Supplementary Information
Efficiency Enhancement for Bulk Heterojunction Photovoltaic Cells
via Incorporation of Alcohol Soluble Conjugated Polymer Interlayer
Yu Chen,1,3* Zhitao Jiang,2,3* Mei Gao,3 Scott E. Watkins,3 Ping Lu,2, † Haiqiao Wang,1,‡
Xiwen Chen3,§
1
State Key Laboratory of Organic-Inorganic Composites, Key Laboratory of Carbon Fiber
and Functional Polymers, Ministry of Education, Beijing University of Chemical Technology,
Beijing, 100029, P. R. China.
2
Chemistry Department, Zhejiang University, Hangzhou, 310027, P. R. China
3
CSIRO Materials Science and Engineering, Clayton, VIC 3168, Australia.
Materials
[6,6]-phenyl-C61-butyric acid methyl ester (PC61BM, purity > 99.0%) was bought from
NANO-C
(U.S
Patent
No.
5,739,376),
and
used
as
received.
Poly(3,4-
ethylenedioxythiophene)-Polystyrenic surfonic acid (PEDOT:PSS, Clevious P VP AI 4083)
was purchased from H. C. Starck. Other chemicals were purchased from Acros Chemical Co.
and Merck Pty limited. Poly (9,9-bis(6'-((N,N,N-trimethyl) ammonium) hexyl)-2,7-fluorene)
dibromide
(PFNBr)
and
poly[2,7,2',7'-spirobifluorene-co-(9,9-bis(6'-((N,N,N-trimethyl)
ammonium) hexyl)-2,7-fluorene) dibromide] (PSFNBr) are made according to a literature
method.S1 poly[(9,9-bis(3'-((N,N,-dimethyl) amino) propyl)-2,7-fluorene)] (PFN) and
*
These authors contribute equally.
†
Pinglu@zju.edu.cn
‡
Wanghaiqiao@mail.buct.edu.cn
Xiwen.Chen@csiro.au
§
1
poly[2,7,2',7'-spirobifluorene-co-(9,9-bis(3'-((N,N,-dimethyl) amino) propyl)-2,7-fluorene)]
(PSFN) are made by Yamamoto polymerization according to previous report.S2 The feed
content of the spiro-fluorene monomer is 5%.
Instrumentations and Measurements
Ionization potential of the surface of the films was measured by Photo electron
spectroscopy in Air (PESA) on a Riken Keiki AC2 PESA spectrometer with a power setting
of 5 nW and a power number of 0.5. UV-Vis spectra were measured with Cary 5E UV-VisNIR spectrophotometer and photoluminescent spectra were recorded with Perkin Elmer
Luminescence Spectrometer LS 50. The samples were spin cast on PEDOT-PSS on glass.
The Atom Force Microscopy (AFM) measurement of the surface morphology was conducted
on the Asylum Research MFP-3D AFM in AC mode with a NSC15/AIBS Si cantilever
(resonant frequency around 325 kHz from µ-masch). The contact angle of the films was
measured with CAM 200 (KSV Instrument LID.) and the photos were taken with BASLER
A602f-2 camera. J-V characteristics of all devices were measured using a Keithley 2410
Source Meter Unit. Solar cell performance was measured under an Air Mass 1.5 Global (AM
1.5 G) Oriel solar simulator fitted with a 1000 W Xe lamp filtered to give an output of 100
mW/cm2 in a glove-box.
The Incident Photon Collection Efficiency (IPCE) data was
collected using an Oriel 150W Xe lamp coupled to a monochromator and an optical fibre.
The IPCE was calibrated with a standard, unfiltered Si cell. For IPCE measurement, the
devices were encapsulated and measured in air.
Device fabrication:
The solar cells were prepared on commercial glass slides coated with patterned indium tin
oxide (25mm × 25mm patterned ITO glass, sheet resistance of 15 Ω/sq from Kintech, HK)
which were cleaned with ultrasonic bath in turns of using detergent solution, deionized water,
acetone and isopropanol. Then, an ~80 nm thick active layer was spin-coated on top of a ~40
2
nm thick PEDOT:PSS (Clevious P VP AI 4083 from H.C.Starck) layer on the cleaned
patterned ITO glass substrate from a chlorobenzene solution of PFOTBT:PC61BM with a
weight ratio of 1 : 3. The cathode interfacial layers were subsequently deposited atop the
active layer by spin-coating from 0.15 mg/mL PFNBr at 5000 rpm/sec, 0.25 mg/mL for
PSFNBr at 7000 rpm/sec, and 0.20 mg/mL for both PFN and PSFN solutions at 7000 rpm/sec
in methanol respectively, and all of the cathode interfacial layers were too thin to be
measured by the DEKTAK 6M Stylus Profiler. However, we have also tested other different
thickness of PFNBr interfacial layer for devices (e.g. the speed for spin-coating of interfacial
layers was in terms of 3000 rpm/sec, 5000 rpm/sec and 7000 rpm/sec), none of the others was
as good as the one we adopted in this work. Finally, 100 nm of Al was thermally deposited in
a vacuum of 1.5 x 10-7 Torr to form the top electrode. The working area of each cell was 0.10
cm2. For comparison, some of the devices were evaporated with a 20 nm of calcium and
some were spin cast with methanol solvent only at 7000 rpm before evaporation of
aluminium. For the devices with P3HT-PC61BM as active layer, the fabrication process is
similar except that the weight ratio of P3HT to PC61BM is 1:0.8, and the thickness of this
layer is around 110 nm, spin cast from chlorobenzene solution. This layer was annealed at
150 oC for 10 minutes before spin casting of the interfacial layers.
3
Supplementary Results
FIG.S1. IPCE spectra of devices with CPE layer on PFOTBT-PC61BM active blend.
4
FIG.S2. The molecular structures of the neutral interfacial materials (up) and J-V
characteristics of PFOTBT:PC61BM devices with deposition of PFN (blue) and PSFN (green)
under AM 1.5G irradiation (100 mW/cm2) (down).
5
Fig. S3. PESA spectra of PFOTBT-PCBM layers on PEDOT-PSS without (up) and with
(down) spin casting of methanol on top.
6
0.6
16
Pristine film
pristine
methanol cast
0.4
PL intensity
Absorbance
0.5
0.3
0.2
methanol cast
12
8
4
0.1
0
0
300
400
500
600
700
800
600
Wavelength (nm)
700
800
900
Wavelength (nm)
Fig. S4. UV and PL spectra (excited at 540 nm) of PFOTBT-PC61BM films with and without
spin casting methanol on top.
Fig. S5. Water contact angles of PFOTBT-PC61BM films with PFN (43.4°) and PSFN (58.5°)
on top, respectively.
Table SI: OPV performance based on devices ITO/PEDOT-PSS/P3HT:PC61BM (1:0.8 wt in
chlorobenzene)/ blank or modification /Al. No post-annealing except the one marked.
Interfacial layer
Blank
With post annealed
With Ca/Al
cathode
With PFNBr
With PFN
With PSFNBr
With PSFN
With methanol
treatment
Voc (V)
0.44
0.62
0.60
Jsc (mA/cm2)
9.15
9.68
8.52
FF (%)
54.38
60.46
67.68
PCE (%)
2.19
3.63
3.46
0.50
0.52
0.56
0.60
0.52
9.56
8.94
8.70
9.65
9.38
57.64
58.12
63.36
66.16
59.65
2.76
2.70
3.09
3.83
2.91
7
Fig.S6. J-V characteristics of devices ITO/PEDOT/P3HT:PC61BM(1:0.8 wt in CB)/ blank or
modification /Al under AM 1.5G irradiation (100 mW/cm2). No post-annealing except the
one marked.
Reference:
S1
R. Q. Yang, H. B. Wu, Y. Cao and G. C. Bazan, J. Am. Chem. Soc. 128, 14422 (2006).
X. Chen, J. L. Liao, Y. Liang, M. O. Ahmed, H. E. Tseng, S. A. Chen, J. Am. Chem. Soc.
125, 636 (2003).
S2
8