influence of trap-assisted recombination on polymer–fullerene solar cells , carsten deibel et al, ...

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


2/25

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


3/25

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


4/25

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


5/25

Langevin recombination

Nongeminate Recombination

5

glass

PEDOT

V(1)

(2)

(1)

2nd order recombination?

Langevin? reduced?

influence of traps?

RLangevin = np

=q

(e + h)


6/25

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


7/25

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)


8/25

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



9/25


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?


10/25

Langevin Recombination?


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


11/25

Reduced Langevin Recombination!


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


12/25


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


13/25

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


14/25

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


15/25

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)


16/25

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)


17/25

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


at least, not for annealed

P3HT:PCBM solar cells


Andreas Baumann

C f f


18/25

Concentration Dependence of Rec. Prefactor

18


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

]


fit

125 K175 K300 K

10-20

10-19

10-18

10-17

kBR

[m3 /s

]

1020

1021

1022

n [m-3

]


fit Langevin

125 K175 K300 K

C i D d f R P f


19/25

consequence:

is not universal

Concentration Dependence of Rec. Prefactor

19


Andreas Baumann

10-20

10-19

10-18

10-17

kBR

[m3 /s

]

1020

1021

1022

n [m-3

]


fit Langevin

125 K175 K300 K

High recombinationorder in part due tonot all carriers being

able to recombine withone another (no nt2)

T i ?


20/25

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 ?


21/25

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


22/25

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


23/25

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


24/25

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


25/25

Thank You!

Acknowledgments

25

EP VI

[email protected]

www.disorderedmatter.eu
http://www.disorderedmatter.eu/http://www.disorderedmatter.eu/mailto:[email protected]:[email protected]

influence of trap-assisted recombination on polymer–fullerene solar cells , carsten deibel et al, ...

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