Efficient Organic Solar Cells based on Small …...Efficient Organic Solar Cells based on Small Molecules C. Körner, R. Fitzner, C. Elschner, F. Holzmüller, P. Bäuerle, K. Leo and

Fakultät Mathematik und Naturwissenschaften – Institut für Angewandte Photophysik http://www.iapp.de

Efficient Organic Solar Cells

based on

Small Molecules

C. Körner, R. Fitzner, C. Elschner, F. Holzmüller, P. Bäuerle, K.

Leo and M. Riede

DPG AKE Meeting 2013

AKE 7.2

05.03.2013

Organic Solar Cells

glass + ITO

hole transport layer

(HTL)

donor

acceptor

electron transport layer

(ETL)

metal

glass + ITO


(HTL)

donor

acceptor

Slide 2 DPG AKE Dresden 2013, AKE 7.2

donor

acceptor

donor:acceptor


(ETL)

metal

• charge transport

• easy to process

• limited to thin layers

(little absorption,

low currents)

flat heterojunction

(FHJ) • high currents

(small D/A distances)

• thicker layers possible

• charge transport disturbed

• higher recombination

• multi-parameter optimization

bulk heterojunction

(BHJ)

Christian Körner

Reasons/Ways for Improvement

towards Higher Efficiency


contacts

materials?

processing

issues? !!MOLECULES!!

module

integration?

material

purity?

stack

design?

Christian Körner


-1.5 -1.0 -0.5 0.0 0.5 1.0

-10

0

10

20

FHJ

cu

rre

nt

de

nsity (

mA

/cm

2)

bias (V)

Processing: Substrate Heating

increase FF in BHJ solar cells

(nano-)crystallinity

phase separation charge transport

-1.5 -1.0 -0.5 0.0 0.5 1.0

-10

0

10

20

FHJ

BHJ

cu

rre

nt

de

nsity (

mA

/cm

2)

bias (V)

-1.5 -1.0 -0.5 0.0 0.5 1.0

-10

0

10

20

FHJ

BHJ

BHJ heated

Tsub

= 88°C

cu

rre

nt

de

nsity (

mA

/cm

2)

bias (V)

substrate

heating

Tsub

= RT

Influence morphology

Christian Körner

The

Material System Slide 5 DPG AKE Dresden 2013, AKE 7.2

2006

K. Schulze

C. Uhrich

R. Schüppel

D. Wynands

M. Levichkova

H. Ziehlke

C. Körner

C. Elschner

2013

Molecules: Variability!

Christian Körner

The DCVnT-Zoo

3T 4T 5T 6T

Et

Me

Bu

** http://www.gimp-werkstatt.de/colorieren.php


Christian Körner

The DCVnT-Zoo


33

15

24

Christian Körner

Similar properties – different performance

The Starting Point


• outstanding performance for

compound 33

• high efficiency of 6.1%

reached already for non-

optimized standard device

Fitzner, Elschner et al., J. Am. Chem. Soc. 2012, 134, 11064

15

24

33

Tsub = 90°C

33

15

24

Christian Körner

Thin Film Morphology via GIXRD


pristine films:

highest crystallinity for comp. 15

mixed films:

highest crystallinity for comp. 33 33

15

24

15

24

33

15

24

33

15:C60

24:C60

33:C60

C60

pristine films mixed films

Fitzner, Elschner et al., J. Am. Chem. Soc. 2012, 134, 11064

Christian Körner

ongoing investigations!

d

Roadmap for High Efficiency


d

• optimize mixing ratio DCV5T/C60: 2:1

• optimal substrate temperature: Tsub=80°C

• optimize thickness of the active blend layer: 35-40nm

• optimize thickness of window layer: 35-40nm

Christian Körner

7.2% reached!


certified efficiency at Fraunhofer ISE: h = 7.2%

Christian Körner

0.0 0.2 0.4 0.6 0.8 1.0

-12

-10

-8

-6

-4

-2

0

2

300 400 500 600 700 800

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

curr

ent

density j (

mA

/cm

2)

voltage V (V)

hE

QE (

norm

.)wavelength (nm)

hE

QE

Summary


• molecules and thin film morphology are crucial for high efficiency

• record efficiency of 7.2% achieved for small molecule organic solar

cells

• Further optimization by

• increased absorption

• red-shifted absorption (optical gap at 1.4eV)

• tandem structures

• …

300 400 500 600 700 800 900

0.0

0.5

1.0

1.5

extinction c

oeffic

ient

k

wavelength (nm)

Christian Körner

Acknowlegdments


Thank You For Your

Attention

OSOL-group at IAPP

Christian Körner

Christian Körner Slide 14 IAPP Seminar Dissertation Talk - 2012/06/28

Thanks to the OSOL group

Appendix

Introduction


pictures taken from

• building integration

• facades

• mobile applications

• … http://www.fotoskizzen.de/deutschland/ fotografie/frankfurt-glasfassade.jpg

• leight-weight

• flexible

• cheap

• colorful

• transparent

• superior temperature, angle

and low-light performance

Christian Körner

Solar Cell Efficiency Development

Sources: NREL (www.nrel.gov/ncpv/images/efficiency_chart.jpg); heliatek press releases

Slide 17

12.0%

DPG AKE Dresden 2013, AKE 7.2 Christian Körner

HOMO

LUMO

Slide 18

1 2

4

4 5

5

3

photon absorption

(exciton generation)

exciton diffusion

charge transfer

charge transport

charge collection

ele

ctro

de

donor

accepto

r

ele

ctro

de

HOMO

LUMO

Charge Carrier Generation Scheme

C. Tang, APL 48, 183 (1986)

DPG AKE Dresden 2013, AKE 7.2

Christian Körner

glass + ITO

Organic Solar Cells

donor

acceptor


metal

Christian Körner

Organic Solar Cells


glass + ITO


(HTL)

donor

acceptor


(ETL)

metal

glass + ITO


(HTL)

donor

acceptor


(ETL)

metal Why transport layers?

• avoid charge transport to

wrong electrode

• set active layer to maximum of

optical field (window layers)

• independent of contact material

Christian Körner

Solar Cell Characterization

in

out

P

PPCE

1FF

jV-characteristics

VjPel

in

ocsc

P

FFVjPCE

in

MPPMPP

in

out

P

Vj

P

PPCE

ocV

scjMPP


Christian Körner

Substrate Heating

Review

DCV6T-Bu(1,2,5,6)

Substrate heating

David Wynands:

DCV4T

Christian Körner/Franz Selzer:

Substrate heating


Christian Körner

-1.0 -0.5 0.0 0.5 1.0

-10

0

10

20

30

j [m

A/c

m²]

U [V]

RT

80°C

110°C

33

Comparison 33 vs 15

• improvement up to Tsub=80°C

• above a critical temperature,

jsc and Voc are decreased


-1.0 -0.5 0.0 0.5 1.0

-10

0

10

20

30

j [m

A/c

m²]

U [V]

RT

80°C

110°C

140°C

15

• critical temperature higher

for compound 15

Variation of Substrate Temperature

Christian Körner

Morphological Changes upon

Substrate Heating


300 400 500 600 700 8000.0

0.2

0.4

0.6

0.8

Tsub

= 140°C

Tsub

= 80°C/110°C

E

QE

wavelength [nm]

Tsub

= RT

DCV5T

absorption

C60

absorption

15

Koerner et al., …DCV4T…, Organic Electronics 13, … … (2012)

Christian Körner

Substrate Heating

Detailed Investigations

absorption decrease:

surface topography (AFM):

increased roughness

phase demixing

PL quenching decrease:

30°C

90°C

structure investigations (GIXRD): together with Chris Elschner, in coop. with Univ. of Stanford

excitons are lost

decrease in jsc p-stacking / molecular orientation changed

DCV4T:C60

2:1, 20nm

C60 (15nm)

glass


Christian Körner

Christian Körner Slide 26 IAPP Seminar Dissertation Talk - 2012/06/28

Organic Solar Cells

ele

ctro

de

absorb

er

ele

ctro

de

electrode

donor

acceptor

electrode

absorber


Christian Körner

Organic Solar Cells

ele

ctro

de

absorb

er

ele

ctro

de

HOMO

LUMO

very strong exciton binding energy

negligible photocurrent!

E


Christian Körner

molecules: narrow-band absorbers

Organic Solar Cells

electrode

donor

acceptor

electrode

ele

ctro

de

accepto

r

donor

ele

ctro

de

photoactive

material

wavelength

absorp

tion

solar radiation intensity

broad-band absorber x


Christian Körner

Substrate Heating

Review

DCV6T-Bu(1,2,5,6)

Similar results for DCV6T-Et(2,2,5,5)

Substrate heating

David Wynands:

Slide 30 Christian Körner et. al. DPG AKE Dresden 2013

Substrate Heating

Solar Cell Characteristics

glass + ITO

C60 (15nm)

DCV4T:C60

2:1, 20nm

ETL

(55nm)

Au (50nm)

DCV4T x

x

x

x x

x x

x

x

x

x

x

x

x x

x


Substrate Heating

Blend Layer Absorption

DCV4T:C60

2:1, 20nm

C60 (15nm)

glass

TRA 1

C60

DCV4T

directed

transmission

integrated

transmission

decrease in absorption jsc


Substrate Heating

Blend Layer Topography (AFM)

DCV4T:C60

2:1, 20nm

C60 (15nm)

glass

30°C 50°C 70°C 90°C

AFM-pictures taken by Franz Selzer

30°C

90°C


Substrate Heating

Photoluminescence Quenching

DCV4T:C60

2:1, 20nm

C60 (15nm)

glass

S0

S1

CTD/A

donor

reference: blends:

x


DCV4T

(13.3nm)

glass

C60 (15nm)

C60 (6.7nm)

@ 9

0°C

Substrate Heating

Photoluminescence Quenching

DCV4T:C60

2:1, 20nm

C60 (15nm)

glass

reference: blends:


Substrate Heating

Structure Investigations (GIXRD)

• increased crystallinity of DCV4T and C60

phase : 30°C (blue) 90°C (orange)

• Change in p-stacking direction (out-of-plane

in-plane reflections)

= explanation for decrease in absorption

(unfavorable molecule orientation to

incoming light)


Documents

Efficient Organic Solar Cells based on Small …...Efficient Organic Solar Cells based on Small Molecules C. Körner, R. Fitzner, C. Elschner, F. Holzmüller, P. Bäuerle, K. Leo and