efficient organic solar cells based on small …...efficient organic solar cells based on small...
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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
hole transport layer
(HTL)
donor
acceptor
Slide 2 DPG AKE Dresden 2013, AKE 7.2
donor
acceptor
donor:acceptor
electron transport layer
(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
Slide 3 DPG AKE Dresden 2013, AKE 7.2
contacts
materials?
processing
issues? !!MOLECULES!!
module
integration?
material
purity?
stack
design?
Christian Körner
Slide 4 DPG AKE Dresden 2013, AKE 7.2
-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
Slide 6 DPG AKE Dresden 2013, AKE 7.2
Christian Körner
The DCVnT-Zoo
Slide 7 DPG AKE Dresden 2013, AKE 7.2
33
15
24
Christian Körner
Similar properties – different performance
The Starting Point
Slide 8 DPG AKE Dresden 2013, AKE 7.2
• 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
Slide 9 DPG AKE Dresden 2013, AKE 7.2
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
Slide 10 DPG AKE Dresden 2013, AKE 7.2
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!
Slide 11 DPG AKE Dresden 2013, AKE 7.2
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
Slide 12 DPG AKE Dresden 2013, AKE 7.2
• 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
Slide 13 DPG AKE Dresden 2013, AKE 7.2
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
Slide 16 DPG AKE Dresden 2013, AKE 7.2
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
Slide 19 DPG AKE Dresden 2013, AKE 7.2
metal
Christian Körner
Organic Solar Cells
Slide 20 DPG AKE Dresden 2013, AKE 7.2
glass + ITO
hole transport layer
(HTL)
donor
acceptor
electron transport layer
(ETL)
metal
glass + ITO
hole transport layer
(HTL)
donor
acceptor
electron transport layer
(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
Slide 21 DPG AKE Dresden 2013, AKE 7.2
Christian Körner
Substrate Heating
Review
DCV6T-Bu(1,2,5,6)
Substrate heating
David Wynands:
DCV4T
Christian Körner/Franz Selzer:
Substrate heating
Slide 22 DPG AKE Dresden 2013, AKE 7.2
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
Slide 23 DPG AKE Dresden 2013, AKE 7.2
-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
Slide 24 DPG AKE Dresden 2013, AKE 7.2
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
Slide 25 DPG AKE Dresden 2013, AKE 7.2
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
Slide 27 DPG AKE Dresden 2013, AKE 7.2
Christian Körner
Organic Solar Cells
ele
ctro
de
absorb
er
ele
ctro
de
HOMO
LUMO
very strong exciton binding energy
negligible photocurrent!
E
Slide 28 DPG AKE Dresden 2013, AKE 7.2
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
Slide 29 DPG AKE Dresden 2013, AKE 7.2
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
Slide 31 Christian Körner et. al. DPG AKE Dresden 2013
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
Slide 32 Christian Körner et. al. DPG AKE Dresden 2013
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
Slide 33 Christian Körner et. al. DPG AKE Dresden 2013
Substrate Heating
Photoluminescence Quenching
DCV4T:C60
2:1, 20nm
C60 (15nm)
glass
S0
S1
CTD/A
donor
reference: blends:
x
Slide 34 Christian Körner et. al. DPG AKE Dresden 2013
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:
Slide 35 Christian Körner et. al. DPG AKE Dresden 2013
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)
Slide 36 Christian Körner et. al. DPG AKE Dresden 2013