Platinum(II) Complexes in Solar Cells
FULL PAPER
silane for 1H and 13C and an 85% H3PO4 external reference for 31P. UV/
Vis spectra were obtained on an HP-8453 diode array spectrophotometer.
Cyclic voltammograms were measured on a CHI model 600D electro-
chemistry station in THF containing 0.1m [Bu4N]PF6 as the supporting
electrolyte. A conventional three-electrode configuration consisting of a
platinum working electrode, a Pt-wire counter electrode and a Ag/AgCl
reference electrode was used. All of the potentials reported are quoted
with reference to the ferrocene/ferrocenium (Fc/Fc+) couple at a scan
and 40 nm gold films were evaporated on the surface of SiO2 through a
shadow mask as source and drain electrodes. The channel width (W) and
length (L) were 2.0 mm and 0.1 mm, respectively. Organic semiconduc-
tors were dissolved in toluene with a concentration of 10 mgmLꢀ1. The
solutions were stirred for 12 h at 608C and then spin-coated onto the sub-
strates, followed by thermal annealing (608C) process in a glovebox filled
with high purity N2.
The OFETs were characterized in the glovebox with a semiconductor pa-
rameter analyzer (Agilent 4156C). For transfer characteristics (ID ꢃVG),
the channel current (ID) between the source and drain was measured as a
function of gate voltage (VG) under a constant drain voltage. For output
characteristics (ID ꢃVDS), the channel current (ID) was measured as a
function of drain voltage (VDS) under a constant gate voltage (VG) and
different VG values resulted in different curves for ID versus VDS. The
field effect mobility of each transistor was calculated in the saturation
regime (VDS =ꢀ100 V) by plotting the square root of channel current
(ID) versus the gate voltage (VG) and fitting the curve by Equation(1), in
which Ci is the capacitance of the gate oxide with a unit area.
rate of 100 mVsꢀ1
X-ray crystallography: X-ray diffraction data were collected at 293 K
using graphite monochromated MoKa radiation (l=0.71073 ꢂ) on
.
a
Bruker Axs SMART 1000 CCD diffractometer. The collected frames
were processed with the software SAINT+[27] and an absorption correc-
tion (SADABS)[28] was applied to the collected reflections. The structure
was solved by direct methods (SHELXTL)[29] in conjunction with stan-
dard difference Fourier techniques and subsequently refined by full-
matrix least-squares analyses on F2. Hydrogen atoms were generated in
their idealized positions and all of the non-hydrogen atoms were refined
anisotropically. CCDC-833362 (PT4) contains the supplementary crystal-
lographic data for this paper. These data can be obtained free of charge
c.uk/data_request/cif. Crystal data for PT4: C56H68N4P2S6Pt Mw =1246.58,
pffiffiffiffiffi
ꢀ
ꢁ
2
2L
WCi dVG
d
ID
ð1Þ
m ¼
¯
triclinic, space group P1, a=10.2319(3), b=10.5176(3), c=13.7347(4) ꢂ,
General procedure for the synthesis of platinum(II) complexes: Under a
N2 atmosphere, each of the appropriate ethynyl ligands (L1–L4) and
trans-[PtCl2(PBu3)2] (0.49 equiv) were added to a mixture of Et3N and
a=92.897(2), b=98.372(2), g=96.858(2)8, V=1448.37(7) ꢂ3, Z=1,
1calcd =1.429 mgmꢀ3, m(MoKa)=2.733 mmꢀ1
, F(000)=636. 25502 reflec-
tions measured, of which 5101 were unique (Rint =0.0400). Final R1 =
0.0367 and wR2 =0.0948 for 4816 observed reflections with I>2s(I).
CH2Cl2 (1:1, v/v) in the presence of
a catalytic amount of CuI
(10 mol%). The reaction mixture was stirred at room temperature over-
night. The solvent was then removed under reduced pressure to obtain
the crude product. The mixture was purified by chromatography over a
silica column using the appropriate eluent to produce a pure sample of
PT1–PT4 in high yields (84–88%) after evaporation of the solvent and
drying in vacuo.
Compound PT1: Yield: 87%; dark red solid; 1H NMR (400 MHz,
CDCl3): d=7.94 (s, 2H, Ar), 7.84–7.81 (m, 4H, Ar), 7.79–7.77 (m, 2H,
Ar), 7.63–7.61 (m, 2H, Ar), 7.15–7.12 (m, 4H, Ar), 7.09–7.06 (m, 16H,
Ar), 2.76–2.72 (m, 4H, alkyl), 2.32 (s, 12H, Me), 2.20–2.16 (m, 12H,
alkyl), 1.73–1.69 (m, 4H, alkyl), 1.64–1.60 (m, 12H, alkyl), 1.57–1.49 (m,
12H, alkyl), 1.42–1.34 (m, 12H, alkyl), 0.99–0.95 (m, 18H, alkyl), 0.92–
0.88 ppm (m, 6H, alkyl); 13C NMR (100 MHz, CDCl3): d=154.09, 152.91,
148.27, 145.00, 143.41, 134.42, 132.99, 131.35, 130.00, 129.67, 128.86,
127.24, 126.02, 125.12, 124.81, 123.32, 121.76, 119.82 (Ar), 101.38, 77.28
DFT and TD-DFT computational methods: All of the calculations were
performed using the Gaussian 03 program package.[30] The DFT method
at the gradient-corrected correlation functional level PBE1PBE[31] was
used to optimize the ground-state geometries of PT1–PT4. The
PBE1PBE functional gave the best results in the simulations of the UV/
Vis properties by comparison of different functionals (B3LYP, BHandH-
LYP and MPWB1K). On the basis of the ground-state optimized geome-
tries, 50 singlet excited states for PT3 and PT4, and 60 singlet excited
states for PT1 and PT2 were calculated to determine the vertical excita-
tion energies using the TD-DFT method at the PBE1PBE level. The
LAN2DZ effective core potential basis set was applied for Pt atoms and
6-31G(d, p) for other atoms.
Fabrication and characterization of bulk heterojunction solar cells: The
device structure was ITO/PEDOT:PSS/active layer/LiF/Al, in which the
active layer is a blend film of the platinum(II)–bis(aryleneethynylene)
small molecule as the electron donor and PC70BM as the electron accept-
or in a weight ratio of 1:4 (w/w). Indium tin oxide (ITO) glass substrates
(10 W per square) were cleaned by sonication in toluene, acetone, etha-
nol, and deionized water, dried in an oven, and then cleaned with UV
ozone for 300 s. PEDOT:PSS (Baytron P AI 4083) was spin-coated onto
the pre-cleaned ITO substrate to form a 40 nm-thick layer, followed by
drying at 1208C for 30 min in air. Then, the substrates were transferred
to a glove box filled with nitrogen. The prepared solution containing a
mixture of PT1–PT4:PC70BM (1:4, by weight ratio) in chlorobenzene was
spin-coated on top of the PEDOT:PSS layer. Finally, the samples were
transferred into an evaporator where 1 nm of LiF and 80 nm of Al were
thermally deposited under vacuum at 10ꢀ6 Torr. The effective area was
0.12 cm2. The devices were encapsulated in the glove box and measured
in air.
ꢂ
(C C), 32.01, 30.66, 29.96, 29.51, 26.48, 24.43, 23.80, 22.81, 20.92, 14.24,
14.03 ppm (alkyl); 31P NMR (161.9 MHz, CDCl3): d=3.50 ppm (JP-Pt
=
2341 Hz); IR (KBr): v˜ =2080 cmꢀ1 (w, v(C C)); FAB-MS: m/z: 1793.1
[M]+; elemental analysis calcd (%) for C100H122N6P2PtS4: C 66.97, H 6.86,
N 4.69; found: C 67.10, H 6.64, N 4.78.
ꢂ
Compound PT2: Yield: 85%; purple solid; 1H NMR (400 MHz, CDCl3):
d=8.08–8.07 (m, 2H, Ar), 7.94 (s, 2H, Ar), 7.81–7.79 (m, 2H, Ar), 7.73–
7.71 (m, 2H, Ar), 7.53–7.51 (m, 4H, Ar), 7.29–7.28 (m, 2H, Ar), 7.10–
7.02 (m, 20H, Ar), 2.76–2.72 (m, 4H, alkyl), 2.32 (s, 12H, Me), 2.20–2.17
(m, 12H, alkyl), 1.73–1.69 (m, 4H, alkyl), 1.67–1.59 (m, 12H, alkyl),
1.54–1.49 (m, 12H, alkyl), 1.42–1.35 (m, 12H, alkyl), 0.99–0.95 (m, 18H,
alkyl), 0.92–0.89 ppm (m, 6H, alkyl); 13C NMR (100 MHz, CDCl3,): d=
152.68, 147.93, 145.32, 144.95, 143.53, 137.86, 134.34, 132.93, 129.99,
129.05, 128.35, 127.21, 126.78, 126.47, 126.00, 125.33, 124.88, 124.54,
ꢂ
122.96, 122.28 (Ar), 101.49, 100.00 (C C), 32.01, 30.65, 29.95, 29.51,
26.47, 24.43, 23.80, 22.81, 20.91, 14.23, 14.03 ppm (alkyl); 31P NMR
Current–voltage characteristics were measured using a computer con-
trolled Keithley 236 source meter. The photocurrent was measured under
AM 1.5G illumination at 100 mWcmꢀ2 from a solar simulator (Oriel,
91160 A-1000). The EQE was measured at a chopping frequency of
275 Hz with a lock-in amplifier (Stanford, SR830) during illumination
with the monochromatic light from a xenon lamp. The AFM measure-
ments were performed on a SPA300HV instrument with an SPI3800 con-
troller (Seiko Instruments). The images were taken with the tapping
mode.
(161.9 MHz, CDCl3): d=3.51 ppm (JP-Pt =2335 Hz); IR (KBr): v˜ =
+
2078 cmꢀ1 (w, v(C C)); FAB-MS: m/z: 1956.7 [M] ; elemental analysis
ꢂ
calcd (%) for C108H126N6P2PtS6: C 66.26, H 6.49, N 4.29; found: C 66.37,
H 6.65, N 4.34.
Compound PT3: Yield: 84%; dark red solid; 1H NMR (400 MHz,
CDCl3): d=8.07–8.05 (m, 2H, Ar), 7.74–7.72 (m, 2H, Ar), 7.52–7.50 (m,
4H, Ar), 7.48–7.46 (m, 2H, Ar), 7.29–7.27 (m, 2H, Ar), 7.09–7.06 (m,
8H, Ar), 7.04–7.01 (m, 12H, Ar), 2.36–2.33 (m, 12H, Bu), 2.32 (s, 12H,
Me), 1.69–1.66 (m, 12H, Bu), 1.49–1.44 (m, 12H, Bu), 0.93–0.87 ppm (m,
18H, Bu); 13C NMR (100 MHz, CDCl3): d=156.81, 152.22, 147.85,
144.99, 144.82, 138.34, 132.89, 130.14, 130.00, 127.93, 127.37, 126.44,
Fabrication and characterization of organic field-effect transistors
(OFETs): Silicon wafers (n-type) with a thermal oxide layer (500 nm)
were used as the substrates. The 5 nm chromium (as an adhesion layer)
Chem. Eur. J. 2012, 18, 1502 – 1511
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1509