Alcohol/water-soluble porphyrins as cathode interlayers in high-performance polymer solar cells

Article abstract of DOI:10.1007/s11426-014-5218-4

Three alcohol/water-soluble porphyrins (Zn-TPyPMeI:zinc(II) meso-tetra(N-methyl-4-pyridyl) porphyrin tetra-iodide, Zn-TPyPAdBr:zinc(II) meso-tetra[1-(1-adamantylmethyl ketone)-4-pyridyl] porphyrin tetra-bromide and MnCl-TPyPAdBr:man-ganese(III) meso-tetra

Full text of DOI:10.1007/s11426-014-5218-4

SCIENCE CHINA
Chemistry
•
ARTICLES •
Feb dr uo ai :r y1 02 . 01 10 50 7/ sV1 1o 4l . 25 68 -0 1N4 o- 5. 22 :1 18 –- 48
doi: 10.1007/s11426-014-5218-4
Alcohol/water-soluble porphyrins as cathode interlayers in
high-performance polymer solar cells
Tao Jia, Weilong Zhou, Fenghong Li, Yajun Gao, Lu Wang, Jianxiong Han,
*
Jingying Zhang & Yue Wang
State Key Laboratory of Supramolecular Structure and Materials, Jilin University, Changchun 130012, China
Received June 28, 2014; accepted July 21, 2014
Three alcohol/water-soluble porphyrins (Zn-TPyPMeI:zinc(II) meso-tetra(N-methyl-4-pyridyl) porphyrin tetra-iodide, Zn-
TPyPAdBr:zinc(II) meso-tetra[1-(1-adamantylmethyl ketone)-4-pyridyl] porphyrin tetra-bromide and MnCl-TPyPAdBr:man-
ganese(III) meso-tetra[1-(1-adamantylmethyl ketone)-4-pyridyl] porphyrin tetra-bromide were employed as cathode interlayers
to fabricate polymer solar cells (PSCs). The PC71BM ([6,6]-phenyl C71 butyric acid methyl ester) and PCDTBT (poly[N-9″-
hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)])-blend films were used as active layers in
polymer solar cells (PSCs). The PSCs with alcohol/water-soluble porphyrins interlayer showed obviously higher power con-
version efficiency (PCE) than those without interlayers. The highest PCE, 6.86%, was achieved for the device with MnCl-
TPyPAdBr as an interlayer. Ultraviolet photoemission spectroscopic (UPS), carrier mobility, atomic force microscopy (AFM)
and contact angle () characterizations demonstrated that the porphyrin molecules can result in the formation of interfacial di-
pole layer between active layer and cathode. The interfacial dipole layer can obviously improve the open-circuit voltage (Voc
)
and charge extraction, and sequentially lead to the increase of PCE.
polymer solar cells, cathode interlayer, alcohol/water-soluble porphyrins
1
Introduction
voted to improving device efficiency by decreasing charge
collection/extraction barriers and forming ohmic contact
between electrode and active layer. Significant improve-
ments of PCE by placing a cathode interlayer between the
active layer and the metal electrode have been realized. It is
worth noting that certain alcohol/water-soluble organic or
polymeric electrolytes used as cathode interlayers can
strongly enhance the PCE of PSCs. Compared to other
cathode-interfacial-layer materials, the advantages of alcohol/
water-soluble organic or polymeric materials for PSCs are
remarkable due to their simple, vacuum-free, and environ-
mental friendly film formation during device fabrication
Bulk heterojunction (BHJ) solar cells based on active layers
comprised of conjugated polymers and fullerenes have at-
tracted great attention and are considered as promising de-
vices for an alternative energy source because of their light
weight, low cost, and flexibility [1,2]. The power-conver-
sion efficiency (PCE) of polymer solar cells (PSCs) larger
than 9% has been achieved [3,4].
To improve the PCE of PSCs, great deal of effort has
been invested in the synthesis of new materials [5–9], de-
vice structure optimization [10,11], and morphology modi-
fication of active layers [12]. Moreover, studies on the in-
terface between electrodes and active layers have been de-
[
3,4,13–17]. So far, most of the cathode interlayers with
high efficiency have been composed of polymers; small
organic molecule-based cathode interlayers that can effi-
ciently improve the performance of PSCs have been rare
[
18–20]. Compared to polymers, the advantages of small
*
Corresponding author (email: zhangjingy@jlu.edu.cn)
©
Science China Press and Springer-Verlag Berlin Heidelberg 2014
chem.scichina.com link.springer.com

2
Jia et al. Sci China Chem February (2015) Vol.58 No.2
molecules lie in their well-defined structures, consistent
high purity, and capacity for modification [21].
As a family of functional molecules, porphyrins have
important roles in both natural and synthesized systems due
to their excellent photophysical, semiconducting, electro-
chemical, and catalytic properties, as well as their stability
ternal standard. Elemental analyses were performed on a
flash EA 1112 spectrometer (Elementar, Germany). All
reagents and solvents, unless otherwise specified, were ob-
tained from Aldrich (USA) and Acros (Belgium) and used
as received. PCDTBT (Lot #YY6092C) was purchased
from 1-material Chemscitech Inc. (Canada). PC BM (Lot
71
[
22–27]. Recent investigations have focused on the applica-
#14A0021E1) was purchased from American Dye Source
(USA). All reactions were carried out using Schlenk tech-
niques under a nitrogen atmosphere.
tions of porphyrin-based materials in organic electronic
devices such as organic light-emitting devices (OLEDs)
[
28,29], organic photovoltaic devices (OPV) [30–37], or-
ganic field-effect transistors (OFETs) [38]. So far, in most
of these studies, the porphyrin compounds were applied to
active layers in organic electronic devices; their application
beyond active materials has been very limited [20]. There-
fore, exploration of the new applications and functions of
porphyrins in organic electronic devices shows great poten-
tial. In this contribution, several alcohol/water-soluble por-
phyrin molecules (Scheme 1) were employed as cathode
interlayers, which led to significant improvement of the
performance of polymer solar cells (PSCs).
2.1.1 Synthesis of zinc(II) meso-tetra(4-pyridyl) porphine
(Zn-TPyP)
H2-TPyP (200 mg, 0.32 mmol), zinc acetate (550 mg, 3
mmol) were dissolved in 500 mL dry DMF. Under nitrogen
atmosphere, the solution was stirred and heated to reflux for
5
h. After being cooled to room temperature, the solvent
was removed by vacuum evaporation; the crude product
was purified by alumina oxide chromatography with an el-
uent chloroform; and a purple powder was obtained. Yield:
1
1
31 mg (60%). H NMR (300 MHz, DMSO-d ):  9.02 (d,
6
J=6.0 Hz, 8 H), 8.85 (s, 8 H), 8.21 (d, J=6.0 Hz, 8 H). Anal.
calcd: C 70.44%, H 3.55%, N 16.43%; found: C 70.87%, H
2
Experimental
3
.36%, N 16.49%.
2
.1 Synthesis and characterization
2
.1.2 Synthesis of zinc(II) meso-tetra(N-methy-4-pyridyl)
1
porphine tetra-iodide (Zn-TPyPMeI)
H NMR spectra were measured on a Varian Mercury 300
MHz spectrometer (USA) with tetramethylsilane as the in-
A solution of Zn-TPyP (200 mg, 0.29 mmol) and methyl
Scheme 1 The structures of alcohol/water soluble porphyrins.

Jia et al. Sci China Chem February (2015) Vol.58 No.2
3
iodide (850 mg, 6 mmol) in 30 mL dry DMF was heated at
00 °C for 10 h. After being cooled to room temperature,
the solvent was removed by vacuum evaporation and the
was spin-cast from a mixed solvent of chlorobenzene/o-
dichlorobenzene (ratio=1:3). Porphyrins were dissolved in
water. First, PEDOT:PSS (Baytron PVP Al 4083) was spin-
coated onto a cleaned ITO and annealed in air at 120 °C for
10 min. Second, blend films of PCDTBT:PC71BM were
spin-cast from a solution of PEDOT:PSS and then annealed
in a glove box at 75 °C for 10 min. About 5 nm of cathode
interlayer was deposited onto the active layer by spin-
coating a porphyrin water solution (0.4 mg/mL); next 100
nm Al was evaporated as a cathode. For the electron-only
devices, Al was vacuum-deposited onto cleaned ITO as an
anode. Then the same procedures for the fabrication of
polymer solar cells described above were followed to com-
plete the counterparts. The active area of each device was
1
crude product was purified by recrystallization with metha-
nol and chloroform to obtain a black-brown powder. Yield:
1
3
43 mg (95%). H NMR (300 MHz, DMSO-d
6
):  9.43 (d,
J=6.6 Hz, 8 H), 9.10 (s, 8 H), 8.92 (d, J=6.6 Hz, 8 H), 4.73
s, 12 H). Anal. calcd: C 42.28%, H 2.90%, N 8.97%; found:
C 42.18%, H 2.88%, N 8.85%.
(
2
.1.3 Synthesis of zinc(II) meso-tetra[1-(1-adamantylme-
thyl ketone)-4-pyridyl]porphyrin tetra-bromide (Zn-TPyPA-
dBr)
A solution of Zn-TPyP (200 mg, 0.29 mmol) and 1-ada-
mantyl bromomethyl ketone (447 mg, 1.74 mmol) in 30 mL
dry DMF was heated at 100 °C for 12 h. After being cooled
to room temperature, the solvent was removed by vacuum
evaporation and the crude product was purified by recrystal-
lization with methanol and chloroform to obtain a black-
2
2.5×2.0 mm .
2
.3 Device characterizations
The current-density voltage (J-V) characteristics of the de-
1
brown powder. Yield: 445 mg (90%). H NMR (300 MHz,
vices were measured under N atmosphere in the glove box
2
DMSO-d ): 9.35 (d, J=6.6 Hz, 8 H), 9.07 (m, 24 H), 6.40
by using a Keithley 2400 (USA) both under illumination
and in the dark. The J-V and external quantum efficiency
(EQE) characteristics of all the devices were measured on a
Sciencetech (Canada) SSO-5K solar-spectrum-simulation
and device-measurement system. The simulated solar light
6
(
s, 8 H), 2.18 (s, 12 H), 2.13 (s, 24 H), 1.83 (s, 24 H). Anal.
calcd: C 61.78%, H 5.42%, N 6.55%; found: C 61.87%, H
5
2
.36%, N 6.49%.
.1.4 Synthesis of manganses(III) meso-tetra(4-pyridyl)
2
was calibrated to match 100 mW/cm AM 1.5G level by a
porphine (MnCl-TPyP)
standard monocrystalline silicon solar cell. All devices were
measured at ambient conditions. The J-V measurement
software was programmed with National Instrument (NI)
Labview 6.5 (USA) and the EQE was calculated directly by
software received from Sciencetech (Canada). In addition,
the static contact angles of the prepared surfaces were
measured with a commercial contact-angle system (Data-
Physics OCA 20, Germany) at ambient temperature using a
H2-TPyP (200 mg, 0.32 mmol) and manganese (II) chloride
(
234 mg, 1.86 mmol) were dissolved in 500 mL dry DMF.
Under nitrogen atmosphere, the solution was stirred and
heated to reflux for 8 h. After being cooled to room temper-
ature, the solvent was removed by vacuum evaporation and
the crude product was purified by alumina oxide chroma-
tography with an eluent chloroform to obtain a brown pow-
der. Yield: 163 mg (72%). Anal. calcd: C 67.95%, H 3.42%,
N 15.85%; found: C 67.98%, H 3.39%, N 15.84%.
4
µL water droplet as the indicator. AFM images were
measured with an S II Nanonaviprobe station 300 HV
Seiko, Japan) in contact mode.
(
2
.1.5 Synthesis of manganese(III) meso-tetra[1-(1-adam-
antylmethyl ketone)-4-pyridyl] porphyrin tetra-bromide
MnCl-TPyPAdBr)
(
3
Results and discussion
A solution of MnCl-TPyP (200 mg, 0.28 mmol) and 1-
adamantyl bromomethyl ketone (437 mg, 1.7 mmol ) in 30
mL dry DMF was heated at 100 °C for 12 h. After being
cooled to room temperature, the solvent was removed by
vacuum evaporation and the crude product was purified by
recrystallization with methanol and chloroform to obtain a
brown powder. Yield: 426 mg (88%). Anal. calcd: C
For comparison, two control devices were fabricated. One
was based on the active layer without any treatment. The
active layer of the other control device was treated with
water, which is the solvent of porphyrins. The water treat-
ment of the active layer was performed in a similar manner
as was used for the fabrication of the devices with cathode
interlayers. The contribution of the porphyrin rather than the
solvent to the improvement of PSCs was thus revealed.
PCDTBT:PC71BM blend films were employed as active
layers to prepare a set of devices (Figure 1) with the fol-
lowing structures.
6
6
0.89%, H 5.34%, N 6.46%; found: C 60.87%, H 5.36%, N
.49%.
2
.2 Device fabrication
The ITO glass substrates were precleaned carefully and
treated with plasma for 7 min. The blend ratio of PCDTBT:
PC71BM is 1:4 by weight and the active layer (35 mg/mL)
Device 1: [ITO/PEDOT:PSS/PCDTBT:PC BM/Al]
71
Device 2: [ITO/PEDOT:PSS/PCDTBT:PC BM/water/Al]
71

4
Jia et al. Sci China Chem February (2015) Vol.58 No.2
Figure 1 The structure of the PSC devices and the structures of materials
used in these devices.
Device 3: [ITO/PEDOT:PSS/PCDTBT:PC71BM/Zn-TPy-
PMeI/Al]
Device 4: [ITO/PEDOT:PSS/PCDTBT:PC71BM/Zn-TPy-
PAdBr/Al]
Device 5: [ITO/PEDOT:PSS/PCDTBT:PC71BM/MnClTPy-
PAdBr/Al]
Figure 2 presents the current density versus voltage (J-V)
characteristics of the devices under AM 1.5G illumination
2
at 100 mW/cm and in the dark. Figure 3 shows the external
quantum efficiency (EQE). Table 1 summarizes the open
circuit voltage (Voc), short circuit (Jsc), fill factor (FF), pow-
er conversion efficiency (PCE), series resistance (R
shunt resistance (Rsh) derived from the J-V characteristics
under illumination.
s
) and
Figure 2 The effect of different cathodes on PSCs performance. (a) J-V
characteristics of devices with the various cathodes at the surface of active
2
layer under 100 W/m AM 1.5G illumination; (b) J-V characteristics of the
five devices in the dark.
The devices with different cathode interlayers show a Voc
of 0.896 V for Device 3, 0.916 V for Device 4, and 0.927 V
for Device 5, which were higher than the control devices
Table 1 The performances of PCDTBT:PC71BM PSCs with the various
cathodes
(Voc=0.880 and 0.868 V for Device 1 and Device 2, respec-
Active layer
tively). The improvement of Voc can be mainly attributed to
the interlayer-induced decrease of work function (WF) of
the Al cathode. Ultraviolet photoemission spectroscopic
V
oc
J
sc
FF
PCE
R
s
R
sh
treatment
(Device-n)
None
2
2
2
(V) (mA/cm ) (%)
(%) (cm ) ( cm )
5.34
(5.26)
5.43
(5.40)
6.06
(6.04)
6.68
(6.61)
6.86
(6.79)
0
.868
10.95
10.87
11.27
11.47
11.91
56.2
56.8
60.0
63.6
62.1
15.7
14.1
11.5
7.1
505
606
787
968
980
(
Device-1)
Water
(UPS) measurements (Figure 4) demonstrated that the WF
of Al decreased upon the introduction of the porphyrin layer
onto the surface of the Al film. The WF values derived from
the UPS of the Al surface treated by different cathode inter-
layers were 3.51 eV for Zn-TPyPMeI, 3.42 eV for Zn-
TPyPAdBr, and 3.32 eV for MnCl-TPyPAdBr, whereas the
WF of the bare Al was 4.2 eV. Therefore, it was concluded
that porphyrin-based interlayers could lead to the WF de-
crease of the Al cathode. In addition, a MnCl-TPyPAdBr
interlayer is more efficient for minimizing the WF of Al.
Based on the electrochemical and absorption data the
HOMO energy levels (5.58 eV for Zn-TPyPMeI, 5.62 eV
for Zn-TPyPAdBr and 5.70 eV for MnCl-TPyPAdBr)
could be calculated.
0.880
(
Device-2)
Zn-TPyPMeI
(Device-3)
Zn-TPyPAdBr
0
0
0
.896
.916
.927
(
Device-4)
MnCl-TPyPAdBr
Device-5)
5.4
(
that the introduction of porphyrins between the active layer
and the Al cathode resulted in the improved PCE and the
contribution from the solvent (water) to the PSCs was rela-
tively smaller even though in Device 2, the solvent treat-
ment slightly improved both the VOC and FF. The resistanc-
es (R ) and shunt resistances (R ) (Table 1) were derived
s
sh
The PCE for the devices with cathode interlayers were
much higher than the control devices due to the simultane-
ous enhancement in Voc, Jsc, and FF (Table 1). It is obvious
from the J-V curves of the devices. Devices 3–5 with por-
phyrin interlayers had remarkably smaller R and larger R
compared with control Devices 1 and 2. Moreover, the
s
sh

Jia et al. Sci China Chem February (2015) Vol.58 No.2
5
2
2
1
1.31 mA cm for Zn-TPyPMeI, 11.42 mA cm for Zn-
2
TPyPAdBr and 11.82 mA cm for MnCl-TPyPAdBr, which
are in agreement with the PCE obtained from J-V character-
istics under illumination.
Simultaneous enhancement of Voc and Jsc resulted in in-
crease of FF for the optimized devices, which were 60.0%
for Device 3, 63.6% for Device 4, and 62.1% for Device 5.
The control Devices 1 and 2 showed much lower FF value
(
56.2% for Device 1 and 56.8% for Device 2). These results
demonstrated that the introduction of a porphyrin interlayer
improved the devices’ charge transport and extraction abili-
ties. To confirm this result, the J-V characteristics of single-
charge carrier devices with the following structures were
investigated:
Device 6: [ITO/Al/PCDTBT:PC71BM/Al]
Figure 3 EQE spectra of Devices 1–5.
Device 7: [ITO/Al/PCDTBT:PC71BM/water/Al]
Device 8: [ITO/Al/PCDTBT:PC71BM/Zn-TPyPMeI/Al]
Device 9: [ITO/Al/PCDTBT:PC71BM/Zn-TPyPAdBr/Al]
Device 10: [ITO/Al/PCDTBT: PC71BM/MnCl-TPyPAd-
Br/Al]
As shown in Figure 5, Devices 8–10 with cathode inter-
layers displayed significantly higher current densities than
Devices 6 and 7 without cathode interlayers. This result
means that the devices with a cathode interlayer have better
electron collection and transport properties. The electron
mobility can be measured in the space charge limited cur-
rent (SCLC) regime as described by Eq. (1):
2
3
J  9  V / 8L
(1)
0
r
where 
0
is the permittivity of free space; 
r
is the dielectric
constant of the active layer;  is the zero-field mobility; V
0
is the voltage drop across the device; and L is the active-

3
Figure 4 Ultraviolet photoelectron spectra of Al electrodes covered with
series cathode interlayers within the range of 16–19 eV.
layer thickness. The electron mobilities are 1.4810 (De-
3
3
vice 6), 1.6510 (Device 7), 2.8810 (Device 8), 7.64
(Device 9) and 6.8010 cm V s (Device 10). These
results were in agreement with the increasing trend of FF in
3
3
2
1
0
2
2
minimal R (5.4  cm ) and maximal Rsh (980  cm ) were
s
PSCs (Table 1).
recorded for Device 5, which ensured that Device 5 had
large Jsc. Device 5 with the MnCl-TPyPAdBr interlayer
displayed the highest PCE value (6.86%).
The J-V characteristics of the devices obtained under
dark conditions are presented in Figure 2(b). The dark cur-
rent densities of Devices 3–5 with cathode interlayers were
significantly suppressed, which implied that the built-in
potential (Vbi) across the device, which is the upper limit of
the attainable Voc in PSCs, drastically increased upon the
utilization of porphyrins cathode interlayers. Therefore, the
increase of Vbi should be responsible for the increase in VOC
in the devices with porphyrins as cathode interlayers. De-
vices 3–5 displayed noticeably higher Jsc compared with
control Devices 1 and 2. The improved PCE of the devices
with the different cathode interlayers were consistent with
the higher incident photon-to-current efficiency (IPCE)
values, which can be higher than 80% (Figure 3). The Jsc
values calculated from integration of the EQE spectra are
Figure 5 Experimental dark-current density-applied voltage (J-V) char-
acteristics of electron-only devices for the various cathodes.

6
Jia et al. Sci China Chem February (2015) Vol.58 No.2
Figure 6(a1–e1) shows the surface-morphology images
Images were collected with a digital camera. As shown in
Figure 6(a2–e2), the surfaces of pure PCDTBT:PC71BM
and PCDTBT:PC71BM treated by water were largely hydro-
phobic; their water contact angles were 99.18° and 97.05°,
respectively. This result indicates that water treatment only
slightly changed the surface polarity of PCDTBT: PC71BM.
By contrast, the surfaces of PCDTBT: PC71BM/ZnTPyP-
MeI, Zn-TPyPAdBr, and MnCl-TPyPAdBr were hydro-
philic, with respective contact angles of 74.75°, 74.17°, and
71.88°, which suggests accumulation of the ionic compo-
nent at the topmost organic surface.
The above results revealed accumulation of ionic com-
ponents at the topmost organic surface and a dipole layer on
the surface. The porphyrin-interlayer-induced decrease of
the WF of Al also demonstrated the formation of an interfa-
cial dipole layer. The detailed microscopic mechanism of
the interfacial dipole remains unclear. However, it is exten-
sively accepted that the interfacial dipole can improve the
charge transport, extraction, and Voc of solar cell [3,4,
obtained with atomic-force microscopy (AFM) measure-
ment at ambient conditions. The surface of the PCDTBT:
PC71BM BHJ film is relatively smooth, with a root-mean-
square (RMS) roughness of 0.89 nm (Figure 6(a1)). The
water-treated surface was slightly smoother than the pristine
film, with an RMS roughness of 0.78 nm, and remained
homogeneous as shown in Figure 6(a2). Therefore, the im-
provement of Voc and FF with water treatment is hardly re-
lated to the change of morphology. However, porphyrin-
treated surfaces of PCDTBT:PC71BM blend films show a
similar morphology. There are visible islands distributed
over the surface due to the self-aggregation of porphyrin
molecules and the RMS roughness are 1.36 nm for Zn-
TPyPMeI, 1.20 nm for Zn-TPyPAdBr and 1.30 nm for
MnCl-TPyPAdBr.
The surface polarity was studied by measuring the water-
contact angle () for the surfaces of PCDTBT:PC71BM,
PCDTBT:PC71BM/water and PCDTBT:PC71BM/porphyrins.
1
3–20]. Therefore, PCE increase should be mainly attribut-
ed to the formation of interfacial dipole layer in the solar
cell.
It is worth noting that Devices 4 and 5 showed better
performance than Device 3. A possible explanation for this
phenomenon is that in the porphyrin molecules of Zn-
TPyPAdBr and MnCl-TPyPAdBr, the relatively large hy-
drophobic adamant groups may enhance the wettability of
the porphyrin interlayer on the active layer, which is benefi-
cial to the charge transport from the active layer to the in-
terlayer. The device performance was sensitive to the
thickness of the cathode interlayer. The devices based on
the interlayer with thickness of 5 nm displayed the best
performance. When the thickness of the cathode interlayer
was less than 5 nm, the device performance was poor,
which should be attributed to the formation of discontinuous
layers of porphyrin. The cathode interlayer with thickness
of 7.5 nm was also employed to fabricate a device. Increas-
ing the thickness of the interlayer resulted in an obvious
decrease of the device’s performance. The thicker interlayer
may suppress charge transfer from the active layer to the
cathode [39,40].
4
Conclusions
In conclusion, three alcohol/water-soluble porphyrins (Zn-
TPyPMeI, Zn-TPyPAdBr, and MnCl-TPyPAdBr) have been
synthesized and successfully utilized in the PSCs with
PCDTBT:PC71BM as the active layer. Compared with the
two control devices, a simultaneous enhancement in Voc, Jsc
,
and FF of the PSCs with porphyrins as cathode interlayers
was achieved. A PCE of 6.86% for the device with
MnCl-TPyPAdBr interlayer was realized. This PCE value is
comparable with the best values of PCE of the PSCs cur-
rently reported, which indicates that MnCl-TPyPAdBr is a
Figure 6 AFM images and photos of water droplets on the surfaces of (a)
PCDTBT:PC71BM BHJ film, (b) PCDTBT:PC71BM BHJ film with water
treatment, (c) Zn-TPyPMeI on PCDTBT:PC71BM BHJ film, (d) Zn-
TPyPAdBr on PCDTBT:PC71BM BHJ film, (e) MnCl-TPyPAdBr on
PCDTBT:PC71BM BHJ film.

Jia et al. Sci China Chem February (2015) Vol.58 No.2
7
1
977–1983
promising candidate as a good cathode interlayer for highly
efficient PSCs. The porphyrin molecules can induce the
vacuum-level shift of an Al cathode via the formation of
permanent dipoles at the interface between active layer and
metal electrode. For porphyrin molecules, the structural
modifidation space is very large. Therefore, optimization of
porphyrin molecules should be an efficient strategy to de-
velop organic cathode interlayers for high-performance
polymer solar cells by modifing porphyrin molecules.
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