Applying Thienyl Side Chains and Different Ï-Bridge to Aromatic Side

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Applying Thienyl Side Chains and Different #-bridge to Aromatic Side-Chain Substituted Indacenodithiophene-based Small Molecule Donors for High-Performance Organic Solar Cells Jin-Liang Wang, Kai-Kai Liu, Sha Liu, Feng Liu, Hongbin Wu, Yong Cao, and Thomas P. Russell ACS Appl. Mater. Interfaces, Just Accepted Manuscript • Publication Date (Web): 23 May 2017 Downloaded from http://pubs.acs.org on May 25, 2017

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ACS Applied Materials & Interfaces

Applying Thienyl Side Chains and Different π-bridge to Aromatic Side-Chain Substituted Indacenodithiophene-based Small Molecule Donors for HighPerformance Organic Solar Cells Jin-Liang Wang,* ,†,§ Kai-Kai Liu, †,§ Sha Liu, ‡,§ Feng Liu,* , # Hong-Bin Wu,*, ‡ Yong Cao ‡ and Thomas ＄

P. Russell ＄ †

Beijing Key Laboratory of Photoelectronic/Electrophotonic Conversion Materials, Key Laboratory of

Cluster Science of Ministry of Education, School of Chemistry and Chemical Engineering, Beijing Institute of Technology, Beijing, China. ‡

Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent

Materials and Devices, South China University of Technology, Guangzhou, China #

Department of Physics and Astronomy, and Collaborative Innovation Center of IFSA (CICIFSA),

Shanghai Jiaotong University, Shanghai 200240, P. R. China ＄

Department of Polymer Science and Engineering, University of Massachusetts, Amherst, USA

KEYWORDS: organic solar cells, small molecules donor materials, structure-property relationship, solvent vapor annealing, selenophene π-bridge

ABSTRACT: A pair of linear tetrafluorinated small molecular donors, named as ThIDTTh4F and ThIDTSe4F, which are with tetrathienyl-substituted IDT as electron-rich central core, electron-deficient difluorobenzothiadiazole as acceptor units, and donor end-capping groups, but having differences in the π-bridge (thiophene and selenophene), were successfully synthesized and evaluated as donor materials in organic solar cells. Such π-bridge and core units in these small molecules play a decisive role in the formation of the nanoscale separation of the blend films, which were systematically investigated through absorption spectra, grazing incidence X-ray diffraction pattern, transmission electron microscopy images, resonant soft X-ray scattering profiles, and charge mobility measurement. The ThIDTSe4F (with selenophene π-bridge)-based device exhibited superior performance than devices based on ThIDTh4F

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(with thiophene π-bridge) after post annealing treatment owing to optimized film morphology and improved charge transport. Power conversion efficiency of 7.31% and fill factor of ca. 0.70 were obtained by using a blend of ThIDTSe4F and PC71BM with thermal annealing and solvent vapor annealing treatments, which is the highest PCE from aromatic side-chain substituted IDT-based small molecular solar cells. The scope of this study is to reveal the structure-property relationship of the aromatic sidechain substituted IDT-based donor materials as a function of π-bridge and the post annealing conditions.

INTRODUCTION During the past two decades, bulk-heterojunction organic solar cells have received extensive research interesting owing to their applications in light-weight, flexible, and lost cost large-area photovoltaic devices.1-6 One of the key components of these devices is the donor materials, which contributed most to harvest solar energy. Therefore, extensive efforts have been devoted to develop conjugated polymers-based bulk-heterojunction organic solar cells, which showed rapid process with the PCE of around 12%.7-12 However, the uncertain molecular weight of polymers have led

to the batch-to-batch variation of the electronic properties of the polymeric active

materials. On the other hand, structurally-precise small molecular donors are very promising alternative to polymer counterpart, which provided certain advantages over polymers, including less batch to batch variations and higher levels of purity.13-16 Moreover, the absorption spectra, electronic energy levels, carrier mobility and structural ordering of small molecular system can be easily tailored by various of D, A, and π-bridge. As a result, these small molecular materials showed broad and strong absorptions, low-lying HOMO energy levels, high hole mobilities, and desirable molecular stacking mode. These features have contributed to create highly efficient small molecular system and to understand the relationships of structure-device performance.17-23 Currently, the popular strategy for high efficient small molecular donor was based on oligothiophene/benzodithiophene (BDT) or other electron-rich units as core and capped with relatively electron-withdrawing units, which was called as “A-D-A” sequence system. Chen and


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other groups did outstanding research work in A-D-A sequenced small molecules with the PCEs of over 10%.24-30 Recently,

D-A-D-A-D sequenced small molecules, that can be viewed as

modified A-D-A sequenced small molecules by further end-capping of donor terminal units, have attracted much attention. It is critical to note that most of D-A-D-A-D structure small molecules do not readily achieve comparable PCE even upon careful device optimizations in comparison with these of “A-D-A” typed system.31-36 Thus the molecular structural optimization of D-A-D-AD sequenced small molecules with novel building blocks are the most important factor associating with high PCE small molecular donor. Recently, ladder-type indacenodithiophene (IDT) donor core has emerged as one of the most popular electron-rich repeating units for highly efficient organic solar cells.37-39 The record PCEs of ca. 7% have been achieved using IDT-based conjugated polymer as donor materials in BHJOSCs.40 However, tetraphenyl-substituted indacenodithiophene-based small molecules donor materials showed only moderate PCE (ca. 5%) with low FF (< 0.5) in BHJ-OSCs.41-44 Although the four bulky rigid phenyl substituents on IDT backbone do not disrupt the planarity of the IDT core, they may lead to weak intermolecular interactions and low charge transport ability, thus results in undesired film morphology and charge recombination in organic solar cells. In general, minor changes in the chemical structure and packing of backbone and side-chain impact the film morphology and materials photovoltaic performance to a significant extent.45-47 For example, comparing to phenyl side-chains, thienyl side chain might increase intermolecular interactions and charge mobility due to stronger sulfur-sulfur interaction.48 Besides, the aromatic side chains engineering showed a critical role in improving the miscibility with other materials and crystallinity in the blend films, which could significantly improve device performance when the conjugated backbone is completely same.49-50 With these considerations, we think that thienyl side chain functionalized indacenodithiophene-based small molecular donor would be an interesting strategy for achieving high performance organic solar cells. However, there is rarely reported



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small molecular donor materials based on thienyl side unit functionalized indacenodithiophene. Moreover, a fundamental understanding of the relationship between structure-molecular aggregates and device performance based on such donor molecules remains to be explored.

Chart 1: Chemical structures of two small-molecules ThIDTTh4F and ThIDTSe4F.

Here, we reported the design and synthesis of a pair of tetrafluorinated small molecular donor ThIDTTh4F and ThIDTSe4F (Chart 1), which both have same tetrathienyl-substituted IDT (ThIDT) as electron-rich central core, same difluorobenzothiadiazoles as electron-deficient units, and same end-capping groups, except for having different π-bridge. Attention is paid to the influence of the ThIDT core and the thiophene/selenophene ring π-bridge on the resultant photovoltaic properties. Therefore, π-bridge dependence of the electrochemical properties of the thin films, charge transport properties of blend films, and the photovoltaic performance of two ThIDT core-based small molecules were systematically investigated using photovoltaic device characterization, absorption spectra of blend films, TEM images, grazing incidence X-ray diffraction, resonant soft X-ray scattering profile, and charge mobility data. Because these small molecules was installed many alkyl group on the backbone, they exhibited good solubility in common organic solvents such as CHCl3, toluene, and chlorobenzene and thus can readily be


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solution-processed and form excellent smooth films by spin-coating. As a result of optimized film morphology and charge transport by solvent vapor annealing treatment or combined thermal annealing and solvent vapor annealing treatment, the best PCE of 7.31% were achieved for these devices using ThIDTSe4F:PC71BM blends. Such PCE is the highest PCE for solution-processed organic solar cells from small donor molecules with aromatic side-chain substituted IDT donor core and comparable to the best PCEs based on D-A-D-A-D sequenced small molecules in BHJOSCs. In contrast, its counterpart ThIDTTh4F with thiophene π-bridge achieved only modest device efficiencies after SVA treatment. Importantly, we emphasized the correlation of molecular structure and post-annealing treatments on BHJ-OSCs performance for ThIDT-based small molecules, and hence provides a guideline for further designing highly efficient D-A-D-A-D sequenced small molecules for organic solar cells.

RESULITS AND DISCUSSION Scheme 1 outlines the synthetic routes to the D-A-D-A-D sequenced small molecules ThIDTTh4F and ThIDTSe4F with different π-bridge and detailed experimental procedures are showed in the experimental sections. 1 was synthesized according to literature by Stille crosscoupling reaction from Dimethyl-2,5-dibromoterephthalate

and 5-(trimethylsilyl)-2-(tri-n-

butylstannyl)-thiophene.51 2-ethylhexylthiophene was lithiated by n-BuLi and then was quenched by 1 to make diol 2 and was used in the next step without any further purification. The 2ethylhexyl thienyl side chains functionalized IDT 3 (ThIDT) was then made via intramolecular acid catalyzed Friedel-Crafts cyclization (the TMS group was removed during the reaction). Treatment of 3 with N-bromosuccinimide (NBS) gave 4 in 95% isolated yield. Lastly, ThIDTTh4F was prepared as a dark solid by a symmetrical cross-couplings between 4 and stannylated intermediate 5 with thiophene as π-bridges

52

in 74% isolated yield. In parallel,

intermediate 7 was obtained by an asymmetrical cross-couplings between 666 and 2tributyltinselenophene in 91% isolated yield. 7 was lithiated by LDA and then quenched by



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Me3SnCl to afford 8 with selenophene as π-bridges. Finally, stannylated intermediate 8 was reacted with the dibromide 4 to afford ThIDTSe4F in 78% isolated yield. All key intermediates, ThIDTTh4F, and ThIDTSe4F were purified by flash column chromatography, and their structures and purity were characterized by NMR spectroscopy and MALDI-TOF MS. Under N2 atmosphere, thermogravimetric analysis (TGA) of ThIDTTh4F and ThIDTSe4F showed that both of the onset temperature with 5% weight-loss were over 400oC (Figure S1), which is enough for device application.

Meanwhile, solid phase transition properties were measured by

differential scanning calorimetry (DSC). Upon the heating process, we can find that characteristic phase transition behaviour are in the range of 210-220 oC for ThIDTTh4F and 170-190 oC for ThIDTSe4F. The obvious phase transition behaviour of ThIDTSe4F might indicated that crystalline character of ThIDTSe4F.

S

COOCH3

TMS

S S

S

TMS

H3COOC

S

TMS

n-BuLi, THF, -78 oC to rt

S

HO

F

S

S

S Br

Br

S S

S

S 4

3

S

S N

S

R S

4

S

2

F

N-bromosuccinimide, THF, DMF, rt, 2 h

S

TMS

S

S

S

S

1

Sn

S

HCl/AcOH, 80 oC, 12 h

OH

S

N

F

5 R

S

Pd2(dba)3, P(o-tolyl)3, Toluene, reflux, 12 h

S

F

N S

S

S N

S

S N

F

S

R S

S

S

S

S

F

F

N

S

S

S

Br R N

F

S

2-tributyltinselenophene, Pd2(dba)3, P(o-tolyl)3, Toluene, reflux, 12 h

N 6

R = n-C6H13 ThIDTTh4F F

o

F S

Se N

S

N

7

S

R a) LDA, -78 C, 1 h. b) (CH3)3SnCl, -78 o C to rt, 10 h

F F

F

R S

Sn

Se N

S

N

8

S

R

S

4, Pd2(dba)3, P(o-tolyl)3, Toluene, reflux, 12 h

S

F

N S

S S

S N

S N

S

S

N S

Se

Se

S

F

S F

ThIDTSe4F

Scheme 1. Synthesis of ThIDTTh4F and ThIDTSe4F. Figure 1 showed absorption spectra of two small molecules ThIDTTh4F and ThIDTSe4F in diluted solutions and thin-films. Two small molecules both showed a main absorption band across


R

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from 500 to 800 nm in solutions and in thin film because of the intramolecular charge transfer of conjugated backbone. The absence of shoulders in the main absorption band of two molecules indicated both of materials did not form aggregation at the diluted solution. In solution, the absorption maximum peak was located at 554 nm for ThIDTTh4F with thiophene as a spacer. After changing the spacer with selenophene ring, the maximum absorption peak of ThIDTSe4F presented an obviously red-shift to 574 nm and enhanced molar extinction coefficient due to electronic-rich nature of selenophene, which is beneficial to harvest solar energy. From solution to the thin films, both of the two small-molecules exhibited obvious red-shifted absorption resulting from aggregation. Moreover, the prominent aggregation of 0-0 vibrational transition peaks marked the propensity of small molecule to aggregate in the solid state. These results was contributed from the F-S/Se or F-H interactions, which led to increase of molecular rigidity and planarity.53-57 Compared with its λmax in solutions, ThIDTTh4F red-shifted ca.58 nm at 0-0 vibrational transition peak in the thin films. Thin film of ThIDTSe4F displayed similar red-shift of λmax with slight higher 0-0/0-1 oscillator strength ratio of two transition peaks in comparison with that of ThIDTTh4F. Optical bandgaps (Eg(opt)) could be calculated by the onsets of thin-film absorption as 1.82 eV for ThIDTTh4F and 1.78 eV for ThIDTSe4F, respectively.

0.3 ThIDTTh4F ThIDTSe4F Absorbance Intensity

0.25

1

film

solution

0.8

0.2 0.6 0.15 0.4 0.1 ThIDTTh4F ThIDTSe4F

0.05 0 400

0.2

0 500

600 700 Wavelength (nm)

800


Normalized Absorbance Intensity

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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Figure 1: Absorption spectra of ThIDTTh4F and ThIDTSe4F in chloroform solutions (1×10-6 M) (on the left side) and in thin films (on the red side). To estimate the energy levels of ThIDTTh4F and ThIDTSe4F, cyclic voltammetry (CV) experiments based on the thin films of ThIDTTh4F and ThIDTSe4F were carried out. The HOMO and LUMO energy levels were calculated from the onset of oxidation potential and reduction potential, respectively. HOMO energy levels for ThIDTTh4F and ThIDTSe4F are 5.43 eV and -5.41 eV. The corresponding LUMO energy levels are -3.65 eV and -3.67 eV, respectively. Moreover, the electrochemical band gaps (Eg(cv)) were expectedly comparable to the corresponding Eg(opt). The details of the electrochemical properties are summarized in Table 1 and Figure S3. Compared to ThIDTTh4F, ThIDTSe4F showed smaller electrochemical band gaps and higher HOMO energy levels, which is expected to gain the higher Jsc and lower Voc of the organic

solar


cells.

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Table 1. Photophysical and electrochemical properties of ThIDTTh4F and ThIDTSe4F in solutions and in the thin films Compd

a

Eox(onset)

Ered(onset)

EHOMO

ELUMO

Eg(cv)

Eg(opt)

(film) (nm)

(V) a

(V) a

(eV)

(eV)

(eV)

(eV)

434, 554

452,570, 612

0.63

-1.15

-5.43

-3.65

1.78

1.82

446, 574

458,589, 631

0.61

-1.13

-5.41

-3.67

1.74

1.78

λmaxabs.

λmaxabs

(sol)(nm) ThIDTTh4F ThIDTSe4F

potentials are calculated relative to a Fc/Fc+ redox couple. Bulk heterojunction solar cells based on thin films of ThIDTTh4F and ThIDTSe4F

were

fabricated

using

the

device

structure

of

ITO/PEDOT:PSS/small-

molecule:PC71BM/PFN/Al (device area: 0.16 cm2) and tested under simulated AM 1.5G sun illumination. These active layer within the range of 80-100 nm films were obtained by spin-coating the optimized small molecules: PC71BM blend ratios (1:3 for ThIDTTh4F and 1:2 for ThIDTSe4F) in chlorobenzene solution. Figure 2 showed the JV curves of their best devices and Table 2 summarizes the parameters of optimized devices with and without post annealing treatments. As shown in Table 2, all of the ascasted devices based on ThIDTTh4F/PC71BM and ThIDTSe4F/PC71BM exhibited high Jsc and Voc, but modest fill factor (ca. 0.5), resulting in only modest PCEs. Surprisingly, ThIDTTh4F-based as-casted device displayed a higher PCE (4.91%) than these devices based on ThIDTSe4F (4.58%). Thermal annealing (TA) and solvent vapor annealing (SVA) were employed in controlling the morphology of small molecule and PC71BM blends, which in turn significantly improved organic solar cell efficiencies.58-63 We tired chloroform, THF, CH2Cl2 as the SVA solvents, but found that, contrary to most reports, the poor solvent CH2Cl2 led to the highest enhancement in PCE. Upon CH2Cl2 vapor treatment on the blend of ThIDTSe4F and PC71BM for 30 s, the device FF increased


9


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dramatically from 0.45 to 0.70 (over 50% enhancement), indicating that optimized morphological results were obtained in the blend films. Therefore, the blend of ThIDTSe4F achieved a higher Jsc of 12.32 mA cm-2, a reduced Voc of 0.83 V, and an overall PCE of up to 7.14%. The drop of Voc value after SVA treatment is consistent to that of our and other group’s report, which is likely as these results of morphological changes at the contact interfaces and reduction in the quasi Femi level gaps.61-63 Similarly, SVA-treated ThIDTTh4F/PC71BM blend films afford PCEs of 6.87% with increased Jsc (11.25 mA cm-2) and FF (0.68), and decreased Voc (0.90 V) in comparison with those of obtained as-cast blend films. Moreover, we further improved the PCE by TA and then SVA treatment. The active blend layers containing ThIDTSe4F/PC71BM reacted positively to TA + SVA treatment by slightly enhancing Jsc and resulting in an improved PCE to 7.31% with a high Jsc of 12.78 mAcm-2, a Voc of 0.83 V, and a high FF of 0.69. Moreover, the average PCE of 7.16% over than ten individual devices for the blend of ThIDTSe4F/PC71BM was achieved. The PCE of 7.31% with the high FF represent some of the best performances for OSCs achieved with organic small molecular donor designed on D-A-D-A-D sequence. Furthermore, such high efficiency is the highest value with small molecular donor materials based on aromatic side-chains functionalized IDT core.41-44 However, TA+SVA treatment did not lead to further PCE improvements in blend of ThIDTTh4F/PC71BM. In fact, the significant drop in Jsc from 11.25 to 10.63 mAcm-2 and FF from 0.68 to 0.59 with TA+SVA treatment implies that ThIDTTh4F may not be suitable for TA+SVA treatment. Overall, the PCE of ThIDTTh4F-based devices with TA+SVA treatment drops to a modest 5.73%. The slightly higher Voc (0.90 V) obtained from optimized ThIDTTh4F-based devices (0.83 V for ThIDTSe4F) is


10

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consistent to its slightly lower-lying HOMO energy levels in comparison with that of ThIDTSe4F. The most striking evidence that the π-bridge in ThIDT-based small molecular donor critically impacts materials performances.

0

7 ThIDTSe4F-As-cast ThIDTSe4F-SVA ThIDTSe4F-TA+SVA

-2

-2

ThIDTTh4F-As cast ThIDTTh4F-SVA ThIDTTh4F-TA+SVA -4

-8

PCE (%)

Current Density (mA cm )

0 Current Density (mA cm )

(c)

(b)

(a)

-4

6

-8

ThIDTTh4F ThIDTSe4F

5

-12

4 0

(d)

0.2

0.4 0.6 Voltage (V)

0.8

EQE (%)

ThIDTTh4F ThIDTSe4F

As-cast

SVA

TA+SVA

0.6

0.8

As cast

50

50

40 30

0 300

ThIDTTh4F-As cast ThIDTTh4F-SVA ThIDTTh4F-TA+SVA

400


SVA

TA+SVA

(f)70 60

10

0.4

0.2 0.4 Voltage (V)

60

20

0.5

0

(e) 70

0.7

0.6

-0.2

1

EQE (%)

-12 -0.2

FF

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


40 30 20

ThIDTSe4F-As cast ThIDTSe4F-SVA ThIDTSe4F-TA+SVA

10

700

800

0 300

400


700

800

Figure 2: J-V curves (a-b), PCE change (c) and FF change (d) dependence on the device treatment conditions, and EQE plots (e-f) based on the best result of two small molecules and PC71BM before/after post annealing treatments. Figure 2 gave the changes of these device parameters (PCE and FF) with changing their π-bridge and with/without post annealing treatments. Interesting, the SVA treatment was the best treatment for the improvement of FF. Compared to the initial performance based on as-cast film, it was found that ThIDTTh4F-based devices with SVA treatment showed the largest enhancement of PCE and ThIDTSe4F-based devices with TA+SVA treatment showed the largest enhancement of PCE. The Jsc gave a similar changing trend


11


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to

the

corresponding

PCE

values.

Compared

to

these

Page 12 of 39

Jscs

obtained

with

ThIDTTh4F/PC71BM blends, the obviously higher Jsc values obtained by post-treated ThIDTSe4F/PC71BM blends translated into higher EQE value cross the range of 400-700 nm (Figure 2). In particular, The EQE values (the maximum value of 66% at 560 nm) of TA+SVA treated ThIDTSe4F-based device (7.31% PCE) is higher than those achieved with ThIDTTh4F by ca. 10% across the range of 350-700 nm. Importantly, the decisive role of SVA or TA+SVA treatments in two small molecules-based devices is also apparent from the EQE curves. The EQE responses of as-cast ThIDTTh4F-based device remain under 55% across the range of 350-700 nm, which is consistent with the low Jsc value of ca. 10 mAcm-2. The notable increases in EQE with SVA or TA+SVA treatments indicated that favorable morphological changes were obtained as the solvent vapor diffuse into the blends to accelerate self-assembly of both donor molecules and PCBM. Absorption spectra of thin films of donor molecules and PCBM were first investigated to see the origin change of Jsc (see Figure S4). Both of SVA treated samples showed higher intensity in absorption spectra in comparison with these of as-cast thin films. Moreover, upon TA+SVA treatment, the blends of ThIDTSe4F/PC71BM exhibited further increase of absorption intensity with a relative obvious vibronic shoulder at region of 600-700 nm, which is consistent with the highest of Jsc upon TA+SVA treatment of the blend of ThIDTSe4F/PC71BM. It is indicated that when the solvent molecules get into the films, the local small molecular donor would became reorganize and/or improve the nanostructural order, which will be further analysed below. Table 2. A summary of the device performances from ThIDTTh4F/PC71BM and ThIDTSe4F/PC71BM.


12

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Jsc

Voc

Active layer (mA/cm2) ThIDTTh4F

PCE(best) FF

(V)

(%)

10.04±0.01 0.95±0.01 0.48±0.03 4.56±0.35（4.91）

ThIDTTh4Fa 11.24±0.28 0.89±0.01 0.65±0.02 6.51±0.26（6.87） ThIDTTh4Fb 11.17±0.96 0.85±0.02 0.58±0.02 5.45±0.32（5.73）

a

ThIDTSe4F

10.22±0.76 0.94±0.01 0.44±0.00 4.24±0.29（4.58）

ThIDTSe4Fa

12.46±0.10 0.83±0.00 0.68±0.01 7.05±0.06（7.14）

ThIDTSe4Fb

12.62±0.27 0.82±0.02 0.69±0.01 7.16±0.12（7.31）

with CH2Cl2 vapor annealing; bwith thermal annealing and followed with CH2Cl2 vapor

annealing.

Figure 3.

TEM images of thin films from ThIDTTh4F/PC71BM (a-c) or ThIDTSe4F

/PC71BM (d-f) before/after post annealing treatments. The white scale bar in images is 200 nm.


13


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Differences of thin film morphology of the active layers have a strong impact on organic solar cells efficiency. We first investigated the device morphologies of as-cast, SVA treated, and TA+SVA treated blend films by high-resolution TEM images. Both of as-cast films exhibited homogeneous with poor phase-separated feature (Figure 3). When these films were exposed to CH2Cl2 vapor, nanostructure and better phase separation was clearly found. Such morphology was beneficial to improving Jsc and FF for these two blend films. In TA+SVA treatments, ThIDTSe4F/PC71BM blends showed a sharper phase contrast (with a ca. 25 nm domain size) and enhanced fibrous structures comparing to single SVA treatment. Improved morphology allowed excitons to diffuse to the D/A interfaces and undergo charge transfer more efficiently, which gave rise to a further increase of Jsc. In contrast, ThIDTTh4F/PC71BM blends under this condition showed reduced phase contrast and thus the phase separation was smeared comparing to SVA processing. Thus efficiency of excitons splitting during D-A interfaces and hole/electron mobilities were low, which led to decrease of FF and Jsc.


14

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Figure

4.

GIXD patterns

of

(a)ThIDTSe4F/PC71BM

blend

films and

(c)

ThIDTTh4F/PC71BM blend films before/after post annealing treatments; In-plane and out of plane

and

line-cut

profiles

for

(b)

ThIDTSe4F/PC71BM


blend

films

and

(d)

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Page 16 of 39

ThIDTTh4F/PC71BM blend films before and after SVA or TA+SVA treatments. A stand for Angstroms.

We used grazing incidence X-ray diffraction (GIXD) to study the self-assembly in BHJ blends under different post annealing conditions (SVA or TA +SVA treatments). ThIDTSe4F/PC71BM blends showed quite different crystalline nature in differently processed BHJ blends. The as cast sample showed strong PCBM diffraction singles from PCBM (1.34 A-1) but no obvious donor molecule crystallization. SVA led to ThIDTSe4F crystallization, with (100) diffraction at 0.27 A-1 in in-plane direction and pi-pi stacking diffraction at 1.81 A-1 in out-of-plane direction. The crystal coherence length (CCL) for (100) peak is 13.74 nm and pi-pi stacking peak CCL is 1.97 nm. TA+SVA processing led to a similar crystalline feature in ThIDTSe4F/PC71BM blends, yet the CCL for (100) and pi-pi stacking peak slightly reduced. The peak area ration of pi-pi stacking/PCBM also showed reduction in TA+SVA sample comparing to single SVA sample, and thus crystalline order for ThIDTSe4F in TA+SVA processing is slightly reduced. Thus SVA or TA+SVA is more effective in driving the self-assembly of ThIDTSe4F molecules, leading

to

enhanced

hole/electron

mobilities

and

charge

collections.

For

ThIDTTh4F/PC71BM blends, as-cast thin film exhibited quite weak (100) and (010) diffraction intensity in comparison with that of ThIDTSe4F/PC71BM blends. These signals got enhanced under SVA processing. The (100) diffraction of in-plane direction located at 0.27 Å-1, which indicated that the alkyl-to-alkyl spacing distance is 2.33 nm. In addition, the π-π stacking peak is weak and merged with PCBM diffractions and thus could not be equivocally assessed. TA+SVA treatment gave similar results as in SVA


16

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treated BHJ thin film. It should be noted that ThIDTSe4F/PC71BM blends showed a stronger in-plane (100) peak and a stronger out-of-place (010) peak comparing to ThIDTTh4F/PC71BM blends in optimized conditions. It is suspected that π-bridges from thiophene to selenophene led to enhanced face-on packing and ordered structure due to the large sized selenium atoms and better planarity of whole molecules.64-65 Such results provide better charge transport pathways, thus improved PCE and FF in SVA or TA+SVA treated ThIDTSe4F/PC71BM-based BHJ thin films can be realized.

Figure 5. Resonant soft X-ray scattering profiles of (a) ThIDTSe4F/PC71BM blend films and (b) ThIDTTh4F/PC71BM blend films before and after annealing treatments. The phase separation in BHJ blends was investigated by RSoXS. Scattering curves of BHJ thin films based on two small molecules before and after annealing treatments are shown in Figure 5. The as-cast thin film for both ThIDTTh4F/PC71BM and ThIDTSe4F/PC71BM are quite well mixed as no obvious scattering peak can be observed. Thus in solar cell devices, both samples gave low performances, especially in device fill factor. SVA treatment led to


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Page 18 of 39

pronounced phase separation. In ThIDTSe4F /PC71BM case, a sharp scattering peak is seen at 0.010 A-1, which indicated the phase separation distance is about 63 nm. A high intensity in scattering peak indicated a sharp phase separation, and thus efficient exciton splitting and charge transport were achieved. Scattering peak of TA+SVA treated ThIDTTh4F/PC71BM blends was slightly shifted to 0.017 Å-1, which indicated the phase separation distance is about 37 nm. Thermal annealing before SVA process has led to decrease the distance of phase separation, which the exciton separation and charge transport should be more facile in BHJ blends. Improved Jsc was thus obtained. Although scattering intensity dropped, a good fill factor remained, leading to best PCE for TA+SVA solar cells. ThIDTTh4F/PC71BM sample SVA treatment showed a scattering peak at 0.033 Å-1, corresponding to a distance of 19 nm. Further TA+SVA treatment led to enhanced scattering peak intensity and slightly increased distances of phase separation (0.029 A-1, 21 nm). However, the correlated device performances dropped, especially the fill factor. It should be noted that the RSoXS intensity for ThIDTTh4F /PC71BM is much lower in post-treated BHJ thin films, and the fill factor of these devices is thus inferior. TA+SVA processed solar cells showed large reduction in fill factor, yet a sharper phase separation is observed, thus this reduction should be ascribed to a different mechanism (it will be discussed below).These information together with GIXD results demonstrate that suitable donoracceptor phase separation is important for highly efficient device. Moreover, SVA or TA+SVA processing promote the blend films to enhance crystalline nature and

improve phase separation.

Such results are similar to our and other group’ s report on understanding of SVA or TA+SVA in tuning the morphology of BHJ blends.61-63 The significant difference in morphology and device performance of these two molecules must be attributed to the change of π-bridge (thiophene and selenophene).


18

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As the improved crystalline content of the blend films may lead to the improvement in charge transport ability, therefore we measured the charge mobilities of ThIDTTh4F and ThIDTSe4F in as-cast, SVA treated, TA+SVA treated thin film, which were calculated by the space charge limited current (SCLC) method. Figure S5-S6 showed the dark current J-V curves of the blend films in hole-only devices (ITO/PEDOT/small molecules:PC71BM/MoO3/Al)

and

electron-only

devices

(ITO/ZnO/PFN/small

molecules:PC71BM/Ca/Al), and estimated hole/electron mobilities are provided in Table 3. The as-cast ThIDTSe4F/PC71BM films showed substantially higher hole mobility (3.8×10-5 cm2V-1s-1) than that for as-cast ThIDTTh4F/PC71BM films, which can be assigned to the chemical nature differences in two molecules due to selenium atom integration, which can provide pathways for holes to hope through molecules.

In

addition, SCLC results showed that hole mobilities have been increased upon SVA treatments and TA+SVA treatments for both two small molecules, with particularly notable increases (by 30-40 times) in thin film made with ThIDTTh4F/PC71BM, due to the drastic crystallinity change upon SVA treatment.. Moreover, the blend of ThIDTSe4F/PC71BM with the TA+SVA treatment exhibited a higher hole mobilities (7.7×10-4 cm2V-1s-1) than those using single SVA treatment, which consistent with the increase of PCE with TA+SVA treatment. And when conjugated with RSoXS and GIXD measurement, TA+SVA treatment provided further phase purification that generated better

transporting

pathways.

Meanwhile,

the

electron

mobility

(µe)

of

ThIDTSe4F/PC71BM blend film was slight increased to 8.1×10-4 cm2V-1s-1 after TA + SVA treatment, while the best electron mobility of ThIDTTh4F/PC71BM blend film was found when the film was treated with SVA treatment. Both blends with post-annealing


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Page 20 of 39

treatments exhibited high carrier mobilities in the 10-4 cm2V-1s-1regime, reflecting these notable improved device and morphology results as discussed above.

Moreover, the

charge carrier ratios between electron and hole are close to unity for those devices based on ThIDTSe4F/PC71BM with SVA or TA+SVA treatment, which led to their high Jsc and FFs (ca. 0.7).66-69 In turn, we found that the imbalance

charge mobilities in

ThIDTTh4F/PC71BM thin films with SVA or TA+SVA treatment is likely to be at the results of limiting the FFs and Jsc. Combined TEM, GIXD, RSoXS and SCLC analyses indicated the effect of SVA or TA+SVA treatment on morphologies and device performance is not independent of the π-bridges of the molecular structure of small molecular donor in organic solar cells.

Table

3.

A summary of the hole/electron mobilities from the blend films of

ThIDTTh4F/PC71BM and the blend films of ThIDTSe4F/PC71BM. µe

µh

µe/µh

Active layer (cm2V-1s-1) (cm2V-1s-1) ThIDTTh4F/PC71BM

8.7×10-4

7.6×10-6

114

ThIDTTh4F/PC71BM a

1.2×10-3

3.1×10-4

3.9

ThIDTTh4F/PC71BMb

9.8×10-4

2.1×10-4

4.7

ThIDTSe4F/PC71BM

3.8×10-4

3.8×10-5

10

ThIDTSe4F/PC71BM a

4.7×10-4

6.7×10-4

0.7

ThIDTSe4F/PC71BMb

8.1×10-4

7.7×10-4

1.1

a

with SVA; b with TA+SVA


20

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We also investigated the long term device stability in air after simple encapsulation. Most of devices in different post annealing treatment kept above 85% of original PCE after exposing them in air over 150 h (Figure S7 and S8). For example, for ThIDTSe4F/PC71BM devices after CH2Cl2 vapor annealing, the device retain its ~87% of the original PCE even after 150 h of exposing them in air. We believed that better device stability could be realized after we used better device architecture and better encapsulated condition.

CONCLUSIONS In summary, we synthesized a pair of two tetrafluorinated small molecular donors (ThIDTTh4F and ThIDTSe4F) and studied their potential application in organic solar cells. Two small molecules have same tetrathienyl side chain functionalized IDT (ThIDT) as electron-rich central core, electron-deficient difluorobenzothiadiazole as acceptor units, and donor end-capping groups, but having difference in the π-bridge (thiophene and selenophene), respectively. Our combined TEM, GIXD, RSoXS, and SCLC analyses indicated that using the tetrathienyl side chain functionalized IDT and changing the π-bridge impact the propensity of the small molecular donor to reorganization and increase of crystalline content when they are subjected to rapid SVA or TA+SVA treatment. Compared to ThIDTTh4F-based device, the more favorable carrier transport properties (high and balanced carrier mobilities) of active layer contribute to the higher PCE of 7.31% in the ThIDTSe4F based devices, which represented some of the best performances for OSCs achieved with organic small molecular donor designed on D-A-D-A-D sequence. Furthermore, such high efficiency is the highest value with small molecular donor materials based on aromatic side-chains functionalized IDT core. These results demonstrated that tetrathienyl side chain


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Page 22 of 39

functionalized IDT was an effective central cores for the design of novel highly efficient small molecules applied in organic solar cells. Our results indicated that the π-bridge of small molecular donor is one of the key factor for the effect of SVA or TA+SVA treatment on device performances. Further optimization of the chemical structure on this system is currently in progress to obtain better photovoltaic performance.

EXPERIMENTAL SECTION Materials and Characterization: All air sensitive reactions were carried out under N2. Toluene and THF was dried by Na and then freshly distilled before to use. The other precursors were used as the common commercial level. 1H and

13

C NMR spectra were

carried out on a Bruker Ascend-400 NMR spectrometer. All chemical shifts were reported in ppm. Chemical shifts in 1H NMR were referenced to TMS and in

13

C NMR were

referenced to CDCl3. Absorption spectra were carried out on Hitachi UH5300 UV-vis spectrometer. Cyclic voltammetry was recorded on CHI workstation. High-resolution TEM test was performed JEOL 2100F. Grazing incidence X-ray scattering (GIXD) and resonant soft X-ray scattering (RSoXS) were carried out at beamline 7.3.3 and 11.0.1.2 at Lawrence Berkeley National Lab.

3: To a solution of 2-ethylhexylthiophene (1.6 g, 8.0 mmol) in dry THF (10 mL) in N2 atmosphere under −78 °C was added n-BuLi (2.5 mL, 6.0 mmol), the mixture was kept at −78 °C for 1 h, and a solution of 1 (0.50 g, 1.0 mmol) in THF (20 mL) was then added slowly. The solution was stirred at room temperature for overnight, and then water was added in the solution. The organic phase was extracted with dichloromethane and washed with NaCl (aq.) and dried over Na2SO4. After removal of the solvent, the crude product


22

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was obtained as yellow oil after removing the solvents. The crude diol was then directly dissolved in HOAc (20 mL) and concentrated HCl (2 mL) was added to the solution. The solution was stirred at 80 oC for 12 h. And then water was added in the solution. The organic phase was extracted with dichloromethane and washed with NaCl (aq.) and dried over Na2SO4. The resulting crude product was purified by flash column chromatography (silica gel), eluting with petroleum ether to give colorless oil (0.32 g, 31%). 1H NMR (CDCl3, 400 MHz, ppm): δ 7.68 (s, 2H, Ph-H), 7.30-7.32 (d, J = 4.8 Hz, 2H, Th-H), 7.217.22 (d, J = 4.8 Hz, 2H, Th-H), 6.74-6.75 (d, J = 3.6 Hz, 4H, Th-H), 6.52-6.53 (d, J = 3.6 Hz, 4H, Th-H), 2.66-2.67 (d, J = 6.8 Hz, 8H, CH2), 1.52-1.55 (m, 4H, CH), 1.26-1.32 (m, 32H, CH2), 0.87-0.88 (m, 24H, CH3).

13

C NMR (CDCl3, 100 MHz, ppm): δ 155.1, 153.6,

145.3, 144.4, 141.6, 134.5, 127.6, 125.3, 124.2, 123.3, 117.3, 56.9, 41.4, 34.5, 32.5, 29.0, 25.8, 23.2, 14.3, 11.0. ESI-MS (m/z)

calcd for C64H82S6: 1042.4741 (M+), Found:

1043.4829 ([M+H+]+). 4: To a solution of 2 (0.20 g, 0.192 mmol) in THF (20 mL) and DMF (10 mL) was added N-bromosuccinimide (0.075 g, 0.42 mmol). The resulting solution was stirred at room temperature for 2 h. And then water was added in the solution. The organic phase was extracted with dichloromethane and washed with NaCl (aq.) and dried over Na2SO4. The resulting crude product was purified by flash column chromatography (silica gel), eluting with petroleum ether to give colorless oil (0.21 g, 91%). 1H NMR (CDCl3, 400 MHz, ppm): δ 7.56 (s, 2H, Ph-H), 7.20 (s, 2H, Th-H), 6.69-6.70 (d, J = 3.6 Hz, 4H, Th-H), 6.526.53 (d, J = 3.6 Hz, 4H, Th-H), 2.65-2.66 (d, J = 6.8 Hz, 8H, CH2), 1.51-1.53 (m, 4H, CH), 1.25-1.31 (m, 32H, CH2), 0.84-0.88 (m, 24H, CH3).

13

C NMR (CDCl3, 100 MHz,

ppm): δ 154.0, 152.7, 144.80, 144.77, 144.4, 141.6, 134.4, 126.2, 125.4, 124.3, 117.1,


23


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114.0, 57.6, 41.4, 34.5, 32.5, 29.0, 25.8, 23.8, 14.3, 11.0. ESI-MS (m/z)

Page 24 of 39

calcd for

C64H80Br2S6: 1198.2951 (M+), Found: 1199.3062 ([M+H+]+). ThIDTTh4F: In a 150 mL two-neck round-bottomed flask, dibromide 4 (0.18 g, 0.15 mmol), monotin reagent 5 (0.25 g, 0.38 mmol), Pd2(dba)3 (6.8 mg, 0.0075 mmol), tri(otolyl)3 (9.8 mg, 0.030 mmol) were added. The flask was evacuated and backfilled with N2 in three times, and then freshly distilled toluene (50 mL) was added into the mixture. The resulting solution was refluxed for 12 h. After removal of solvents, the dark residue was purified by flash column chromatography (silica gel), eluting with petroleum etherCH2Cl2 (10:1) to give dark solid (0.22 g, 74%). 1H NMR (CDCl3, 400 MHz, ppm): δ 8.20-8.22 (d, d, J = 3.6 Hz, 4H, Th-H), 7.66 (s, 2H, Ph-H), 7.45 (s, 2H, Th-H), 7.34-7.35 (d, J = 4.0 Hz, 2H, Th-H), 7.23-7.24 (d, J = 4.0 Hz, 2H, Th-H), 7.14-7.15 (d, J = 3.6 Hz, 2H, Th-H), 6.79-6.80 (d, J = 3.6 Hz, 4H, Th-H), 6.73-6.74 (d, J = 3.6 Hz, 2H, Th-H), 6.55-6.56 (d, J = 3.6 Hz, 4H, Th-H), 2.80-2.84 (t, J = 7.6 Hz, 4H, CH2), 2.67-2.69 (d, J = 6.8 Hz, 8H, CH2), 1.69-1.73 (m, 4H, CH), 1.56 (m, 4H, CH), 1.27-1.41 (m, 44H, CH2), 0.85-0.89 (m, 30H, CH3).

13

C NMR (CDCl3, 100 MHz, ppm): δ 156.0, 153.6, (151.3,

151.1, 148.8,148.5, JCF = 257, 20 Hz), (148.9,148.8, JCF = 10 Hz), (151.1, 150.9, 148.5,148.3, JCF = 259, 20 Hz), 146.7, (144.75, 144.73), (141.69, 141.61, 141.59, 141.52, JCF = 10 Hz), 141.2, 139.7, 134.6, 134.4, (132.0, 131.9), 130.7, 130.0, 125.5, 125.3, 124.3, 123.8, 123.3, 120.3, 117.2, (111.6, 111.5, JCF = 12 Hz), (111.2, 111.1, JCF = 12 Hz), 57.3, 41.4, 34.6, 32.6, 31.8, 31.7, 30.4, 29.0, 25.8, 23.2, 22.8, 14.4, 14.3, 11.0. MALDI-TOF MS (m/z) calcd for C112H118F4N4S14: 2042.5 (M+), Found: 2042.6 (M+). 7: In a 100 mL round-bottomed flask, 6 (0.50 g, 1.0 mmol), 2-tributyltinselenophene (0.63 g, 1.5 mmol), Pd2(dba)3 (45 mg, 0.05 mmol), tri(o-tolyl)3 (63 mg, 0.2 mmol) were


24

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added. The flask was evacuated and backfilled with N2 in three times, and then freshly distilled (50 mL) was added into the mixture. The resulting solution was refluxed for 12 h. After removal of the solvents, the dark residue was purified by flash column chromatography (silica gel), eluting with petroleum ether-CH2Cl2 (30:1) to give red solid (0.50 g, 91%). 1H NMR (CDCl3, 400 MHz, ppm): δ 8.49-8.50 (d, J = 3.6 Hz, 1H, Se-H), 8.34-8.35 (d, J = 5.6 Hz, 1H, Se-H), 8.20-8.21 (d, J = 3.6 Hz, 1H, Th-H), 7.50-7.53 (m, 1H, Se-H), 7.23-7.24 (d, J = 3.6 Hz, 1H, Th-H), 7.15-7.16 (d, J = 3.6 Hz, 1H, Th-H), 6.73-6.74 (d, J = 3.6 Hz, 1H, Th-H), 2.80-2.84 (t, J = 7.2 Hz, 2H, CH2), 1.69-1.72 (m, 2H, CH2), 1.32-1.42 (m, 6H, CH2), 0.89-0.92 (m, 3H, CH3).

13

C NMR (CDCl3, 100 MHz,

ppm): δ (151.2, 151.0, 148.6, 148.4, JCF = 258, 20 Hz), (151.0, 150.8, 148.5, 148.3, JCF = 258, 20 Hz), (149.1, 149.0, JCF = 9 Hz), (148.7, 148.6, JCF = 9 Hz), 146.7, 136.1, (135.4, 135.3, JCF = 7 Hz), 134.4, (133.1, 132.9, JCF = 7 Hz), 132.0, 130.3, 129.9, 125.2, 124.3, 123.3, (113.3, 113.2, JCF = 12 Hz), (111.6, 111.5, JCF = 12 Hz), 31.8, 31.7, 30.5, 29.0, 22.8, 14.3. ESI-MS (m/z) calcd for C24H20F2N2S3Se: 549.9916. Found: 549.9915 (M+). 8: To a solution of 7 (0.50 g, 0.91 mmol) in dry THF (50 mL) was added a solution of lithium diisopropylamide in THF (10 mL, 1.5 mmol) dropwise in N2 atmosphere at -78 °C. The mixture was stirred at −78 °C for 1 h and Me3SnCl (0.32 g, 1.6 mmol) in dry THF (10 mL) was added. The solution was stirred at room temperature for 10 h, and then water was added in the solution. The organic phase was extracted with dichloromethane and washed with NaCl (aq.) and dried over Na2SO4. After removal of the solvent, the crude product was recrystallized (MeOH/CHCl3) to afford red solid (0.60 g, 90%). 1H NMR (CDCl3, 400 MHz, ppm): δ 8.53-8.54 (d, J = 3.6 Hz, 1H, Se-H), 8.20-8.21 (d, J = 3.6 Hz, 1H, Th-H), 7.68-7.69 (d, J = 3.6 Hz, 1H, Se-H), 7.23-7.24 (d, J = 3.6 Hz, 1H, Th-


25


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Page 26 of 39

H), 7.15-7.16 (d, J = 3.6 Hz, 1H, Th-H), 6.73-6.74 (d, J = 3.6 Hz, 1H, Th-H), 2.81-2.84 (t, J = 7.2 Hz, 2H, CH2), 1.69-1.73 (m, 2H, CH2), 1.32-1.41 (m, 6H, CH2), 0.91-0.92 (t, J = 6.8 Hz, 3H, CH3). 0.44 (s, 9H, Sn-CH3).

13

C NMR (CDCl3, 100 MHz, ppm): δ (151.3,

151.1, 148.6, 148.5, JCF = 259, 18 Hz), (151.5, 150.4, 148.0, 147.8, JCF = 259, 16 Hz), (149.3, 149.2, JCF = 9 Hz), (148.7, 148.6, JCF = 10 Hz), 146.7, (141.47, 141.53, JCF = 6 Hz), 138.4, 134.4, (133.8, 133.7, JCF = 11 Hz), (131.9, 131.8, JCF = 9 Hz), 130.3, 130.1, 125.2, 124.3, 123.4, (113.5, 113.4, JCF = 12 Hz), (111.5, 111.3, JCF = 12 Hz), 31.8, 31.7, 30.5, 29.0, 22.8, 14.3, -7.7. ESI-MS (m/z) calcd for C27H28F2N2S3SeSn: 713.9567. Found: 713.9577 (M+). ThIDTSe4F: In a 150 mL round-bottomed flask, dibromide 4 (0.14 g, 0.12 mmol), monotin reagent 8 (0.21 g, 0.30 mmol), Pd2(dba)3 (5.5 mg, 0.0075 mmol), and tri(otolyl)3 (7.6 mg, 0.024 mmol) were added. The flask was evacuated and backfilled with in N2 three times, and then freshly distilled toluene (60 mL) was added into the mixture. The resulting solution was refluxed for 12 h. After removal of solvents, the dark residue was purified by flash column chromatography (silica gel), eluting with petroleum etherCH2Cl2 (8:1) to give desired target materials (0.20 g, 78%). 1H NMR (CDCl3, 400 MHz, ppm): δ 8.36-8.37 (d, J = 4.4 Hz, 2H, Se-H), 8.20-8.21 (d, J = 4.0 Hz, 2H, Th-H), 7.66 (s, 2H, Ph-H), 7.49-7.50 (d, J = 4.4 Hz, 2H, Se-H), 7.39 (s, 2H, Th-H), 7.22-7.23 (d, J = 3.6 Hz, 2H, Th-H), 7.14-7.15 (d, J = 3.6 Hz, 2H, Th-H), 6.78-6.79 (d, J = 3.6 Hz, 4H, Th-H), 6.73-6.74 (d, J = 3.6 Hz, 2H, Th-H), 6.55-6.56 (d, J = 3.6 Hz, 4H, Th-H), 2.80-2.84 (t, J = 7.6 Hz, 4H, CH2), 2.67-2.69 (d, J = 6.8 Hz, 8H, CH2), 1.69-1.73 (m, 4H, CH), 1.55 (m, 4H, CH), 1.27-1.41 (m, 44H, CH2), 0.85-0.89 (m, 30H, CH3).

13

C NMR (CDCl3, 100

MHz, ppm): δ 153.6, (151.2, 151.0, 148.5,148.3, JCF = 270, 20 Hz), (149.1,149.0, JCF = 6


26

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Hz), 148.6, (151.1, 151.9, 148.4,148.2, JCF = 268, 20 Hz), 147.5, 146.8, 144.8, 142.2, 141.7, 141.4, 134.6, 134.4, 134.0, (132.04, 131.99, JCF = 5 Hz), 130.0, 126.1, 125.5, 125.3, 124.3, 123.4, 120.8, 117.3, (113.11, 113.04, 112.98, JCF = 7 Hz), (111.4, 111.3, JCF = 11 Hz), 57.3, 41.4, 34.6, 32.6, 31.8, 31.7, 30.5, 29.0, 25.9, 23.2, 22.8, 14.4, 11.0. MALDI-TOF MS (m/z) calcd for C112H118F4N4S12Se2: 2138.4 (M+), Found: 2138.6 (M+).

ASSOCIATED CONTENT Supporting Information. The supporting information is available free of charge on the ACS Publications website. The additional experimental results (TGA curve, DSC curve, cyclic voltammetry curve, Absorption spectra of blends，J-V plots of the hole only or electron devices, stability curves of these devices) and the copies of 1H NMR and

13

C NMR are described in

Supporting Information.

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] (J. L. Wang) *E-mail: [email protected] (H.B. Wu) *E-mail: [email protected] (F. Liu) Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. §These authors contributed equally.


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Funding Sources This work was financially supported by the grants from the Natural Science Foundation of China (No. 21472012, 21672023, 91333206). J.-L. Wang was supported by the Thousand Youth Talents Plan of China and Beijing Natural Science Foundation (2152027). FL was supported by young 1000 talent program and TPR was supported by the U.S. Office of Naval Research under contract N00014-15-1-2244 and part of the experiments were conducted at ALS beamlines, which were supported by the DOE, Office of Science, and Office of Basic Energy Sciences. The authors thank Dr. Yazhong Dai and Prof. Jian Pei (Peking University) for DSC experiments.

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ToC figure


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Applying Thienyl Side Chains and Different Ï-Bridge to Aromatic Side

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