Efficient perovskite solar cells employing a solution-processable copper phthalocyanine as a hole-transporting material

Article abstract of DOI:10.1007/s11426-016-0393-5

The development of alternative low-cost and high-performing hole-transporting materials (HTMs) is of great significance for the potential large-scale application of perovskite solar cells (PSCs) in the future. Here, a facilely synthesized solution-processable copper tetra-(2,4-dimethyl-3-pentoxy) phthalocyanine (CuPc-DMP) via only two simple steps, has been incorporated as a hole-transporting material (HTM) in mesoscopic perovskite solar cells (PSCs). The optimized devices based on such a HTM afford a very competitive power conversion efficiency (PCE) of up to 17.1% measured at 100 mW cm^–2 AM 1.5G irradiation, which is on par with that of the well-known 2,2′,7,7′-tetrakis(N,N′-di-p-methoxyphenylamine)-9,9′-spirobifluorene (spiro-OMeTAD) (16.7%) under equivalent conditions. This is, to the best of our knowledge, the highest value reported so far for metal organic complex-based HTMs in PSCs. The advantages of this HTM observed, such as facile synthetic procedure, superior hole transport characteristic, high photovoltaic performance together with the feasibility of tailoring the molecular structure would make solution-processable copper phthalocyanines as a class of promising HTM that can be further explored in PSCs. The present finding highlights the potential application of solution processed metal organic complexes as HTMs for cost-effective and high-performing PSCs.

Full text of DOI:10.1007/s11426-016-0393-5

SCIENCE CHINA
Chemistry
March 2017 Vol.60 No.3:423–430
doi: 10.1007/s11426-016-0393-5
• ARTICLES •
Efficient perovskite solar cells employing a solution-processable
copper phthalocyanine as a hole-transporting material
Xiaoqing Jiang1, Ze Yu1*, Jianbo Lai1, Yuchen Zhang1, Ning Lei2,
Dongping Wang2* & Licheng Sun1,3*
1State Key Laboratory of Fine Chemicals, Institute of Artificial Photosynthesis, DUT-KTH Joint Education and Research Center on Molecular
Devices, Dalian University of Technology, Dalian 116024, China
2College of Chemical Engineering, Shenyang University of Chemical Technology, Shenyang 110142, China
3Department of Chemistry, School of Chemical Science and Engineering, KTH Royal Institute of Technology, Stockholm 10044, Sweden
Received September 28, 2016; accepted November 9, 2016; published online February 14, 2017
The development of alternative low-cost and high-performing hole-transporting materials (HTMs) is of great significance for the
potential large-scale application of perovskite solar cells (PSCs) in the future. Here, a facilely synthesized solution-processable
copper tetra-(2,4-dimethyl-3-pentoxy) phthalocyanine (CuPc-DMP) via only two simple steps, has been incorporated as
a hole-transporting material (HTM) in mesoscopic perovskite solar cells (PSCs). The optimized devices based on such a
HTM afford a very competitive power conversion efficiency (PCE) of up to 17.1% measured at 100 mW cm–2 AM 1.5G
irradiation, which is on par with that of the well-known 2,2′,7,7′-tetrakis(N,N′-di-p-methoxyphenylamine)-9,9′-spirobifluorene
(spiro-OMeTAD) (16.7%) under equivalent conditions. This is, to the best of our knowledge, the highest value reported so far for
metal organic complex-based HTMs in PSCs. The advantages of this HTM observed, such as facile synthetic procedure, superior
hole transport characteristic, high photovoltaic performance together with the feasibility of tailoring the molecular structure
would make solution-processable copper phthalocyanines as a class of promising HTM that can be further explored in PSCs. The
present finding highlights the potential application of solution processed metal organic complexes as HTMs for cost-effective
and high-performing PSCs.
solution-processable copper phthalocyanine, metal organic complex, low-cost, hole-transporting material,
perovskite solar cells
Citation:
Jiang X, Yu Z, Lai J, Zhang Y, Lei N, Wang D, Sun L. Efficient perovskite solar cells employing a solution-processable copper phthalocyanine as a
hole-transporting material. Sci China Chem, 2017, 60: 423–430, doi: 10.1007/s11426-016-0393-5
1 Introduction
solar energy is unarguably the largest exploitable sources that
potentially could be scaled up to meet the rising energy de-
mands due to the world population growth and economic de-
velopments. A very promising approach to capture solar en-
ergy is utilizing photovoltaic (PV) cells, which directly con-
vert solar energy to electrical energy. While the current PV
market is still dominated by the silicon-based solar cells, next
generation solar cell technologies fabricated through solu-
tion-processable techniques have emerged as cost-effective
alternatives to replace conventional solar cells [3].
Our society is facing a big technological challenge, devel-
oping abundant and renewable energy sources to meet the
rapidly increasing energy demands and to replace traditional
fossil fuels strongly correlated with climate and environmen-
tal concerns [1,2]. Among the various renewable alternatives,
*Corresponding authors (email: ze.yu@dlut.edu.cn; dpwang2015@163.com;
lichengs@kth.se)
© Science China Press and Springer-Verlag Berlin Heidelberg 2017
chem.scichina.com link.springer.com

424
Jiang et al. Sci China Chem March (2017) Vol.60 No.3
Recently, solution-processable organic-inorganic halide
flexibility, high hole mobility, excellent thermal and chem-
ical stability [31,32]. More intriguingly, the synthesis of
CuPc is quite simple, giving rise to rather low production
cost. Pristine CuPc has been successfully applied into PSCs
[33–35], showing excellent efficiencies of 16% together with
excellent long-term durability [35]. CuPc possesses a large
π-conjugated system which makes it difficult to dissolve
in most commonly used organic solvents. Therefore, this
complex has to be thermally evaporated under high vacuum
in these PSC devices. The thermal evaporation method is by
no means a desirable option, since it is highly energy-con-
suming, thus causing additional expenditure that counteracts
the merit of low production cost for CuPc. The solubility
of CuPc can be improved by introduction of substituents on
the periphery, thus to some extent increasing the distance
between the 18p electron conjugated system of CuPc and
facilitating the solubility [36]. However, PSC devices em-
ploying solution-processable based CuPcs as HTMs have
been rare up till now. Seok and co-workers [37] introduced
soluble tert-butyl substituted CuPc as an efficient dopant
for po-spiro-OMeTAD HTM, which resulted in a PCE of
19.4% for the spiro-OMeTAD based HTM (4.8 wt% doping
amount). Very recently, Lianos et al. [38] reported n-butyl
substituted CuPc as a solution-processable HTM in PSCs in
combination with mixed-halides perovskites, which achieved
a PCE of 8.5%.
Herein, solution-processable copper tetra-(2,4-dimethyl-
3-pentoxy) phthalocyanine (CuPc-DMP, Figure 1) has been
synthesized (Scheme 1) and incorporated as a HTM in
mesoscopic PSCs based on a (FAPbI3)0.85(MAPbBr3)0.15 light
absorber. PSC device using CuPc-DMP affords a very com-
petitive PCE of up to 17.1% at 100 mW cm–2 illumination
(AM 1.5G), which is on par with that of spiro-OMeTAD
(16.7%) measured under the same conditions. It is worth
emphasizing here that the synthesis of this new HTM only
involves two simple steps from commercially available start-
ing materials. This is the first example in PSCs employing
a metal organic complex-based HTM yielding an efficiency
reaching 17%.
perovskites with the composition ABX3 (A=CHNH3+ (MA),
3
NH=CHNH+ (FA) or Cs+; B=Pb or Sn; X=Cl, Br, I) have
3
received intense research attention as light absorbers in
solid-state solar cells due to some of their excellent proper-
ties, such as broad spectral absorption range, large absorption
coefficient, direct band gaps, high charge carrier mobility
and diffusion length [4–9]. The power conversion efficiency
(PCE) of perovskite solar cells (PSCs) has been rapidly
increased from a mere 3.8% in 2009 [10] to the current
record of 22.1% in April 2016 [11]. Considering the high
efficiency and facile fabrication process, PSC has shown a
great promise as a competitive low-cost solar cell to rival its
conventional inorganic counterparts.
The state-of-the-art PSC devices routinely employed hole-
transporting materials (HTMs), which play key roles in ex-
tracting and transporting the photo-generated holes from the
perovskites to the metal electrodes, and thus minimize unde-
sired recombination losses at the interfaces. Hence, searching
for an efficient HTM has been one of the hottest research top-
ics in PSCs. A wide range of HTMs have been developed and
incorporated into PSCs, including small molecular hole-con-
ductors [12–16], conducting polymers [17–21] and inorganic
p-type semiconductors [22–24]. Amongst these HTMs being
developed, spiro-OMeTAD has been the most widely used
HTM and has shown PCE of over 20% in conventional PSC
structures [25]. However, the synthesis of spiro-OMeTAD
is rather complicated, involving five reaction steps that re-
quire low temperature (–78 °C), and sensitive (n-butyllithium
or Grignard reagents) and aggressive (Br2) reagents. More-
over, high-performing devices require high-purity sublima-
tion-grade spiro-OMeTAD [26]. As a consequence, the price
of spiro-OMeTAD is considerably expensive (more than 10
times that of gold) [22], which significantly impedes its large-
scale application in the future. It is therefore of great impor-
tance to explore alternative HTMs exhibiting comparable or
even superior efficiencies relative to the widely used HTM
spiro-OMeTAD, but with more easily synthetic processes and
thus lower production costs.
With this regard, numerous novel small molecular hole-
conductors with facile synthesis routes have been developed
in PSCs [15,27]. However, the overall efficiencies of these
small molecular HTMs that can compete with the best effi-
ciencies spiro-OMeTAD reached have been rare. Only few
examples with two synthetic steps have shown efficiencies
beyond 16%, which can rival the well-known spiro-OMeTAD
[26,28–30].
It can be easily noticed that alternative high-performing
HTMs with facile synthesis routes developed so far have
been almost exclusively dominated by small molecular
hole-conductors. Metal organic complex copper phthalocya-
nine (CuPc) has been widely used as a p-type semiconductor
in organic thin film transistors and solar cells due to its
Figure 1 Chemical structure of CuPc-DMP.

Jiang et al. Sci China Chem March (2017) Vol.60 No.3
425
Scheme 1 Synthetic route of CuPc-DMP.
2 Experimental
The resulting solution was warmed to room temperature, and
stirred for 1 h. After the reaction, the reaction mixture was
poured into water (500 mL) and stirred for 1 h. The solid
formed was recovered by filtration and washed with water
(50 mL×3). This crude product was purified by column
chromatography on silica gel using CHCl3 as eluent to give
a white solid (4.83 g, 66% yield). 1H NMR (CDCl3, 500
MHz): 0.95 (d, 6H), 1.01 (d, 6H), 2.13 (m, 2H), 4.05 (t, 1H),
7.26 (d, 1H), 7.28(d, 1H), 7.57 (t, 1H).
2.1 Materials
PbI2 (>98%) was from TCI (Japan); PbBr2 (99%), HI (48%
in water), HBr (48% in water), CH3NH2 (33 wt% in absolute
ethanol), Formamidine acetate (99%) , 4-tert-butylpyridine
(TBP, 96%), Titanium diisopropoxide bis(acetylactonate)
75% in isopropanol (Tiacac) and Li-bis(trifluoromethane-
sulfonyl) imide (LiTFSI) were from Sigma-Aldrich (USA);
and mesoporous-TiO2 paste (18NR-T) were from Dyesol
(Australia). All chemicals used as received unless otherwise
2.2.2 Synthesis of CuPc-DMP
Following the literature [42], the mixture of 1 (3016.9 mg,
12.5 mmol), urea (1486.5 mg, 24.8 mmol), ammonium
molybdate (58.8 mg, 0.3 mmol), and copper(I) chloride
(297.0 mg, 3.0 mmol) in nitrobenzene (12 mL) was heated
at 160 °C for 12 h. Solvent was removed under reduced
pressure. The residue was purified by column chromatogra-
phy on silica gel using CHCl3/n-hexane (2:1, v/v) as eluent
to afford a blue-green powder (2.11 g, 68% yield). Anal.
Calcd. for (C60H72CuN8O4) (%): C, 69.77; H, 7.03; N, 10.85.
Found: C, 70.96; H, 7.24; N, 10.63.
stated. NH2CH=NHI (FAI) was synthesized according to
2
a reported procedure [39]. 30 mL hydroiodic acid (57% in
water) and 15 g formamidine acetate were reacted at 0 °C
for 2 h with stirring. The precipitates were recovered by
evaporating the solutions at 50 °C for 1 h. The products were
dissolved in ethanol, recrystallized using diethyl ether, and
finally dried at 60 °C in a vacuum oven for 24 h. Similarly,
CH3NH3Br (MABr) were prepared by reacting hydrobromic
acid (48 wt% in water) with methylamine according to
a reported procedure [25]. The mixed-cation perovskite
precursor solution of (FAPbI3)1–x(MAPbBr3)x (x=0.15) was
prepared in a glovebox, by dissolving the FAI (1 M), MABr
(0.2 M), PbI2 (1.1 M) and PbBr2 (0.2 M) in a mixed solvent of
dimethyl formamide (DMF) and dimethyl sulfoxide (DMSO)
(4:1, v/v) [40].
2.3 Device fabrication and characterization
Fluorine-doped tin oxide (FTO)-coated glass (NSG-Pilking-
ton, 15 Ω per square, Japan) was firstly patterned by etch-
ing with Zn powder and 2 M HCl. The etched substrate was
then sequentially cleaned by using detergent, de-ionized wa-
ter and ethanol. Remaining organic residues were removed
under oxygen plasma for 30 min. A compact TiO2 block-
ing layer (BL) of roughly 30–40 nm was deposited on the
cleaned FTO glasses by spray pyrolysis of titanium diiso-
propoxide bis(acetylacetonate) diluted in anhydrous ethanol
at a volumetric ratio of 1:10 and then heated at 500 °C for 30
min. A mesoporous TiO2 layer was deposited by spin-coat-
ing TiO2 paste (Dyesol 18NR-T, Australia) diluted in anhy-
drous ethanol at ratio of 1:5 by weight at 5000 r min–1 for
30 s. The layers were then sintered in air at 500 °C for
30 min. The mixed-cation perovskite films were deposited
onto the mesoporous TiO2/BL TiO2/FTO substrate substrates
2.2 Synthesis of CuPc-DMP
2.2.1 Synthesis of 3-(2,4-dimethyl-3-pentyloxy)phthaloni-
trile (1)
3-(2,4-Dimethyl-3-pentyloxy)phthalonitrile (1) was pre-
pared as described previously with some modifications [41].
Sodium hydride (1.92 g, 48 mmol, 60% dispersion in mineral
oil) was added portion-wise to a cooled DMF (30 mL, 0 °C)
under argon, and then 2,4-dimethyl-3-pentanol (4.53 g, 39
mmol) was added drop-wise, followed by stirring for 1 h. A
solution of 3-nitrophthalonitrile (5.19 g, 30 mmol) in DMF
(10 mL) was added slowly to the above solution over 1 h.

426
Jiang et al. Sci China Chem March (2017) Vol.60 No.3
from the precursor solution by a two-step spin-coating pro-
cedure, at 1000 r min–1 for 30 s and then 5000 r min–1 for
20 s. During the second step, 200 μL of chlorobenzene was
dropped onto the substrates 10 s prior to the end of the pro-
gram. Subsequently, the HTM layer was produced by spin-
coating the CuPc-DMP or spiro-OMeTAD solution on top of
the perovskite layer with a spin speed of 3000 r min–1 for
30 s. The CuPc-DMP or spiro-OMeTAD solutions were pre-
pared by dissolving 80 mg HTM, 30 μL 4-tert-butylpyridine
(TBP) and 20 μL lithium bis(trifluoromethanesulfonyl)imide
(LiTFSI) solution (520 mg LiTFSI in 1 mL acetonitrile) in
1 mL chlorobenzene. Finally, a layer of 100 nm Au was de-
posited on top of the HTM layer under high vacuum (<4×10–4
Pa) by thermal evaporation.
The photocurrent-voltage (J-V) characteristics of the solar
cells were measured using a Keithley 2400 Source-measure
unit (USA) under illumination of a simulated sunlight (AM
1.5G, 100 mW cm–2) provided by an Oriel Sol3A solar simu-
lator (Model: 94023A; Newport, USA) with an AM 1.5 filter
in ambient air. Light intensity was calibrated with a Newport
calibrated standard Si reference cell (SER; No 506/0358;
USA). A black mask with a circular aperture (0.09 cm2)
smaller than the active area of the square solar cell (0.20 cm2)
was applied on top of the cell. The J-V curves were obtained
from forward bias to short-circuit at a scan rate of 10 mV
S–1. For the measurements of hysteresis, the J-V curves were
obtained through forward scan (0–1.2 V) or reverse (1.2–0
V) at the rate of 10 mV S–1. The measurement of the incident
photon-to-current conversion efficiency (IPCE) was obtained
by a Hypermono-light (SM-25, Jasco Co. Ltd., Japan). Prior
to measurement, a standard silicon solar cell was used as
reference.
ture of FTO/PEDOT:PSS/CuPc-DMP/Ag, as reported previ-
ously [43]. For the hole-only devices, SCLC is described as
J(V)=9εε0μVV/8d3, where ε is the dielectric constant of the
material (normally taken to approach 3 for organic semicon-
ductors), μ is the hole mobility, V is the applied bias, and d
is the film thickness. Conductivity measurements were per-
formed as follows [43]. Plain glass substrates were sequen-
tially cleaned by detergent, de-ionized water and ethanol. Re-
maining organic residues were removed under oxygen plasma
for 30 min. A thin layer of mesoporous TiO2 was coated on
the glass substrates by spin-coating with a diluted TiO2 paste
(Dyesol 18NR-T, Australia) with terpineol (1:3, mass ratio).
The thickness of the film is ca. 500 nm, as measured with
a DekTak profilometer. After sintering the TiO2 film at 500
°C for 30 min, the film was cooled to room temperature. A
solution of HTM in chlorobenzene was spin-coated onto the
mesoporous TiO2 substrate, whereas the concentration was
the same as in case of the photovoltaic device. J-V character-
istics were recorded on a Keithley 2400 Source-measure unit
(USA).
3 Results and discussion
The synthesis of CuPc-DMP only involved two simple steps,
as shown in Scheme 1. 3-(2,4-Dimethyl-3-pentyloxy)ph-
thalonitrile was firstly prepared according to a previous
procedure with some modifications [41] (1H NMR spectrum
is shown in Figure S1, Supporting Information online).
Then, 3-(2,4-dimethyl-3-pentyloxy)phthalonitrile was mixed
with urea, ammonium molybdate and copper(I) chloride
in nitrobenzene. After purification, blue-green powder of
CuPc-DMP was finally obtained with a yield of 68%. More
detailed information on the synthesis can be found in the
Experimental Section.
2.4 Measurements
1H NMR spectrum was recorded on a Varian INOVA
500NMR apparatus (USA). Chemical shifts were calibrated
against tetramethylsilane (TMS) as an internal standard.
Cyclic voltammetry measurement was carried out with
CHI 630 Electrochemistry Work station. Redox poten-
tials of CuPc-DMP or Spiro-OMeTAD were conducted
in dichloromethane solution with 0.1 M TBAPF6 as the
supporting electrolyte. A glassy carbon electrode with a
surface area of 0.785 cm2 was used as working electrode.
The counter electrode consisted of a platinum wire and the
reference electrode was an Ag/AgNO3 electrode. The redox
potential was calibrated against Fc/Fc+ as an internal stan-
dard. The UV-Vis spectra were recorded an Agilent 8453
spectrophotometer (USA). Scanning electron microscopy
(SEM) was performed with FEI (Field Emission Instruments:
Nova Nano SEM 450, USA).
Normalized UV-Vis absorption spectrum of CuPc-DMP in
dichloromethane solution is depicted in Figure 2(a). CuPc-
DMP shows two intensive bands at 320 and 712 nm, corre-
sponding to B-band (also called the Soret-band) and Q-band,
respectively. The absorption spectrum of CuPc-DMP in the
thin film state is also displayed, which exhibits a slight red-
shift (~10 nm) of the maximum absorption of Q-band (inset of
Figure 2(a)). On the contrary, no significant absorption differ-
ence was observed for spiro-OMeTAD between the solution
and thin films states. It implies that there might be certain
amount of intermolecular π-π stacking in the thin film state
of CuPc-DMP, which is expected to facilitate a superior hole
mobility as reported previously [44,45].
Cyclic voltammetric measurements were performed to
evaluate the energy levels of this new HTM in comparison
to spiro-OMeTAD. The cyclic voltammograms of both the
HTMs were measured under the same conditions for a better
comparison, as displayed in Figure 2(b) for CuPc-DMP and
Hole mobility of HTMs was measured by using the space-
charge-limited current (SCLC) method with the device struc-

Jiang et al. Sci China Chem March (2017) Vol.60 No.3
427
Figure S2 for spiro-OMeTAD. The HOMO (highest occupied
molecular orbital) energy level is calculated from the oxida-
tion onset potential referenced against ferrocene/ferrocenium
(Fc/Fc+) [28]. Accordingly, the HOMO and LUMO (lowest
unoccupied molecular orbital) energy levels of CuPc-DMP
were estimated to be –5.46 and –3.82 eV (Table 1), analogous
to previously reported values [42]. The HOMO energy level
of CuPc-DMP matches well the low lying valence band (VB)
of perovskites (FAPbI3)0.85(MAPbBr3)0.15 [40]. It indicates
that CuPc-DMP should be capable of effectively extracting
holes from the perovskites.
limited currents (SCLC) method by using hole-only de-
vices as reported previously [43]. By fitting the J-V curves
(Figure 3(a)), the extracted hole mobility for pristine
CuPc-DMP is 9.8×10–5 cm2 V–1 S–1, which is considerably
higher than that of spiro-OMeTAD (4.0 × 10–5 cm2 V–1 S–1).
Hole transporting characteristics (mobility and conductiv-
ity) are very important parameters for HTM to effectively
transport/collect the photo-generated holes from the per-
ovskites. Hole mobility measurements were thus carried
out for pristine CuPc-DMP and spiro-OMeTAD. The hole
mobility of the HTM were estimated from a space-charge-
−
−
−
−
−
−
−
Figure 3 (a) J-V characteristics of pristine CuPc-DMP and spiro-OMeTAD
based hole-only devices; (b) conductivity characteristics of doped CuPc-
DMP and spiro-OMeTAD based devices; (c) thermal gravimetric analysis
of CuPc-DMP (color online).
Figure 2 (a) UV-Vis absorption spectra of CuPc-DMP and spiro-OMeTAD
in dichloromethane solutions and in the forms of thin films on the glass sub-
strates; (b) cyclic voltammetry (CV) of CuPc-DMP in dichloromethane so-
lution, potential vs. Ag/AgNO3 (color online).
Table 1 Electrochemical and optical parameters of CuPc-DMP and spiro-OMeTAD
c)
d)
e)
f)
HTM
λmax a) solution (nm)
λmax b) film (nm)
Eox (V)
0.66
EHOMO (eV)
ELUMO (eV)
Eg (eV)
CuPc-DMP
spiro-OMeTAD
712
385
722
385
–5.46
–5.13
–3.82
–2.17
1.64
2.96
0.33
a) Absorption spectra were measured in dichloromethane solutions; b) thin films were prepared by spin-coating chlorobenzene solutions on glass substrates;
c) cyclic voltammetry measurements were carried out in dichloromethane solutions with TBAPF6 (0.1 M) as supporting electrolyte, referenced against Fc/Fc+;
d) HOMO were determined by the equation EHOMO=–5.1–(Eox–E1/2(Fc/Fc+)); e) LUMO=HOMO+Eg; f) optical band gap was calculated by the onset of absorp-
tion.

428
Jiang et al. Sci China Chem March (2017) Vol.60 No.3
The conductivities of doped CuPc-DMP and spiro-OMeTAD
(the same compositions as used in the PSC devices, doped
with additives LiTFSI and TBP) were subsequently exam-
ined by using a two-contact electrical conductivity setup, the
curves of which are displayed in Figure 3(b) [43]. CuPc-DMP
also exhibits a much higher conductivity (6.62×10–5 S cm–1),
which is almost two times higher than that of spiro-OMeTAD
(2.24×10–5 S cm–1).
CuPc-DMP rivals the state-of-the-art HTM spiro-OMeTAD
with the same doping condition, which exhibits a maximum
PCE of 16.7% with a Voc of 1.05 V, a Jsc of 23.0 mA cm–2
and a FF of 0.69, respectively, as presented in Figure S3. It
is worth noting that the homo energy level of CuPc-DMP is
0.33 eV lower than that of spiro-OMeTAD from the cyclic
voltammetry (CV) measurements as listed in Table 1. Deeper
HOMO energy level is expected to result in a higher Voc, as
The thermal stability of CuPc-DMP was probed using ther-
mal gravimetric analysis (TGA) as shown in Figure 3(c). The
TGA shows that CuPc-DMP is quite stable and starts degrad-
ing only above 300 °C.
CuPc-DMP was further tested as a HTM in mesoscopic
PSCs and its photovoltaic properties were evaluated in com-
parison to spiro-OMeTAD. The schematic illustration and
cross-sectional SEM image of the device architecture are
depicted in Figure 4. The solar cell devices were fabricated
with a structure of FTO glass/compact TiO2/mesoporous
TiO2/perovskite/HTM/Au. The mixed-cation perovskite
light absorber (FAPbI3)0.85(MAPbBr3)0.15 was prepared by
using a solvent-engineering technique as reported previously
[39,40]. The resulting perovskite films were coated with
HTM CuPc-CMP via a solution process. More details of the
solar cell fabrication procedures and component parameters
are described in the Experimental Section.
Figure 5(a) displays the J-V characteristic of the cham-
pion cell using CuPc-DMP (doped with additives LiTFSI and
TBP) as a HTM measured under at 100 mW cm–2 illumi-
nation (AM 1.5G). A maximum PCE of 17.1% is achieved
for CuPc-DMP based device, with an open-circuit voltage
(Voc) of 1.04 V, a short-circuit current density (Jsc) of 23.2
mA cm–2 and a fill factor (FF) of 0.71. This PCE achieved by
Figure 5 (a) J-V characteristic of the PSC device based on doped CuPc-
DMP (inset: IPCE spectrum of the PSC device measured for (a)); (b) his-
togram of PCEs of 50 PSC devices using CuPc-DMP as HTMs; (c) PCE and
current density as a function of time under illumination at a fixed voltage of
0.8 V for PSC devices based on CuPc-DMP (color online).
Figure 4 (a) Schematic device architecture of perovskite solar cells studied;
(b) cross-sectional SEM image of the complete PSC device with CuPc-DMP
as a HTM (color online).

Jiang et al. Sci China Chem March (2017) Vol.60 No.3
429
the photovoltage of a PSC device is determined by the dif-
ference between the quasi Fermi levels of both the electron
and hole conducting materials. However, no significant dif-
ference of Voc values was observed for these two HTMs. One
likely reason should be mainly attributed to the lower lying
LUMO level of CuPc-DMP, which results in poorer electron
blocking ability as demonstrated by the previous report [37].
A slightly higher fill factor was found for the CuPc-DMP
based device, which should be mainly originated from the
much higher hole conductivity of this metal organic complex.
The IPCE spectrum (shown in the inset of Figure 5(a)) for
the CuPc-DMP based device displays a wide spectra response
to a long wavelength at around 840 nm, yielding a broad IPCE
plateau of over 85% in the range of 400 to 700 nm. The inte-
grated current density from the IPCE spectrum for the device
based on CuPc-DMP is calculated to be 22.0 mA cm–2, which
is basically in a good line with the measured value from the
J-V curve. Figure 5(b) shows the histogram of 50 identical
PSC devices employing CuPc-DMP, which exhibit good re-
producibility, yielding an average PCE of 15.1%. The repro-
ducibility of PSC devices based on spiro-OMeTAD (50 iden-
tical cells) was also investigated (Figure S3(b)), exhibiting an
analogous average PCE of 14.9%. The J-V hysteresis effects
for devices based on CuPc-DMP and spiro-OMeTAD were
also evaluated and the results are summarized in Figure S4
and Table S1 (Supporting Information online). Small hystere-
sis effects were observed for both of these two HTMs. The
hysteresis indexes are calculated to be 0.024 (CuPc-DMP)
and 0.054 (spiro-OMeTAD), respectively, according to a pre-
vious literature [46]. It was reported that the stabilized power
output is a reliable and scan-independent method to deter-
mine the efficiency of a PSC device [19]. Figure 5(c) dis-
plays the steady-state efficiency and current density of a rep-
resentative PSC device based on CuPc-DMP measured at a
constant bias of 0.8 V (close to maximum power point) over
180 s under 1 sun condition (AM 1.5G). CuPc-DMP based
device exhibits a steady-state efficiency of 15.1% and current
density of 18.9 mA cm–2 during the testing period. Stabilized
efficiency and current density for the spiro-OMeTAD based
device were also recorded as shown in Figure S5.
procedure, superior hole transport characteristic, high pho-
tovoltaic performance together with the feasibility of tailor-
ing the molecular structure would make solution-processable
copper phthalocyanines as a class of promising HTM that can
be further explored in PSCs. The present finding will def-
initely open up a new avenue for developing cost-effective
and highly efficient HTMs for large-area application of PSCs
in the future.
Acknowledgments This work was supported by the National Natural Sci-
ence Foundation of China (21606039, 21120102036, 91233201), the Na-
tional Basic Research Program of China (2014CB239402), the Swedish En-
ergy Agency, as well as the Knut and Alice Wallenberg Foundation.
Conflict of interest
The authors declare that they have no conflict of
interest.
Supporting information The supporting information is available online
at http://chem.scichina.com and http://link.springer.com/journal/11426.
The supporting materials are published as submitted, without typesetting
or editing. The responsibility for scientific accuracy and content remains
entirely with the authors.
1
Lewis NS, Nocera DG. Proc Natl Acad Sci USA, 2006, 103:
15729–15735
2
3
4
5
6
Service RF. Science, 2005, 309: 548–551
Yu Z, Li F, Sun L. Energy Environ Sci, 2015, 8: 760–775
Grätzel M. Nat Mater, 2014, 13: 838–842
Green MA, Ho-Baillie A, Snaith HJ. Nat Photonics, 2014, 8: 506–514
Chen W, Wu Y, Yue Y, Liu J, Zhang W, Yang X, Chen H, Bi E,
Ashraful I, Grätzel M, Han L. Science, 2015, 350: 944–948
Liu J, Shirai Y, Yang X, Yue Y, Chen W, Wu Y, Islam A, Han L. Adv
Mater, 2015, 27: 4918–4923
7
8
Kim HS, Lee CR, Im JH, Lee KB, Moehl T, Marchioro A, Moon SJ,
Humphry-Baker R, Yum JH, Moser JE, Grätzel M, Park NG. Sci Rep,
2012, 2: 591
9
Lee MM, Teuscher J, Miyasaka T, Murakami TN, Snaith HJ. Science,
2012, 338: 643–647
10 Kojima A, Teshima K, Shirai Y, Miyasaka T. J Am Chem Soc, 2009,
131: 6050–6051
11 http://www.nrel.gov/ncpv/images/efficiencychart.jpg
12 Jeon NJ, Lee HG, Kim YC, Seo J, Noh JH, Lee J, Seok SI. J Am Chem
Soc, 2014, 136: 7837–7840
13 Li H, Fu K, Hagfeldt A, Grätzel M, Mhaisalkar SG, Grimsdale AC.
Angew Chem Int Ed, 2014, 53: 4085–4088
14 Abate A, Paek S, Giordano F, Correa-Baena JP, Saliba M, Gao P,
Matsui T, Ko J, Zakeeruddin SM, Dahmen KH, Hagfeldt A, Grätzel
M, Nazeeruddin MK. Energy Environ Sci, 2015, 8: 2946–2953
15 Yu Z, Sun L. Adv Energy Mater, 2015, 5: 1500213
16 Qin P, Kast H, Nazeeruddin MK, Zakeeruddin SM, Mishra A, Bäuerle
P, Grätzel M. Energy Environ Sci, 2014, 7: 2981–2985
17 Heo JH, Im SH, Noh JH, Mandal TN, Lim CS, Chang JA, Lee
YH, Kim H, Sarkar A, Nazeeruddin MK, Grätzel M, Seok SI. Nat
Photonics, 2013, 7: 486–491
4 Conclusions
Solution-processable CuPc-DMP has been successfully in-
corporated as a HTM in mesoscopic PSCs. The optimized
device based on this HTM exhibits an impressive PCE of
17.1% under 100 mW cm–2 AM 1.5G illumination, which is
on par with the well-known spiro-OMeTAD under equiva-
lent conditions. However, by stark contrast to the compli-
cated synthesis procedure for spiro-OMeTAD, the synthesis
of CuPc-DMP is considerably easier, only involving two sim-
ple steps from commercially available raw materials. The
advantages of this HTM observed, such as facile synthetic
18 Zhu Z, Bai Y, Lee HKH, Mu C, Zhang T, Zhang L, Wang J, Yan H,
So SK, Yang S. Adv Funct Mater, 2014, 24: 7357–7365
19 Habisreutinger SN, Leijtens T, Eperon GE, Stranks SD, Nicholas RJ,
Snaith HJ. Nano Lett, 2014, 14: 5561–5568
20 Xiao J, Shi J, Liu H, Xu Y, Lv S, Luo Y, Li D, Meng Q, Li Y. Adv
Energy Mater, 2015, 5: 1401943

430
Jiang et al. Sci China Chem March (2017) Vol.60 No.3
21 Kwon YS, Lim J, Yun HJ, Kim YH, Park T. Energy Environ Sci, 2014,
7: 1454–1460
5: 3786–3791
34 Ke W, Zhao D, Grice CR, Cimaroli AJ, Fang G, Yan Y. J Mater Chem
A, 2015, 3: 23888–23894
22 Christians JA, Fung RCM, Kamat PV. J Am Chem Soc, 2014, 136:
758–764
35 Zhang F, Yang X, Cheng M, Wang W, Sun L. Nano Energy, 2016, 20:
108–116
23 Sepalage GA, Meyer S, Pascoe A, Scully AD, Huang F, Bach U,
Cheng YB, Spiccia L. Adv Funct Mater, 2015, 25: 5650–5661
24 Qin P, Tanaka S, Ito S, Tetreault N, Manabe K, Nishino H,
Nazeeruddin MK, Grätzel M. Nat Commun, 2014, 5: 3834
25 Bi D, Tress W, Dar MI, Gao P, Luo J, Renevier C, Schenk K,
Abate A, Giordano F, Correa Baena JP, Decoppet JD, Zakeeruddin
SM, Nazeeruddin MK, Gra tzel M, Hagfeldt A. Sci Adv, 2016, 2:
e1501170–e1501170
36 Aǧirtaş MS, Bekaroǧlu Ö. J Porphyr Phthalocya, 2001, 05: 717–720
37 Seo J, Jeon NJ, Yang WS, Shin HW, Ahn TK, Lee J, Noh JH, Seok SI.
Adv Energy Mater, 2015, 5: 1501320
38 Sfyri G, Chen Q, Lin YW, Wang YL, Nouri E, Xu ZX, Lianos P.
Electrochim Acta, 2016, 212: 929–933
39 Jeon NJ, Noh JH, Yang WS, Kim YC, Ryu S, Seo J, Seok SI. Nature,
2015, 517: 476–480
26 Gratia P, Magomedov A, Malinauskas T, Daskeviciene M, Abate A,
Ahmad S, Grätzel M, Getautis V, Nazeeruddin MK. Angew Chem Int
Ed, 2015, 54: 11409–11413
40 Correa Baena JP, Steier L, Tress W, Saliba M, Neutzner S, Matsui
T, Giordano F, Jacobsson TJ, Srimath Kandada AR, Zakeeruddin
SM, Petrozza A, Abate A, Nazeeruddin MK, Grätzel M, Hagfeldt A.
Energy Environ Sci, 2015, 8: 2928–2934
27 Ameen S, Rub MA, Kosa SA, Alamry KA, Akhtar MS, Shin HS, Seo
HK, Asiri AM, Nazeeruddin MK. ChemSusChem, 2016, 9: 10–27
28 Xu B, Bi D, Hua Y, Liu P, Cheng M, Grätzel M, Kloo L, Hagfeldt A,
Sun L. Energy Environ Sci, 2016, 9: 873–877
41 Chen Z, Xia C, Wu Y, Zuo X, Song Y. Inorgan Chem Commun, 2006,
9: 187–191
42 Chen CH, Cheng WT, Tsai ML, Huang KT. Ind Eng Chem Res, 2012,
51: 3630–3638
29 Bi D, Xu B, Gao P, Sun L, Grätzel M, Hagfeldt A. Nano Energy, 2016,
23: 138–144
43 Xu B, Sheibani E, Liu P, Zhang J, Tian H, Vlachopoulos N, Boschloo
G, Kloo L, Hagfeldt A, Sun L. Adv Mater, 2014, 26: 6629–6634
44 Liu J, Wu Y, Qin C, Yang X, Yasuda T, Islam A, Zhang K, Peng W,
Chen W, Han L. Energy Environ Sci, 2014, 7: 2963–2967
45 Cheng M, Xu B, Chen C, Yang X, Zhang F, Tan Q, Hua Y, Kloo L,
Sun L. Adv Energy Mater, 2015, 5: 1401720
30 Hua Y, Zhang J, Xu B, Liu P, Cheng M, Kloo L, Johansson EMJ,
Sveinbjörnsson K, Aitola K, Boschloo G, Sun L. Nano Energy, 2016,
26: 108–113
31 Zaumseil J, Sirringhaus H. Chem Rev, 2007, 107: 1296–1323
32 Xue J, Rand BP, Uchida S, Forrest SR. Adv Mater, 2005, 17: 66–71
33 Kumar CV, Sfyri G, Raptis D, Stathatos E, Lianos P. RSC Adv, 2015,
46 Kim HS, Park NG. J Phys Chem Lett, 2014, 5: 2927–2934