11-16, 2
Free carrier density at zero field, 

p

Intrinsic SC, 

Ebg = 2.0 eV

pf0 = 

nf0

Molecular SCs (e.g., porphyrins, 1011 - 1

perylenes, phthalocyanines)

Peumans, P.; Yakimov, A.; Forrest, S. R., J. Appl. Phys. 2003, 93, (

Gregg, B. A.; Chen, S.-G.; Cormier, R. A., Chem. Mater. 2004, 16, 

π-conjugated polymers (e.g., cm-3

P3HT, MDMO-PPV)

Jarrett, C. P.; Friend, R. H.; Brown, A. R.; de Leeuw, D. M., J. App

6289. Chen, S.-G.; Stradins, P.; Gregg, B. A., J. Phys. Chem. B 200

C.; Geens, W.; Mehra, A.; Kumar, V.; Aernouts, T.; Poortmans, J.; Mertens, R.; 

Phys. 2001, 89, 3804. Dicker, G.; de Haas, M. P.; Warman, J. M.; de Leeuw, D

J. Phys. Chem. B 2004, 108, 17818; Mozer, A. J.; Sariciftci, N. S.; Piv

Juska, G.; Brassat, L.; Bässler, H., Phys. Rev. B 2005, 71, 035214.
-0.25

-0.2

-0.15

-0.1

-0.05

0

0.05

0.1

-400 -200 0 200 

E, eV

x, Å

F = 2 V/μm

groundstate

F = 0

E

a

0

E

d

Poole-Frenkel currents

J = q μ0 F nd exp((-Ea0 +(q3/πε0ε)1/2 F1

Binding energy between charges > kBT because 

constant and localized carrier wavefunctions. 

excitons, doping, charge separation and 

nf0 ≈ 
The field-dependence of 

μ may be similar to th

included in the original PF model—> P

Band diagram with trapped charges 

induced conduction band fluctu

correlateddisorder
N N

N

N

N

N

N N

Ti=O

Ecb

EvbEF

Non-Covalent Defects: Molecular sem

have only non-covalent defects (and chemic
Covalent Defects: π-conjugated polyme

covalent and non-covalent defects (and chem
Chemically treating covalent defects in P

nucleophiles and electrophiles

No reaction with pristine material
Dark current-field curves for treated and u

0

400800

12001600

0 2 10

4 4 10

4 6 10

4 8 10

J, mA/cm2

Field, V/cm

Me

2

S

un

P3HT
Exciton diffusion length before and after chem

0

0.10.20.30.40.50.60.70.8

0 4 8 12 16 20 24 28 

Flq/Fl

uq

d, nm

untreatedL

ex

 = 7 ± 1 n

Me

2

SO

4

L

ex

 = 13 ± 1 n

MeO

-

L

ex

 = 9 ± 2 n
Results of chemical treatmen

Table 1. 

Treatment 

Relative PL 

Quantum 

Yield

Zero-field 

conductivity, 

0, x 10-7 S/cm

EaJ0, meV PL Life -time 

avg, ps 

Lex

P3HT: none 1.00 14 233 401 

MeO- 1.35 3 276 579 

MeI 0.92 29 223 354 -

Me2SO4 0.54 46 210 285 1

MDMO-PPV: non 1.00 e 1.4 280 866 1

MeO- 1.22 0.51 306 1020 1
Bulk heterojunction OPV cells made fro

treated P3HT, and controls

-10

-5

05

10

0 0.2 0.4 0

J, mA/cm

2

V

control, air control treated treated, air

OPV cells under 1 sun
Impurities make it work: a peryene diimide/p

P. Peumans, et al, Adv. Mater. 2008, 20, 2
Summary

• Charged defects produce 1015 - 1017 cm-

• Treatment with nucleophiles decreases p

treatment with electrophiles does not ch

increases σ

• Both treatments increase μp, Lex and stab

photo-degradation

• Charged defects can improve OPV by in

conductivity and creating interfacial ele

• But they hurt μp, Lex and chemical stabil

• A better way: synthesize materials witho

defects and dope with purposely added,