PushâPull Type Non-Fullerene Acceptors for Polymer Solar Cells

Subscriber access provided by University of South Florida

Article

Push-Pull Type Non-Fullerene Acceptors for Polymer Solar Cells: Effect of the Donor Core Zhenjing Kang, Shan-Ci Chen, Yunlong Ma, Jianbin Wang, and Qingdong Zheng ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b05417 • Publication Date (Web): 05 Jul 2017 Downloaded from http://pubs.acs.org on July 5, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Applied Materials & Interfaces is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 20

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

ACS Applied Materials & Interfaces

Push-Pull Type Non-Fullerene Acceptors for Polymer Solar Cells: Effect of the Donor Core Zhenjing Kang,†,‡ Shan-Ci Chen,† Yunlong Ma,†,‡ Jianbin Wang,†,‡,§ Qingdong Zheng†,* †

State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of

Matter, Chinese Academy of Sciences, 155 Yangqiao West Road, Fuzhou, Fujian 350002, China. ‡

University of Chinese Academy of Sciences, 19 Yuquan Road, Beijing 100049, China.

§

Department of Physics & Electronics Information Engineering, Minjiang University, Fuzhou,

Fujian 350108, China. KEYWORDS: polymer solar cell, non-fullerene acceptor, push-pull; indenothiophene; power conversion efficiency

ACS Paragon Plus Environment

1


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

Page 2 of 20

ABSTRACT: There has been a growing interest in the design and synthesis of non-fullerene acceptors for organic solar cells which may overcome the drawbacks of the traditional fullerenebased acceptors. Herein, two novel push-pull (acceptor-donor-acceptor) type small molecule acceptors, i. e. ITDI and CDTDI, with indenothiophene and cyclopentadithiophene as the core units and 2-(3-oxo-2,3-dihydroinden-1-ylidene)malononitrile (INCN) as the end-capping units are designed and synthesized for non-fullerene polymer solar cells (PSCs). After device optimization, PSCs based on ITDI exhibit good device performance with power conversion efficiency (PCE) as high as 8.00% outperforming the CDTDI-based counterparts fabricated under an identical condition (2.75% PCE). We further discuss the performance of these nonfullerene PSCs by correlating the energy level, carrier mobility with the core of non-fullerene acceptors. These results demonstrate that indenothiophene is a promising electron donating core for high performance non-fullerene small molecule acceptors.

1. INTRODUCTION In the past decades, polymer solar cells (PSCs) have attracted tremendous attention owing to their low-cost, good flexibility, light-weight and large-area processability.1-3 Typical PSCs are fabricated using a bulk heterojunction (BHJ) active layer which consists of a p-type semiconducting polymer as the donor material and an n-type semiconductor as the acceptor material.4-5 Not until two years ago, the fullerene derivatives (PC61BM, PC71BM, etc) had been predominant acceptors for PSCs because of their high mobility and isotropic electron-transfer properties.2, 6 Nevertheless, the fullerene derivatives have some intrinsic drawbacks such as small optical absorption coefficient and poor bandgap tunability,7 which restrict a further power conversion efficiency (PCE) increase for PSCs. Thus, non-fullerene semiconducting acceptors


2

Page 3 of 20

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


are emerging to address these drawbacks with their wide-range tunable energy levels, high absorption coefficients and easy synthetic accessibility.8-11 Among them, n-type small molecule acceptors with an acceptor-donor-acceptor (A-D-A) structure such as ITIC12 and IDTBR13 have been extensively explored in the recent years. Significant progresses have been made in this field, and PCEs over 12% have been achieved for PSCs based on the non-fullerene acceptors.14-16 Typically, push-pull (A-D-A) type small molecule acceptors feature with electron-donating cores end-capped

by

electron-withdrawing

ylidene)malononitrile12,

17-18

groups

such

as

(INCN) and 3-ethylrhodanine.13,

2-(3-oxo-2,3-dihydroinden-1-

19-20

It is worth noting that the

electron-donating cores of most A-D-A structured small molecule acceptors were based on symmetrical core units such as 4,9-dihydro-s-indaceno[1,2-b:5,6-b']dithiophene (IDT)21-23 and 6,12-dihydro-dithieno[2,3-d:2',3'-d']-s-indaceno[1,2-b:5,6-b']dithiophene

(IDTT).12,

24-25

Whereas, small molecule acceptors based on asymmetrical cores have been seldom reported. Recently, our group first developed the indenothiophene building block as the donor unit for efficient p-type D-A copolymers which exhibited an open circuit voltage (Voc) up to 1.0 V and a PCE over 9.0%.26-27 These results demonstrated that the indenothiophene is a promising electron donating unit towards high performance p-type semiconductors for PSCs. However, it is even more interesting to design n-type indenothiophene-based semiconductors by incorporating strong electron withdrawing units. In this context, we report on the design and synthesis of two small molecule acceptors, ITDI and CDTDI (shown in Figure 1), with indenothiophene and cyclopentadithiophene as the core units, respectively, and INCN as the end-capping units. The optical, electrochemical properties of the two small molecule acceptors were investigated. PSCs were fabricated by using poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5b′]dithiophene)-co-(1,3-di(5-thiophene-2-yl)-5,7-bis(2-ethylhexyl)benzo[1,2-c:4,5c′]dithiophene-


3


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

Page 4 of 20

4,8-dione)] (PBDB-T)15 as the hole transporting material. The best performance PSC based on ITDI exhibited a PCE of 8.00% outperforming the CDTDI-based counterpart (2.75% PCE) which demonstrates the good potential of indenothiophene for the construction of high performance non-fullerene acceptors. The results also demonstrate the significant effect of the donor core on the bandgap, carrier mobility as well as the photovoltaic properties of the resulting non-fullerene acceptors.

Figure 1. Chemical structures of ITDI, CDTDI and PBDB-T. 2. EXPERIMENTAL SECTION The synthetic details of ITDI and CDTDI are described in Supporting Information. Device Fabrication and Characterization PSCs were fabricated with the device structure of ITO/ZnO/active layer/MoO3/Ag. The ITO glass was cleaned by sequential ultrasonication in H2O containing detergent, deionized H2O, acetone, and isopropyl alcohol for 30 min each. Later, the ITO-glass was dried overnight in an oven. The ZnO precursor solution (0.23 M in 2-methoxyethanol, ethanolamine as a stabilizer) was spin-coated onto the UV-O3-pretreated (15 min) ITO-glass. When the obtained films were annealed at 130 °C for 10 min on a hot plate, they were then thermally annealed in an oven (200


4

Page 5 of 20

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


o

C) for one hour. The PBDB-T:ITDI blend (wt/wt, 1:1) was dissolved in chlorobenzene:diphenyl

ether (CB/DPE, v/v, 98/2) with a concentration of 18 mg/mL. After the blend solution was stirred at 50 °C for 6 hours, it was spin-coated inside the glovebox, followed by annealing at 120 °C for 10 min. Finally, 10 nm thick MoO3 film was deposited on the BHJ layer, and 100 nm of Ag layer was deposited to complete the top electrode fabrication. In this work, the active area of PSCs was fixed at 6 mm2. 3. RESULTS AND DISCUSSION Synthesis of ITDI and CDTDI

Scheme 1. Synthetic routes of ITDI and CDTDI. The synthetic routes of ITDI and CDTDI are shown in Scheme 1. IT-Sn was prepared according to one of our previous literatures.26 Compounds 3 and 6 were prepared in yields of 45% and 32%, respectively, by the palladium catalyzed Stille-coupling reaction. The target molecules ITDI and CDTDI were obtained in yields of 42% and 55%, respectively, by the Knoevenagel condensation with compound 4. The structures of both acceptors were determined by NMR and mass spectroscopy. Elemental analysis results indicate the high purity of the target


5


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

Page 6 of 20

acceptors. Both ITDI and CDTDI are highly soluble in common solvents such as chlorobenzene, chloroform, and dichloromethane at ambient temperature. Optical and Electrochemical Properties

Figure 2. (a) Absorption spectra of ITDI and CDTDI in chloroform solution. (b) Normalized absorption of neat films of ITDI and CDTDI. The linear absorption spectra of ITDI and CDTDI in solution and in solid film are depicted in Figure 2. As shown in Figure 2a, ITDI in chloroform solution exhibited a strong absorption band of 500-740 nm with a maximum extinction coefficient of 1.04×105 M-1 cm-1 at 647 nm. In comparison with ITDI, CDTDI showed a red-shifted absorption with a similar maximum


6

Page 7 of 20

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


extinction coefficient (1.05×105 M-1 cm-1 at 720 nm). Compared to the absorption in solution, the absorption of both ITDI and CDTDI in thin film exhibited a broader and red-shifted absorption, implying stronger intermolecular interaction for the ITDI and CDTDI molecules in solid state. According to the equation of Egopt= 1240/λonset (eV), the optical bandgap of ITDI calculated from thin film absorption onset is 1.53 eV, 0.17 eV larger than that of CDTDI (1.36 eV) (see Table 1). Furthermore, as can be seen from the blend film absorption (see Figure S2), both ITDI and CDTDI have well matched absorption spectra with polymer PBDB-T, especially for the absorption of PBDB-T:CDTDI which extends to the near-infrared region.

Figure 3. (a) Cyclic voltammogram of ITDI and CDTDI. (b) Estimated energy levels of PBDBT, CDTDI and ITDI from electrochemical cyclic voltammetry.


7


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

Page 8 of 20

Table 1. Optical and electrochemical properties of ITDI and CDTDI. Extinction Acceptors

coefficient (M-1 cm-1)

λonset (nm) in film

Egopt (eV)a

HOMO (eV)b

LUMO (eV)c

Egec (eV)d

-4.26

1.49

-4.18

1.71

CDTDI

1.05×105

913

1.36

-5.75

ITDI

1.04×105

813

1.53

-5.89

a

b

c

Estimated from the thin film absorption onset. EHOMO = -(φox+4.82) eV, ELUMO = -(φred+4.82) eV. d Egec = electrochemical bandgap.

The electrochemical properties of ITDI and CDTDI were studied by cyclic voltammetry (CV) using Pt as working electrode in 0.1 M Bu4NPF6 acetonitrile solutions at a scan rate of 100 mV/s. Ferrocene was used as a standard with a highest occupied molecular orbital (HOMO) energy level at -4.80 eV. Under the same condition, the onset oxidation potential (E1/2 ox) of ferrocene was measured to be -0.02 V versus Ag/Ag+. As shown in Table 1 and Figure 3a, the HOMO energy levels for CDTDI and ITDI were calculated to be -5.75 and -5.89 eV, respectively, according to the equation of EHOMO = -(φox+4.82) eV. While, the lowest unoccupied molecular orbital (LUMO) energy levels for CDTDI and ITDI were calculated to be -4.26 and -4.18 eV, respectively, according to the equation of ELUMO = -(φred+4.82) eV. The relatively high lying LUMO energy level of ITDI is favorable for obtaining a large Voc of the corresponding device. As shown in Figure 3b, the HOMO and LUMO energy levels of PBDB-T generally match with those of two small molecule acceptors, which is favorable for efficient exciton dissociation. In order to know whether there is efficient exciton dissociation as well as charge transfer between the acceptors and the polymer donor (PBDB-T), photoluminescence (PL) properties of the blend films were investigated. For comparison, the emission spectra of pure PBDB-T and the acceptors were also tested. The PL spectra of the blend films in comparison with those of pure donor or acceptor films are shown in Figure S1. It is found that the fluorescence emission of the


8

Page 9 of 20

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


donor polymer (PBDB-T) is completely quenched by the acceptor (ITDI, or CDTDI), suggesting efficient electron transfer from the polymer donor (PBDB-T) to the acceptor (ITDI, or CDTDI). Meanwhile, the emission of ITDI is also completely quenched by PBDB-T, which further confirms the efficient hole transfer from the ITDI acceptor to the PBDB-T donor. While in the case of CDTDI, the luminescence quenching is not so complete due to its elevated HOMO level. These results suggest that the exciton dissociation efficiency between PBDB-T and ITDI is higher than those between PBDB-T and CDTDI, which is in agreement with the larger photocurrent value for the PSC based on PBDB-T:ITDI.

Photovoltaic Properties Inverted PSC devices were fabricated to study the photovoltaic properties of the two acceptors. The current density–voltage (J–V) characteristics of the obtained PSCs are depicted in Figure 4a, and the corresponding photovoltaic parameters are summarized in Table 2. The device fabrication conditions were optimized by using ITDI as the electron transporting material. The as-cast PBDB-T:ITDI device exhibited the best PCE of 6.25% with a Voc of 0.93 V, a shortcircuit current density (Jsc) of 12.91 mA/cm2, and a fill factor (FF) of 51.78%. And then, the active layers were thermally annealed at different temperatures to optimize the device performance further (Table S1, Supporting Information). As shown in Table 2 and Table S1, increased Jsc and FF values were observed after thermal annealing at 120 °C for 10 min, and a higher PCE of 7.36% was obtained with a Voc of 0.92 V, a Jsc of 13.89 mA/cm2 and a FF of 57.66%. Later, the performance of PSCs was further optimized by tuning the solvent compositions through mixing chlorobenzene with a trace amount of 1,8-diiodooctane (DIO) or diphenyl ether (DPE). It seems that DIO has no impact on the enhancement of device


9


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

Page 10 of 20

performance (Table S2, Supporting Information). However, by adding 2% DPE to the active layer, a PCE of 8.00% was achieved for the best performance PBDB-T:ITDI-based device (Voc = 0.94 V, Jsc = 14.27 mA/cm2, FF = 59.72%). Under the same condition, the PSC based on PBDB-T:CDTDI exhibited a relatively low PCE of 2.75% with a Voc of 0.86 V, a Jsc of 8.38 mA/cm2 and a FF of 38.43%. The relatively low performance of PBDB-T:CDTDI-based device may due to the poor hole transfer between PBDB-T and CDTDI, which is correspondence with the aforementioned photoluminescence quenching experimental results. Further, these results show pronounced effects of the donor core on the photovoltaic performance of the small molecule acceptors. CDTDI differs from ITDI in that the symmetric cyclopentadithiophene core is replaced by the asymmetric indenothiophene (bridged by a thiophene), which has relatively weak electron donating ability and can endorse ITDI a deeper HOMO energy level in comparison with CDTDI. It should be noted that the energy levels of both electron-transporting (acceptor) and hole-transporting (donor) materials can influence the PSC performance not only by controlling the amount of light absorption through the BHJ layer, but also by affecting the charge transfer and exciton dissociation efficiencies of the BHJ layer. Table 2. Performance parameters of PSCs based on PBDB-T:acceptor. Active layera

Additive

Voc [V]

Jsc [mA/cm2]

FF [%]

PCE (best) [%]c

PBDB-T:ITDI

w/o

0.93 ± 0.00

12.98 ± 0.16

49.89 ± 1.99

6.04 ± 0.26 (6.25)

PBDB-T:ITDIb

w/o

0.93 ± 0.01

13.55 ± 0.37

58.04 ± 0.68

7.28 ± 0.08 (7.36)

PBDB-T:ITDIb

2% DPE

0.94 ± 0.00

13.94 ± 0.29

59.78 ± 0.56

7.82 ± 0.11 (8.00)

PBDB-T:CDTDI

w/o

0.87 ± 0.01

3.91 ± 0.41

26.77 ± 0.53

0.97 ± 0.09 (1.19)

PBDB-T:CDTDIb

w/o

0.88 ± 0.01

5.79 ± 0.46

30.56 ± 0.66

1.55 ± 0.15 (1.76)

PBDB-T:CDTDIb

2% DPE

0.86 ± 0.00

7.89 ± 0.27

37.36 ± 0.89

2.54 ± 0.13 (2.75)

a

The blend ratio was fixed at 1:1. b Annealing at 120 oC. obtained from 8 devices.

c

Average PCEs and standard deviations were


10

Page 11 of 20

(a) 2

Current density (mA/cm2)

(a)

0 ITDI CDTDI

-2 -4 -6 -8 -10 -12 -14 -16 -0.2

0.0

0.2

0.4

0.6

0.8

1.0

Voltage (V) 16

70 60

ITDI CDTDI

14 12

50

10 40 8 30 6 20

4

ITDI CDTDI

10 0 300

400

500

600 700 Wavelength (nm) Wavelength (nm)

2 800

Integrated JSC (mA/cm2)

(b)

EQE (%)

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


0 900

Figure 4. J-V curves (a) and EQE spectra (b) for PSCs based on PBDB-T:acceptor with 2% DPE. External quantum efficiencies (EQEs) of the best performance devices based on the two acceptors with DPE were investigated in order to prove the accuracy of the PCE measurement. The obtained EQE spectra were depicted in Figure 4b. The PSC based on PBDB-T:CDTDI showed a broader photoresponse range from 300 to 900 nm than that of PBDB-T:ITDI-based device in agreement with the corresponding absorption spectra of the blend films. The maximum EQE values of PBDB-T:ITDI and PBDB-T:CDTDI-based devices are 63.2% and 35.5%, respectively. The Jsc values of PBDB-T:ITDI and PBDB-T:CDTDI-based devices obtained by


11


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

Page 12 of 20

integrating the EQE spectra with the AM 1.5G reference spectrum are 13.68 mA cm−2 and 8.56 mA cm−2, respectively, which are in correspondence with the Jsc values obtained from the J−V measurements. AFM Morphologies and Charge Carrier Mobilities

Figure 5. AFM height (a-c) and phase (d-f) images of PBDB-T:ITDI films without annealing (a, d), with annealing (b, e), and with 2% DPE and annealing (c, f). Atomic force microscopy (AFM) was performed to investigate the surface morphology changes of the active layer induced by the thermal annealing and the DPE additive. The obtained AFM images are depicted in Figure 5a-f. From the AFM height images shown in the figure, one can observe similar mean-square surface roughnesses (RMS) of 2.12 and 2.11 nm for the as-cast film and the 120 oC annealed film, respectively. A widely distributed fibrillar nanostructure is


12

Page 13 of 20

observed for the both films. However, compared to that of the annealing-free film, the fibrillar nanostructure width of the thermally annealed film is much larger. Besides, the phase image of the active layer after the thermal treatment (Figure 5e) has clearer phase separation features in comparison to that of the film without annealing (Figure 5d). And the clearer phase separation features can be further enhanced after the addition of DPE (Figure 5f). The more obvious phase separation features and the improved crystalline properties caused by the treatments of the DPE additive and thermal annealing may lead to increased carrier transporting mobility as well as enhanced exciton dissociation efficiency for the corresponding devices. In order to verify the influence of different core units of small molecule acceptors on charge transport properties, space charge-limited current (SCLC) method was used to measure electron mobilities of ITDI and CDTDI (Figure 6). With the device structure of ITO/ZnO/active layer/Ca/Al for electron-only device, the ITDI-based devices demonstrated a relative higher electron mobility of 9.15×10-6 cm2 V-1 s-1 in comparison with the CDTDI-based devices (3.07×10-6 cm2 V-1 s-1). The higher charge mobility of ITDI is in correspondence with the larger current densities and FFs of the ITDI-based devices.

J0.5 (A0.5/m)

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


VAPPL-VBI (V)


13


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

Page 14 of 20

Figure 6. J0.5~V characteristics for ITDI-based and CDTDI-based electron-only devices. Solar Cell Stability For the practical application of PSCs, long-term device stability is vital in addition to the high efficiency. Therefore, we further examined the shelf-life stability of the non-fullerene PSCs. The device was encapsulated with epoxy and stored in air. The device stability of PBDB-T:ITDIbased PSC in ambient air is shown in Figure S3. In general, good shelf-life stability was observed for the encapsulated device based on PBDB-T:ITDI. The PCE of the device retained over 93% of its initial value after storage for 30 days. Specifically, during the period of 30 days, the FF and Voc values of the device were quite stable with nearly no attenuation. However, a slightly decreased Jsc was observed thereby leading to a small degradation in PCE of the device based on PBDB-T:ITDI.

4. CONCLUSION In summary, we designed and synthesized two small molecule acceptors, ITDI and CDTDI, with indenothiophene and cyclopentadithiophene as core units, respectively, and end-capping with INCN. ITDI possesses an optical bandgap of 1.53 eV which is larger than CDTDI (1.36 eV). After the optimization through solvent additive and thermal annealing, the best performance PBDB-T:ITDI-based device showed a PCE of 8.00% with a high Voc of 0.94 V. In contrast, the PBDB-T:CDTDI-based device fabricated under the identical condition showed a relatively low PCE of 2.75%. Thus, this work shows that the indenothiophene is a more promising electron donating core in comparison with the cyclopentadithiophene. Furthermore, this work provides another option for the construction of efficient non-fullerene small molecule acceptors by the incorporation of the asymmetrical indenothiophene.


14

Page 15 of 20

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


ASSOCIATED CONTENT Supporting Information The supporting information is available free of charge via the Internet at http://pubs.acs.org. Materials and instruments; synthetic details of ITDI and CDTDI; photoluminescence spectra of acceptors, polymer donor and polymer blends; absorption spectra of polymer blends; device stability of PSCs based on PBDB-T:ITDI; device performances of PSCs based on PBDBT:ITDI with different additives and annealing temperatures; and NMR and MS spectra of new compounds and intermediates (Figures S4-S13). AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] ACKNOWLEDGMENT Z. Kang and S.-C. Chen contributed equally to this work. This work was supported by the National Natural Science Foundation of China (Nos. U1605241, 61325026, 51561165011), the Key Research Program of Frontier Sciences, CAS (No. QYZDB-SSW-SLH032), the CAS/SAFEA International Partnership Program for Creative Research Teams, and the Strategic Priority Research Program of the Chinese Academy of Sciences, Grant No. XDB20000000. REFERENCES (1) Chen, J.-D.; Cui, C.; Li, Y.-Q.; Zhou, L.; Ou, Q.-D.; Li, C.; Li, Y.; Tang, J.-X., SingleJunction Polymer Solar Cells Exceeding 10% Power Conversion Efficiency. Adv. Mater. 2015, 27 (6), 1035-1041.


15


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

Page 16 of 20

(2) He, Z.; Xiao, B.; Liu, F.; Wu, H.; Yang, Y.; Xiao, S.; Wang, C.; Russell, T. P.; Cao, Y., Single-junction Polymer Solar Cells with High Efficiency and Photovoltage. Nat. Photonics 2015, 9 (3), 174-179. (3) Liu, Y.; Zhao, J.; Li, Z.; Mu, C.; Ma, W.; Hu, H.; Jiang, K.; Lin, H.; Ade, H.; Yan, H., Aggregation and Morphology Control Enables Multiple Cases of High-Efficiency Polymer Solar Cells. Nat. Commun. 2014, 5, 5293. (4) Heeger, A. J., 25th Anniversary Article: Bulk Heterojunction Solar Cells: Understanding the Mechanism of Operation. Adv. Mater. 2014, 26 (1), 10-28. (5) Lu, L.; Zheng, T.; Wu, Q.; Schneider, A. M.; Zhao, D.; Yu, L., Recent Advances in Bulk Heterojunction Polymer Solar Cells. Chem. Rev. 2015, 115 (23), 12666-12731. (6) You, J.; Dou, L.; Yoshimura, K.; Kato, T.; Ohya, K.; Moriarty, T.; Emery, K.; Chen, C.-C.; Gao, J.; Li, G., A Polymer Tandem Solar Cell with 10.6% Power Conversion Efficiency. Nat. Commun. 2013, 4, 1446. (7) Zhan, X.; Facchetti, A.; Barlow, S.; Marks, T. J.; Ratner, M. A.; Wasielewski, M. R.; Marder, S. R., Rylene and Related Diimides for Organic Electronics. Adv. Mater. 2011, 23 (2), 268284. (8) Kang, H.; Uddin, M. A.; Lee, C.; Kim, K.-H.; Thanh Luan, N.; Lee, W.; Li, Y.; Wang, C.; Woo, H. Y.; Kim, B. J., Determining the Role of Polymer Molecular Weight for HighPerformance All-Polymer Solar Cells: Its Effect on Polymer Aggregation and Phase Separation. J. Am. Chem. Soc. 2015, 137 (6), 2359-2365.


16

Page 17 of 20

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


(9) Nielsen, C. B.; Holliday, S.; Chen, H.-Y.; Cryer, S. J.; McCulloch, I., Non-Fullerene Electron Acceptors for Use in Organic Solar Cells. Acc. Chem. Res. 2015, 48 (11), 2803-2812. (10) Lin, Y.; Zhan, X., Oligomer Molecules for Efficient Organic Photovoltaics. Acc. Chem. Res. 2016, 49 (2), 175-183. (11) Lin, Y.; Zhan, X., Non-fullerene Acceptors for Organic Photovoltaics: an Emerging Horizon. Mater. Horiz. 2014, 1 (5), 470-488. (12) Lin, Y.; Wang, J.; Zhang, Z. G.; Bai, H.; Li, Y.; Zhu, D.; Zhan, X., An Electron Acceptor Challenging Fullerenes for Efficient Polymer Solar Cells. Adv. Mater. 2015, 27 (7), 11701174. (13) Holliday, S.; Ashraf, R. S.; Wadsworth, A.; Baran, D.; Yousaf, S. A.; Nielsen, C. B.; Tan, C.-H.; Dimitrov, S. D.; Shang, Z.; Gasparini, N.; Alamoudi, M.; Laquai, F.; Brabec, C. J.; Salleo, A.; Durrant, J. R.; McCulloch, I., High-efficiency and Air-stable P3HT-based Polymer Solar Cells with a New Non-Fullerene Acceptor. Nat. Commun. 2016, 7, 11585. (14) Yang, Y.; Zhang, Z.-G.; Bin, H.; Chen, S.; Gao, L.; Xue, L.; Yang, C.; Li, Y., Side-Chain Isomerization on an n-type Organic Semiconductor ITIC Acceptor Makes 11.77% High Efficiency Polymer Solar Cells. J. Am. Chem. Soc. 2016, 138 (45), 15011-15018. (15) Zhao, W.; Li, S.; Zhang, S.; Liu, X.; Hou, J., Ternary Polymer Solar Cells based on Two Acceptors and One Donor for Achieving 12.2% Efficiency. Adv. Mater. 2017, 29 (2), 1604059.


17


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

Page 18 of 20

(16) Zhao, F.; Dai, S.; Wu, Y.; Zhang, Q.; Wang, J.; Jiang, L.; Ling, Q.; Wei, Z.; Ma, W.; You, W.; Wang, C.; Zhan, X., Single-Junction Binary-Blend Nonfullerene Polymer Solar Cells with 12.1% Efficiency. Adv. Mater. 2017, 29 (18), 1700144. (17) Lin, Y.; Zhang, Z.-G.; Bai, H.; Wang, J.; Yao, Y.; Li, Y.; Zhu, D.; Zhan, X., Highperformance Fullerene-Free Polymer Solar Cells with 6.31% Efficiency. Energy Environ. Sci. 2015, 8 (2), 610-616. (18) Lin, Y.; He, Q.; Zhao, F.; Huo, L.; Mai, J.; Lu, X.; Su, C.-J.; Li, T.; Wang, J.; Zhu, J.; Sun, Y.; Wang, C.; Zhan, X., A Facile Planar Fused-Ring Electron Acceptor for As-Cast Polymer Solar Cells with 8.71% Efficiency. J. Am. Chem. Soc. 2016, 138 (9), 2973-2976. (19) Baran, D.; Ashraf, R. S.; Hanifi, D. A.; Abdelsamie, M.; Gasparini, N.; Rohr, J. A.; Holliday, S.; Wadsworth, A.; Lockett, S.; Neophytou, M.; Emmott, C. J. M.; Nelson, J.; Brabec, C. J.; Amassian, A.; Salleo, A.; Kirchartz, T.; Durrant, J. R.; McCulloch, I., Reducing the Efficiency-Stability-Cost Gap of Organic Photovoltaics with Highly Efficient and Stable Small Molecule Acceptor Ternary Solar Cells. Nat. Mater. 2017, 16 (3), 363-369. (20) Cheng, P.; Zhang, M.; Lau, T.-K.; Wu, Y.; Jia, B.; Wang, J.; Yan, C.; Qin, M.; Lu, X.; Zhan, X., Realizing Small Energy Loss of 0.55 eV, High Open-Circuit Voltage > 1 V and High Efficiency > 10% in Fullerene-Free Polymer Solar Cells via Energy Driver. Adv. Mater. 2017, 29 (11), 1605216. (21) Liu, Y.; Zhang, Z.; Feng, S.; Li, M.; Wu, L.; Hou, R.; Xu, X.; Chen, X.; Bo, Z., Exploiting Noncovalently Conformational Locking as a Design Strategy for High Performance FusedRing Electron Acceptor Used in Polymer Solar Cells. J. Am. Chem. Soc. 2017, 139 (9), 33563359.


18

Page 19 of 20

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


(22) Liu, F.; Zhou, Z.; Zhang, C.; Vergote, T.; Fan, H.; Liu, F.; Zhu, X., A Thieno 3,4-b thiophene-Based

Non-fullerene

Electron

Acceptor

for

High-Performance

Bulk-

Heterojunction Organic Solar Cells. J. Am. Chem. Soc. 2016, 138 (48), 15523-15526. (23) Lin, Y.; Zhao, F.; Wu, Y.; Chen, K.; Xia, Y.; Li, G.; Prasad, S. K. K.; Zhu, J.; Huo, L.; Bin, H.; Zhang, Z.-G.; Guo, X.; Zhang, M.; Sun, Y.; Gao, F.; Wei, Z.; Ma, W.; Wang, C.; Hodgkiss, J.; Bo, Z.; Inganas, O.; Li, Y.; Zhan, X., Mapping Polymer Donors toward HighEfficiency Fullerene Free Organic Solar Cells. Adv. Mater. 2017, 29 (3), 1604155. (24) Lin, Y.; Zhao, F.; He, Q.; Huo, L.; Wu, Y.; Parker, T. C.; Ma, W.; Sun, Y.; Wang, C.; Zhu, D.; Heeger, A. J.; Marder, S. R.; Zhan, X., High-Performance Electron Acceptor with Thienyl Side Chains for Organic Photovoltaics. J. Am. Chem. Soc. 2016, 138 (14), 49554961. (25) Dai, S.; Zhao, F.; Zhang, Q.; Lau, T.-K.; Li, T.; Liu, K.; Ling, Q.; Wang, C.; Lu, X.; You, W.; Zhan, X., Fused Nonacyclic Electron Acceptors for Efficient Polymer Solar Cells. J. Am. Chem. Soc. 2017, 139 (3), 1336-1343. (26) Wang, M.; Cai, D.; Yin, Z.; Chen, S.-C.; Du, C.-F.; Zheng, Q., AsymmetricIndenothiophene-Based Copolymers for Bulk Heterojunction Solar Cells with 9.14% Efficiency. Adv. Mater. 2016, 28 (17), 3359-3365. (27) Wang, M.; Wang, Z.; Ma, W.; Chen, S.-C.; Zheng, Q., Indenothiophene-Based Wide Bandgap Copolymer for Polymer Fullerene Solar Cells with 9.01% Efficiency and 1.0 V Open Circuit Voltage. Adv. Electron. Mater. 2016, 2 (11), 1600340.


19


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

Page 20 of 20

TOC Graphic


20

PushâPull Type Non-Fullerene Acceptors for Polymer Solar Cells

Recommend Documents

PushâPull Type Non-Fullerene Acceptors for Polymer Solar Cells