A bipolar small molecule based on indacenodithiophene and diketopyrrolopyrrole for solution processed organic solar cells

Article abstract of DOI:10.1039/c3ta13816j

A new linear A-D-A type low band gap small molecule (IDT-2DPP) based on 4,4,9,9-tetrakis(4-hexylphenyl)-4,9-dihydro-s-indaceno[1,2-b:5,6-b′] dithiophene (IDT) and 2,5-bis(2-ethylhexyl)-3,6-di(thiophen-2-yl)pyrrolo[3,4-c] pyrrole-1,4(2H,5H)-dione (DPP) was designed and synthesized by Pd-catalyzed Stille coupling reaction. IDT-2DPP exhibits good solubility and good thermal stability with a decomposition temperature of 395 °C. IDT-2DPP shows strong absorption from 500 to 700 nm with a high molar extinction coefficient of 1.3 × 10⁵ M^-1 cm^-1 at the absorption peak (640 nm) in chloroform solution. The HOMO and LUMO levels of IDT-2DPP were estimated to be -5.11 and -3.32 eV, respectively. Solution processed bulk-heterojunction solar cells using IDT-2DPP as a donor material blending with PC₇₁BM as an acceptor yielded a power conversion efficiency of 2.82%, and solar cells using IDT-2DPP as an acceptor material blending with P3HT as a donor yielded a power conversion efficiency of 0.83% with a high V _oc of 1.17 V.

Full text of DOI:10.1039/c3ta13816j

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A bipolar small molecule based on
indacenodithiophene and diketopyrrolopyrrole
Cite this: DOI: 10.1039/c3ta13816j
for solution processed organic solar cells†
Huitao Bai,ab Pei Cheng,ab Yifan Wang,ab Lanchao Ma,ab Yongfang Li,a Daoben Zhua
ac
*
and Xiaowei Zhan
A new linear A–D–A type low band gap small molecule (IDT-2DPP) based on 4,4,9,9-tetrakis(4-
hexylphenyl)-4,9-dihydro-s-indaceno[1,2-b:5,6-b0]dithiophene (IDT) and 2,5-bis(2-ethylhexyl)-3,6-
di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (DPP) was designed and synthesized by
Pd-catalyzed Stille coupling reaction. IDT-2DPP exhibits good solubility and good thermal stability with a
decomposition temperature of 395 ꢀC. IDT-2DPP shows strong absorption from 500 to 700 nm with a
high molar extinction coefficient of 1.3 ꢁ 105 Mꢂ1 cmꢂ1 at the absorption peak (640 nm) in chloroform
solution. The HOMO and LUMO levels of IDT-2DPP were estimated to be ꢂ5.11 and ꢂ3.32 eV,
respectively. Solution processed bulk-heterojunction solar cells using IDT-2DPP as a donor material
blending with PC71BM as an acceptor yielded a power conversion efficiency of 2.82%, and solar cells
using IDT-2DPP as an acceptor material blending with P3HT as a donor yielded a power conversion
efficiency of 0.83% with a high Voc of 1.17 V.
Received 23rd September 2013
Accepted 4th November 2013
DOI: 10.1039/c3ta13816j
www.rsc.org/MaterialsA
been designed and synthesized, and have achieved encouraging
PCEs up to over 8%.
1. Introduction
In recent years, an indaceno[2,1-b:6,5-b0]dithiophene (IDT)
Regarded as promising candidates for renewable energy sour-
ces, organic photovoltaic cells (OPV) have attracted consider-
able interest among scientic community because of their
advantages such as solution processability, low-cost, light-
weight and large area preparation.1–8 Over the last few decades,
great effort has been devoted to improving the power conver-
sion efficiency (PCE) of solution processed polymer solar cells
(PSCs). By optimizing polymer structure and device architec-
ture, PCEs of over 8% have been achieved based on polymer
donors and fullerene acceptors.9–15 To date, the highest PCE of
PSCs achieved is 10.6%.16
Small molecules possess some advantages over their poly-
mer counterparts such as well-dened structure, denite
molecular weight, simple synthesis, and high purity without
batch to batch variations.17–20 Recently, a variety of small
molecule donor materials containing triphenylamine,21–27
diketopyrrolopyrrole,28–32
silolo[3,2-b:4,5-b0]dithiophene37–40 and oligothiophenes41–44 have
unit has been attracting considerable attention due to its
excellent performance in constructing conjugated polymers for
organic eld-effect transistors (OFETs) and PSCs.45–51 Due to the
rigid and coplanar structure of the IDT unit, conjugated poly-
mers based on IDT exhibited strong intermolecular p–p inter-
action, which could enhance the p conjugation degree and lead
to high hole mobility.52 When applied in OPVs, IDT based low
band gap conjugated polymers exhibited broad absorption and
relatively high molar extinction coefficient, which is benecial
to obtaining high short circuit current (Jsc).53 Some IDT based
polymers have been synthesized and explored in OPV applica-
tion.52,54–56 PSCs based on blends of IDT polymer donors and
PC71BM acceptor yielded the best PCE of 7.51%.54 PSCs based
on blends of IDT polymer acceptors and poly(3-hexylthiophene)
(P3HT) donor yielded the best PCE of 1.18%.57 However, to our
knowledge, there has been only one report on IDT based small
molecules for application in OPVs as an electron donor,58 but no
report on IDT based small molecule electron acceptors.
benzo[1,2-b:4,5-b0]dithiophene,32–36
Diketopyrrolopyrrole (DPP) based semiconductors have been
exploited for OFETs and OPVs because of some advantages such
as good photochemical stability, excellent charge carrier
motilities and superior optical properties.59–61 The planar skel-
eton of DPP and its ability of readily forming hydrogen bonds
facilitate p–p stacking, which is benecial to obtaining high
mobilities.62,63 OPVs based on DPP polymers and small mole-
cules have exhibited PCEs as high as 6.5% (ref. 60 and 64) and
aBeijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Organic
Solids, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China.
E-mail: xwzhan@iccas.ac.cn
bUniversity of Chinese Academy of Sciences, Beijing 100049, China
cDepartment of Materials Science and Engineering, College of Engineering, Peking
University, Beijing 100871, China
† Electronic supplementary information (ESI) available: 1H NMR, 13C NMR and
XRD gures of IDT-2DPP. See DOI: 10.1039/c3ta13816j
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Scheme 1 Synthesis route for IDT-2DPP.
5.8%,32 respectively, when blending with fullerene acceptors. As
a versatile electron decient unit, DPP was also applied in
constructing small molecule acceptors.65,66 In our previous
work, a PCE of up to 2.05% was achieved when blending DPP
based acceptor DBS-2DPP with P3HT.66
In this paper, we designed and synthesized a novel bipolar
A–D–A type small molecule (IDT-2DPP, Scheme 1) based on IDT
as core and DPP as arms. IDT-2DPP exhibited broad and strong
absorption in the visible region. OPV devices based on the IDT-
2DPP:PC71BM blend exhibited the highest PCE of 2.82%. OPV
devices using IDT-2DPP as an acceptor and P3HT as a donor
were also fabricated, and achieved the highest PCE of 0.83%.
2.2. Fabrication and characterization of photovoltaic cells
Organic solar cells were fabricated with the structure: ITO/
PEDOT:PSS/IDT-2DPP:PC71BM/Ca/Al and ITO/PEDOT:PSS/
P3HT:IDT-2DPP/Ca/Al, respectively. The patterned indium tin
oxide (ITO) glass (sheet resistance ¼ 15 U ,ꢂ1) was pre-cleaned
in an ultrasonic bath of acetone and isopropanol, and treated in
an ultraviolet–ozone chamber (Jelight Company, USA) for
23 min.
A
thin layer (35 nm) of poly(3,4-ethyl-
enedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS, Bay-
tron PVP AI 4083, Germany) was spin-coated onto the ITO glass
and baked at 150 ꢀC for 20 min. IDT-2DPP:PC71BM (30 mg mLꢂ1
in total) or IDT-2DPP:P3HT (20 mg mLꢂ1 in total) in o-dichlo-
robenzene (DCB) solvent was spin-coated on the PEDOT:PSS
layer to form a photosensitive layer. Thermal annealing was
used aer spin-coating the active layer. A calcium (ca. 20 nm)
and aluminium layer (ca.100 nm) was then evaporated onto the
surface of the photosensitive layer under vacuum (ca. 10ꢂ5 Pa)
to form the negative electrode. The active area of the device was
4 mm2. The J–V curve was obtained with a computer-controlled
Keithley 236 Source Measure Unit. A xenon lamp coupled to AM
1.5G solar spectrum lters was used as the light source, and the
optical power at the sample was 100 mW cmꢂ2. The incident
photon to converted current efficiency (IPCE) spectrum was
recorded using a Stanford Research Systems model SR830 DSP
lock-in amplier coupled to a WDG3 monochromator and a
500 W xenon lamp. Hole-only or electron-only diodes were
fabricated using the architectures: ITO/PEDOT:PSS/active layer/
Au for holes and Al/active layer/Al for electrons. Mobilities were
extracted by tting the current density–voltage curves using the
Mott–Gurney relationship (space charge limited current).
2. Experimental section
2.1. Measurements and characterization
The 1H and 13C NMR spectra were recorded on a Bruker AVANCE
400 MHz and 600 MHz spectrometer using tetramethylsilane
(TMS; d ¼ 0 ppm) as an internal standard. Elemental analysis was
carried out using a FLASH EA1112 elemental analyzer. The mass
spectrum was recorded on a Bruker Daltonics BIFLEX III MALDI-
TOF Analyzer using MALDI mode. Solution (chloroform) and thin-
lm (on quartz substrate) UV-vis absorption spectra were recorded
on a JASCO V-570 spectrophotometer. Electrochemical measure-
ments were carried out under nitrogen on a deoxygenated solu-
tion of tetra-n-butylammonium hexauorophosphate (0.1 M) in
acetonitrile at a potential scan rate of 100 mV sꢂ1 using a
computer-controlled Zahner IM6e electrochemical workstation, a
glassy-carbon working electrode coated with IDT-2DPP lms,
a platinum-wire auxiliary electrode, and an Ag wire anodized with
AgCl as a pseudo-reference electrode. Potentials were referenced
to the ferrocenium/ferrocene (FeCp2+/0) couple by using ferrocene
as an external standard. Thermogravimetric analysis (TGA)
measurements were performed on a Shimadzu thermogravi-
metric analyzer (model DTG-60) under a nitrogen ow at a heating
rate of 10 ꢀC minꢂ1. Differential scanning calorimetry (DSC)
measurements were performed using a METTLER differential
scanning calorimeter (DSC822e) under nitrogen at a heating rate
of 10 ꢀC minꢂ1. X-ray diffraction (XRD) of thin lms was per-
formed in the reection mode at 40 kV and 200 mA with Cu-Ka
2.3. Materials
Unless stated otherwise, solvents and chemicals were obtained
commercially and were used without further purication.
Toluene was distilled from sodium–benzophenone under
nitrogen prior to use. Compound 1 (ref. 46) and compound 2
(ref. 29) were synthesized according to the literature.
2.4. Synthesis
radiation using a 2 kW Rigaku D/max-2500 X-ray diffractometer or To a three-necked round bottom ask were added compound 1
PANalytical B.V. Empyrean X-ray diffractometer. The nanoscale (123.3 mg, 0.1 mmol), compound 2 (132.6 mg, 0.22 mmol) and
morphology of the blend lm was observed by using a Veeco toluene (20 mL). The mixture was degassed with argon for 15
Nanoscopy V atomic force microscope (AFM) in tapping mode.
min, and then Pd(PPh3)4 (30 mg, 0.026 mmol) was added. The
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(m, 8H), 1.29 (m, 56H), 0.86 (m, 36H) (see Fig. S1 in the ESI†).
13C NMR (150 MHz, CDCl3): d 161.93, 161.67, 157.39, 153.94,
143.74, 142.30, 141.95, 141.40, 139.98, 139.78, 138.91, 136.86,
135.35, 135.21, 130.43, 130.09, 128.63, 128.53, 127.99, 127.87,
124.38, 121.15, 117.69, 108.37, 108.24, 63.27, 46.06, 39.33,
39.22, 35.71, 31.84, 31.46, 30.48, 30.36, 29.27, 28.69, 28.50,
23.82, 23.71, 23.20, 23.19, 22.72, 14.21, 14.14, 10.69, 10.64 (see
Fig. S2 in the ESI†). MS (MALDI-TOF): m/z 1953 (M+). Anal.
calcd for C124H150N4O4S6: C, 76.19; H, 7.68; N, 2.86. Found: C,
76.11; H, 7.90; N, 2.58%. lmax,s ¼ 640 nm (1.3 ꢁ 105 Mꢂ1 cmꢂ1).
3. Results and discussion
3.1. Synthesis and characterization
The synthetic route to IDT-2DPP is outlined in Scheme 1. Stille
coupling reaction of compound 1 with compound 2 afforded
Fig. 1 (a) TGA curve of IDT-2DPP and (b) DSC curve of IDT-2DPP.
mixture was reuxed for 24 h and then cooled to room
temperature. 5 mL aqueous KF (0.1 g mLꢂ1) solution was added
and stirred at room temperature overnight to remove the tin
impurity. 100 mL water was added and the mixture was
extracted with CHCl3 (2 ꢁ 100 mL). The organic phase was
dried over anhydrous MgSO4. Aer removing the solvent, the
residue was puried by column chromatography on silica gel
using petroleum ether–CHCl3 (1 : 2) as eluent yielding a blue
1
black solid (130 mg, 66%). H-NMR (400 MHz, CD2Cl2): d 8.90
(d, J ¼ 4 Hz, 2H), 8.83 (s, 2H), 7.60 (s, 2H), 7.48 (s, 2H), 7.32 (d,
J ¼ 4 Hz, 2H), 7.24 (m, 4H), 7.19 (d, J ¼ 8 Hz, 8H), 7.11 (d, J ¼ 8
Hz, 8H), 3.98 (m, 8H), 2.57 (t, J ¼ 8 Hz, 8H), 1.84 (m, 4H), 1.58
Fig. 3 (a) Cyclic voltammogram for IDT-2DPP in CH3CN–0.1 M
Bu4NPF6 at 100 mV sꢂ1; (b) the electronic energy level diagram of
P3HT, IDT-2DPP and PC71BM.
Table 1 Photovoltaic parameters of solar cells using IDT-2DPP as
donor and acceptor
Ratio
(wt%)
Jsc
FF
(%)
PCE
(%)
Blend
Voc (V)
(mA cmꢂ2
)
IDT-2DPP:PC71BM
IDT-2DPP:PC71BM
IDT-2DPP:PC71BM
IDT-
1 : 1
1 : 1.5
1 : 2
0.87
0.88
0.86
0.88
5.26
6.71
4.87
8.53
34.8
35.1
35.3
37.6
1.59
2.07
1.49
2.82
1 : 1.5
2DPP:PC71BMa
IDT-2DPP:P3HT
IDT-2DPP:P3HT
IDT-2DPP:P3HT
IDT-2DPP:P3HTa
1 : 0.8
1 : 1.2
1 : 1.8
1 : 1.2
1.13
1.13
1.15
1.17
0.78
1.05
0.66
1.43
36.5
38.2
36.8
49.5
0.32
0.45
0.28
0.83
Fig. 2 UV-vis absorption spectra of IDT-2DPP and P3HT in chloro-
form solution and in thin film. (The line with solid triangles represents
the P3HT solution; the line with hollow triangles represents the P3HT
film; the line with solid squares represents the IDT-2DPP solution; the
line with hollow squares represents the IDT-2DPP film.)
a
Annealing at 130 ꢀC for 15 min.
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3.2. Optical properties
The UV-vis absorption spectra of IDT-2DPP and P3HT were
recorded in chloroform solution (10ꢂ6 M) and in thin solid lm
and are shown in Fig. 2. IDT-2DPP exhibits strong absorption in
solution with a maximum molar extinction coefficient of 1.3 ꢁ 105
Mꢂ1 cmꢂ1 at 640 nm. IDT-2DPP shows a broader absorption band
in lm relative to that in solution. The optical band gap estimated
from the absorption edge (712 nm) of the thin lm is 1.74 eV. The
absorption peak of IDT-2DPP in thin solid lm is located at 620
nm, while the absorption peak of P3HT in thin solid lm is
located at 520 nm. The complementary absorption of IDT-2DPP
and P3HT is benecial to harvesting light in the visible region
when using IDT-2DPP as an acceptor to blend with P3HT.
3.3. Electrochemical properties
The electrochemical properties of IDT-2DPP were studied by the
cyclic voltammetry (CV) method with IDT-2DPP lms on glassy
carbon as working electrodes in acetonitrile solution containing
0.1 mol Lꢂ1 Bu4NPF6. IDT-2DPP exhibits irreversible oxidation
and quasi-reversible reduction waves (Fig. 3a). The highest
occupied molecular orbital (HOMO) and the lowest unoccupied
molecular orbital (LUMO) energy levels of IDT-2DPP are esti-
mated to be ꢂ5.11 and ꢂ3.32 eV from the onset oxidation and
reduction potentials, assuming the absolute energy level of
FeCp2+/0 to be 4.8 eV below vacuum. The electrochemical band
gap (LUMO–HOMO) estimated by CV is 1.79 eV, which is close
to the optical band gap (1.74 eV).
As shown in Fig. 3b, the LUMO gap (0.58 eV) and HOMO gap
(0.35 eV) between P3HT and IDT-2DPP and the LUMO gap
(0.68 eV) and HOMO gap (0.69 eV) between IDT-2DPP and
PC71BM are large enough to guarantee efficient exciton disso-
ciation. The difference between the HOMO of P3HT and the
LUMO of IDT-2DPP is as large as 1.44 eV, while the difference
between the HOMO of IDT-2DPP and the LUMO of PC71BM is
1.11 eV, which is benecial to obtaining a high open-circuit
voltage.
Fig. 4 (a) J–V characteristics of the solar cells based on IDT-2DPP/
PC71BM (1 : 1.5, w/w) and P3HT/IDT-2DPP (1.2 : 1, w/w) under the
illumination of AM 1.5G, 100 mW cmꢂ2; (b) the IPCE spectra. (The line
with solid squares represents the as-cast IDT-2DPP/PC71BM blend; the
line with hollow squares represents the annealed IDT-2DPP/PC71BM
blend; the line with solid triangles represents the as-cast P3HT/IDT-
2DPP (1.2 : 1, w/w) blend; the line with hollow triangles represents the
annealed P3HT/IDT-2DPP (1.2 : 1, w/w) blend.)
3.4. Photovoltaic properties
Bulk heterojunction (BHJ) solar cells were fabricated with a
typical sandwich structure of ITO/PEDOT:PSS/active layer/
Ca/Al by using IDT-2DPP as a donor or acceptor material to
IDT-2DPP in 66% yield. IDT-2DPP is soluble in common organic blend with the PC71BM acceptor or P3HT donor, respectively.
solvents such as dichloromethane, dichlorobenzene and chlo- Table 1 summarizes the detailed device characteristics at
roform at room temperature. The thermal properties of IDT- different donor/acceptor ratios with or without thermal
2DPP were investigated by TGA and DSC methods. The material annealing. Fig. 4 shows the J–V curves (a) and IPCE charac-
exhibits excellent thermal stability with a decomposition teristics (b) of four as-cast and annealed champion devices
temperature (Td, 5% weight loss) of 395 ꢀC in a nitrogen based on IDT-2DPP/PC71BM (1 : 1.5, w/w) and P3HT/IDT-
atmosphere (Fig. 1a). According to the DSC traces in Fig. 1b, 2DPP (1.2 : 1, w/w) under AM 1.5G illumination at an inten-
IDT-2DPP shows glass transition at ca. 100 C, and no melting sity of 100 mW cmꢂ2
.
ꢀ
peak from room temperature to 250 ꢀC, indicating that it is
The ratio of donor to acceptor slightly affects Voc and ll
amorphous. This result is also supported by the melting point factor (FF) but strongly affects the short circuit current density
measurement and X-ray diffraction (XRD) pattern of IDT-2DPP (Jsc). Before thermal annealing, the best PCE of 2.07% was
(see Fig. S3 in the ESI†). The phenyl alkyl substituents on the obtained at a ratio of 1 : 1.5 for the IDT-2DPP/PC71BM blend
IDT seem to hinder any proper alignment of this molecule, and 0.45% at a ratio of 1.2 : 1 for the P3HT/IDT-2DPP blend. The
making the lms amorphous.
PCEs for the IDT-2DPP/PC71BM (1 : 1.5, w/w) blend and for the
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P3HT/IDT-2DPP (1.2 : 1, w/w) blend were enhanced to 2.82% w/w) blend lms before and aer annealing are shown in Fig. 5.
ꢀ
and 0.83%, respectively, aer thermal annealing at 130 C for The IDT-2DPP/PC71BM blend lm exhibits a smooth and
15 min.
uniform surface before (Fig. 5a and b) and aer (Fig. 5c and d)
Atomic force microscope (AFM) tapping-mode images of thermal annealing in the height images.
IDT-2DPP/PC71BM (1 : 1.5, w/w) and P3HT/IDT-2DPP (1.2 : 1,
The P3HT/IDT-2DPP as-cast lm (Fig. 5e) exhibits a typical
cluster structure with many aggregated domains in the height
image, which decrease aer thermal annealing (Fig. 5g). In the
phase images, the as-cast blend lm exhibits a rough surface
(Fig. 5f), which becomes more smooth aer thermal annealing
(Fig. 5h); the RMS roughness decreases from 2.20 to 1.84 nm.
The space-charge limited current (SCLC) method was used to
measure hole and electron mobilities of the blends. Hole-only
and electron-only diodes were fabricated using the architec-
tures: ITO/PEDOT:PSS/IDT-2DPP:PC71BM (1 : 1.5, w/w) or
P3HT:IDT-2DPP (1.2 : 1, w/w)/Au for holes and Al/IDT-
2DPP:PC71BM (1 : 1.5, w/w) or P3HT:IDT-2DPP (1.2 : 1, w/w)/Al
for electrons. Fig. 6 shows the J–V curves for hole-only (a) and
electron-only (b) devices as-cast and annealed at 130 ꢀC for
15 min, and the detailed hole and electron mobility data are
summarized in Table 2.
Aer thermal annealing, the hole mobility of the IDT-2DPP/
PC71BM (1 : 1.5, w/w) blend lm slightly increases from 9.88 ꢁ
10ꢂ4 to 1.27 ꢁ 10ꢂ3 cm2 Vꢂ1 sꢂ1, while the electron mobility
slightly decreases from 2.94 ꢁ 10ꢂ4 to 1.82 ꢁ 10ꢂ4 cm2 Vꢂ1 sꢂ1
.
Fig. 5 AFM height images (3 mm ꢁ 3 mm) of (a) as-cast IDT-2DPP/ Fig. 6 J–V curves for (a) hole-only and (b) electron-only devices
PC71BM (1 : 1.5, w/w) blend films; (c) annealed IDT-2DPP/PC71BM based on IDT-2DPP/PC71BM (1 : 1.5, w/w) and P3HT/IDT-2DPP (1.2 : 1,
(1 : 1.5, w/w) blend films; (e) as-cast IDT-2DPP/P3HT (1 : 1.2, w/w) w/w) blend films as-cast and annealed at 130 ꢀC for 15 min. (The line
blend films; (g) annealed P3HT/IDT-2DPP (1.2 : 1, w/w) blend films. with solid squares represents the as-cast IDT-2DPP/PC71BM blend; the
AFM phase images (3 mm ꢁ 3 mm) of (b) as-cast IDT-2DPP/PC71BM line with hollow squares represents the annealed IDT-2DPP/PC71BM
(1 : 1.5, w/w) blend films; (d) annealed IDT-2DPP/PC71BM (1 : 1.5, w/w) blend; the line with solid triangles represents the as-cast P3HT/IDT-
blend films; (f) as-cast P3HT/IDT-2DPP (1.2 : 1, w/w) blend films; (h) 2DPP blend; the line with hollow triangles represents the annealed
annealed P3HT/IDT-2DPP (1.2 : 1, w/w) blend films.
P3HT/IDT-2DPP blend.)
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Table 2 SCLC data of hole-only and electron-only devices based on IDT-2DPP blends
Blend
Ratio (wt%)
Annealing (ꢀC)/time (min)
mh (cm2 Vꢂ1 sꢂ1
)
me (cm2 Vꢂ1 sꢂ1
)
IDT-2DPP:PC71BM
IDT-2DPP:PC71BM
IDT-2DPP:P3HT
IDT-2DPP:P3HT
1 : 1.5
1 : 1.5
1 : 1.2
1 : 1.2
As cast
130/15
As cast
130/15
9.88 ꢁ 10ꢂ4
1.27 ꢁ 10ꢂ3
6.76 ꢁ 10ꢂ4
1.58 ꢁ 10ꢂ3
2.94 ꢁ 10ꢂ4
1.82 ꢁ 10ꢂ4
1.11 ꢁ 10ꢂ5
8.16 ꢁ 10ꢂ5
For the P3HT/IDT-2DPP (1.2 : 1, w/w) blend lm, the hole 11 X. Li, W. C. H. Choy, L. Huo, F. Xie, W. E. I. Sha, B. Ding,
ꢂ1
mobility increases from 6.76 ꢁ 10ꢂ4 to 1.58 ꢁ 10ꢂ3 cm2 Vꢂ1
s
,
X. Guo, Y. Li, J. Hou, J. You and Y. Yang, Adv. Mater., 2012,
24, 3046–3052.
and the electron mobility also increases from 1.11 ꢁ 10ꢂ5 to
8.16 ꢁ 10ꢂ5 cm2 Vꢂ1 sꢂ1. The more smooth surface and more 12 T. Yang, M. Wang, C. Duan, X. Hu, L. Huang, J. Peng,
balanced charge transport are benecial to FF and PCE
enhancement aer thermal annealing.
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A new bipolar small molecule IDT-2DPP based on IDT and DPP 14 W. Li, A. Furlan, K. H. Hendriks, M. M. Wienk and
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and good thermal stability with a decomposition temperature of 15 L. Dou, J. You, J. Yang, C.-C. Chen, Y. He, S. Murase,
395 ꢀC. IDT-2DPP shows strong absorption from 500 to 700 nm
T. Moriarty, K. Emery, G. Li and Y. Yang, Nat. Photonics,
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with a high molar extinction coefficient of 1.3 ꢁ 105 Mꢂ1 cmꢂ1
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P3HT. The HOMO (ꢂ5.11 eV) and LUMO (ꢂ3.32 eV) levels of
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IDT-2DPP are also appropriate as a donor blending with PCBM
as an acceptor and an acceptor blending with P3HT as a donor. 17 Y. Lin, Y. Li and X. Zhan, Chem. Soc. Rev., 2012, 41, 4245–
Solution processed bulk-heterojunction solar cells based on 4272.
IDT-2DPP/PC71BM (1 : 1.5, w/w) yield the best PCE of 2.82% 18 A. Mishra and P. Bauerle, Angew. Chem., Int. Ed., 2012, 51,
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20 B. Walker, C. Kim and T.-Q. Nguyen, Chem. Mater., 2010, 23,
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21 S. Roquet, A. Cravino, P. Leriche, O. Aleveque, P. Frere and
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We thank the NSFC (21025418, 51261130582, 21021091), the 22 Q. Shi, P. Cheng, Y. Li and X. Zhan, Adv. Energy Mater., 2012,
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23 Y. Lin, P. Cheng, Y. Liu, Q. Shi, W. Hu, Y. Li and X. Zhan, Org.
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