8/3/2019 Influence of Trap-Assisted Recombination on PolymerFullerene Solar Cells , Carsten Deibel et al, SPIE 2011 in San Diego
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Influence of
Trap-Assisted Recombination on
PolymerFullerene Solar Cells
C. Deibel, J. Lorrmann, A. Baumann, J. Gorenflot,
A. Wagenpfahl, J. Rauh,* V. Dyakonov
Julius-Maximilians-University of Wrzburg, Germany
* formerly known as Julia Schafferhans :-)SPIE Optics+Photonics
25th August 2011 in San Diego
8/3/2019 Influence of Trap-Assisted Recombination on PolymerFullerene Solar Cells , Carsten Deibel et al, SPIE 2011 in San Diego
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PP diss
internal
bulk rec
P rec
Recombination Mechanisms: Overview
2
glass
PEDOT
V
Photo-!current
external
Surface!loss
P
extract
P surface!rec
PP diss
internal
bulk rec
P rec
extraction at wrong
electrode due to diffusion(PRL 105, 266602 (2010))
surface recombination(PRB 82, 115306 (2010))
geminate recombination(PRL 103, 036402 (2009))
nongeminate recombination
P = Polaron; PP = Polaron Pair
8/3/2019 Influence of Trap-Assisted Recombination on PolymerFullerene Solar Cells , Carsten Deibel et al, SPIE 2011 in San Diego
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DOS
LUMO
Etransport
HOMO
ECT
Energy
a) b) d)c)
Etransport
Etailstate traps
Etailstate traps
Edeep traps
e)
Nongeminate Recombination
3, Free with Free (e)
Disordered System: all charges localised, hopping
concentration: free
8/3/2019 Influence of Trap-Assisted Recombination on PolymerFullerene Solar Cells , Carsten Deibel et al, SPIE 2011 in San Diego
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Recombination Order
4
Geminate Recombination:
concentration independent lifetime
Nongeminate Recombination: bimolecularconcentration dependent (effective) lifetime
2nd order
typical for photogeneration w/out traps
1st order
asymmetric doping or deep traps
1st order
8/3/2019 Influence of Trap-Assisted Recombination on PolymerFullerene Solar Cells , Carsten Deibel et al, SPIE 2011 in San Diego
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Langevin recombination
Nongeminate Recombination
5
glass
PEDOT
V(1)
(2)
(1)
2nd order recombination?
Langevin? reduced?
influence of traps?
RLangevin = np
=q
(e + h)
8/3/2019 Influence of Trap-Assisted Recombination on PolymerFullerene Solar Cells , Carsten Deibel et al, SPIE 2011 in San Diego
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Photo-CELIV
Experimental Method
6
ns laser pulse
delay time /recombination at V=Voff
charge extraction
1.2
1.0
0.8
0.6
0.4
0.2
j[x10
-3A
/cm
2]
0.80.40.0
t [x10-3
s]
Photo-CELIVdelay dependent @ T=150 KP3HT:PCBM 1:0.8
delay time tdelay betweenlaser and voltage pulse
shortdelay
longdelay
mobility and
carrier concentration
simultaneously
and transient absorption for comparison
8/3/2019 Influence of Trap-Assisted Recombination on PolymerFullerene Solar Cells , Carsten Deibel et al, SPIE 2011 in San Diego
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P3HT:PCBM (annealed) measured by photo-CELIV
Bulk Recombination
7
1020
1021
1022
n[m
-3]
10-7
10-6
10-5
10-4
10-3
10-2
tdelay [s]
125 K
300 K
P3HT:PCBM 1:0.8annealed
Andreas Baumann
temperature dependence
same as for mobility
typical for Langevin
recombination
RLangevin = np
= q(e + h)
8/3/2019 Influence of Trap-Assisted Recombination on PolymerFullerene Solar Cells , Carsten Deibel et al, SPIE 2011 in San Diego
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Analysis: Fitting to the Continuity Equation
1021
2
3
456
1022
2
3
45
next[m
-3]
10-7
10-6
10-5
10-4
10-3
10-2
tdelay [s]
experiment
T=150K
P3HT:PCBM 1:0.8
8
P3HT:PCBM (annealed) measured by photo-CELIV
8/3/2019 Influence of Trap-Assisted Recombination on PolymerFullerene Solar Cells , Carsten Deibel et al, SPIE 2011 in San Diego
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Analysis: Fitting to the Continuity Equation
dn
dt=
n
1021
2
3
456
1022
2
3
45
next[m
-3]
10-7
10-6
10-5
10-4
10-3
10-2
tdelay [s]
experiment
MR: = 6.610-4
s
T=150K
P3HT:PCBM 1:0.8
Monomolecular Recombination?
8/3/2019 Influence of Trap-Assisted Recombination on PolymerFullerene Solar Cells , Carsten Deibel et al, SPIE 2011 in San Diego
10/25
Langevin Recombination?
Analysis: Fitting to the Continuity Equation
1021
2
3
456
1022
2
3
45
next[m
-3]
10-7
10-6
10-5
10-4
10-3
10-2
tdelay [s]
experiment
MR: = 6.610-4
s
Langevin
T=150K
P3HT:PCBM 1:0.8
10
dn
dt=
q
r0
| {z }
n2
L
8/3/2019 Influence of Trap-Assisted Recombination on PolymerFullerene Solar Cells , Carsten Deibel et al, SPIE 2011 in San Diego
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Reduced Langevin Recombination!
Analysis: Fitting to the Continuity Equation
1021
2
3
456
1022
2
3
45
next[m
-3]
10-7
10-6
10-5
10-4
10-3
10-2
tdelay [s]
experiment
MR: = 6.610-4
s
Langevin
red. Langevin: = 0.057
T=150K
P3HT:PCBM 1:0.8
11
dn
dt=
q
r0
| {z }
n2
L
8/3/2019 Influence of Trap-Assisted Recombination on PolymerFullerene Solar Cells , Carsten Deibel et al, SPIE 2011 in San Diego
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Analysis: Fitting to the Continuity Equation
1021
2
3
456
1022
2
3
45
next[m
-3]
10-7
10-6
10-5
10-4
10-3
10-2
tdelay [s]
experiment
MR: = 6.610-4
s
Langevin
red. Langevin: = 0.057
k+1n+1
with +1=2.41
T=150K
P3HT:PCBM 1:0.8
12
Recombination Order > 2 ? dn
dt= k+1 n
+1
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Recombination Order
13
3.4
3.2
3.0
2.8
2.6
2.4
2.2
2.0
recombinationorder
300250200150
T [K]
P3HT:PCBM 1:0.8
pristineannealed
BR
P3HT:PCBM measured by photo-CELIV
Andreas Baumann
2nd order or higher
bimolecular
recombination
the more disordered
pristine sample: higher rec. order
+1
8/3/2019 Influence of Trap-Assisted Recombination on PolymerFullerene Solar Cells , Carsten Deibel et al, SPIE 2011 in San Diego
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7
6
5
4
3
2
1
OrderofDecay
30025020015010050
Temperature [K]
P3HT:PCBM
For Comparison: Transient Absorption
14
P3HT:PCBM (annealed) measured by transient absorption
P3HT:PCBM,similar results as
compared to
photo-CELIV
Julien Gorenflot
7
6
5
4
3
2
1
OrderofDecay
30025020015010050
Temperature [K]
P3HT
P3HT:PCBM
P3HT >140K due
to polarons;
second order
recombination!
neat P3HT: no
phase separation
+1
8/3/2019 Influence of Trap-Assisted Recombination on PolymerFullerene Solar Cells , Carsten Deibel et al, SPIE 2011 in San Diego
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2
4
68
10
2
4
68
100
2
4
68
1000
65432
2 /
2.0 nm
2.8 nm
pBTCT-C12:PC61BM1:01:11:4
Similar for Intercalating Materials!
15
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
recombinationorder
300280260240220200180
T / K
pBTCT-C12:PC61BMphoto-CELIV 1:1
1:4TRMC 1:1
1:4
Adv. Funct. Mater. 21, 1687 (2011)
8/3/2019 Influence of Trap-Assisted Recombination on PolymerFullerene Solar Cells , Carsten Deibel et al, SPIE 2011 in San Diego
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carrier concentration dependent mobility
Shuttle et al, Adv. Funct. Mater 20, 698 (2010)
Causes for High Recombination Order?
16
influence of trappingZaban et al, Chem. Phys. Chem. 4, 859 (2003)
Nelson, PRB 67, 155209 (2003)
influence of phase separation idea, but without change of order: Koster et al, APL 88, 052104 (2006)
qualitatively: Baumann et al, Adv. Funct. Mater. 21, 1687 (2011)
8/3/2019 Influence of Trap-Assisted Recombination on PolymerFullerene Solar Cells , Carsten Deibel et al, SPIE 2011 in San Diego
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17
Concentration Dependent Mobility?
56
10-10
2
3
4
56
10-9
2
3
4
[m
2/Vs
]
1020
1021
1022
n [m-3
]
125 K150 K175 K200 K300 K
P3HT:PCBM 1:0.8annealed
at least, not for annealed
P3HT:PCBM solar cells
P3HT:PCBM (annealed) measured by photo-CELIV
Andreas Baumann
C f f
8/3/2019 Influence of Trap-Assisted Recombination on PolymerFullerene Solar Cells , Carsten Deibel et al, SPIE 2011 in San Diego
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Concentration Dependence of Rec. Prefactor
18
P3HT:PCBM (annealed) measured by photo-CELIV
fit:
if it were pure Langevin:
nand (n) from CELIV
and k from fitting CELIV
Andreas Baumann
10-20
10-19
10-18
10-17
kBR
[m3 /s
]
1020
1021
1022
n [m-3
]
P3HT:PCBM 1:0.8annealed
fit
125 K175 K300 K
10-20
10-19
10-18
10-17
kBR
[m3 /s
]
1020
1021
1022
n [m-3
]
P3HT:PCBM 1:0.8annealed
fit Langevin
125 K175 K300 K
C i D d f R P f
8/3/2019 Influence of Trap-Assisted Recombination on PolymerFullerene Solar Cells , Carsten Deibel et al, SPIE 2011 in San Diego
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consequence:
is not universal
Concentration Dependence of Rec. Prefactor
19
P3HT:PCBM (annealed) measured by photo-CELIV
Andreas Baumann
10-20
10-19
10-18
10-17
kBR
[m3 /s
]
1020
1021
1022
n [m-3
]
P3HT:PCBM 1:0.8annealed
fit Langevin
125 K175 K300 K
High recombinationorder in part due tonot all carriers being
able to recombine withone another (no nt2)
T i ?
8/3/2019 Influence of Trap-Assisted Recombination on PolymerFullerene Solar Cells , Carsten Deibel et al, SPIE 2011 in San Diego
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Trapping?
20
trapping in extrinsic trapsdoes occur
generally: in a hopping
system, trapping also withinintrinsic density of states
APL 93, 093303 (2008), Org. Electron. 11, 1693 (2010),
Adv. Ener. Mater. 1, 655 (2011)
P3HT:PCBM (annealed) by Thermally Stimulated Currents
6x1021
5
4
3
2
1
0trapdensity(lowerlimit)[m
-3]
400300200100
activation energy [meV]
P3HT:PC61BM
PC61BM
P3HT
T3
T2
T1
Julia Rauh
Trap density (Lower Limit)
P3HT:PCBM: 6-81022 m-3
P3HT: 11022 m-3
Ph S ti ?
8/3/2019 Influence of Trap-Assisted Recombination on PolymerFullerene Solar Cells , Carsten Deibel et al, SPIE 2011 in San Diego
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Phase Separation?
21
Scenario
Polymer
Fulle
rene
!
Modelling
solving the continuity equation trapping and release
exponential DOS (intrinsic)=> recombination order >2
here: Rnfreepfree
due to phase separation
et
delayed recombination
due to emission from trap
Jens Lorrmann
R bi ti O d 1
8/3/2019 Influence of Trap-Assisted Recombination on PolymerFullerene Solar Cells , Carsten Deibel et al, SPIE 2011 in San Diego
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Recombination Order +1
22Jens Lorrmann
even without phase separation
... but stronger with it!
>10.0
I t C t V lt Ch t i ti
8/3/2019 Influence of Trap-Assisted Recombination on PolymerFullerene Solar Cells , Carsten Deibel et al, SPIE 2011 in San Diego
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freefree recombination
150
100
50
0
-50
-100
Currentdens
ity[A/m
]
0.80.40.0-0.4
Voltage [V]
disorder
disorder
illum. dark25 meV50 meV75 meV
100 meV125 meV
150
100
50
0
-50
-100
Currentdens
ity[A/m
2]
0.80.40.0-0.4
Voltage [V]
disorder
illum. dark25 meV50 meV75 meV100 meV125 meV
Impact on CurrentVoltage Characteristics
23
freefree and freetrappedrecombination
Alexander Wagenpfahl
unfortunately, probably a mixture of both in real devices:
pure and intermixed phases
C l i N i t R bi ti
8/3/2019 Influence of Trap-Assisted Recombination on PolymerFullerene Solar Cells , Carsten Deibel et al, SPIE 2011 in San Diego
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carrier concentration dependent mobility
- CELIV: order > 2 also for cases with (n) = const
- part of concentration dependence from R f(nt2)
influence of trapping
- significant trap concentration, nt >> nc
=> multiple-trapping-and-release
influence of phase separation
- 2nd order recombination in neat polymer indicates:
phase separation plays role in blends high order
order > 2 from delayed bimolecular recombination
due to trapping
Conclusions: Nongeminate Recombination
24
A k l d t
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Thank You!
Acknowledgments
25
EP VI
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