Asymmetrical Small Molecule Acceptor Enabling Non-fullerene

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Letter

Asymmetrical Small Molecule Acceptor Enabling Nonfullerene Polymer Solar Cell with Fill Factor Approaching 79% Wei Gao, Tao Liu, Cheng Zhong, Guangye Zhang, Yunpeng Zhang, Ruijie Ming, Lin Zhang, Jingming Xin, Kailong Wu, Yunlong guo, Wei Ma, He Yan, Yunqi Liu, and Chuluo Yang ACS Energy Lett., Just Accepted Manuscript • DOI: 10.1021/acsenergylett.8b00825 • Publication Date (Web): 29 Jun 2018 Downloaded from http://pubs.acs.org on June 29, 2018

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ACS Energy Letters

Asymmetrical Small Molecule Acceptor Enabling Non-fullerene Polymer Solar Cell with Fill Factor Approaching 79% ⊥

Wei Gao†‡#, Tao Liu§*#, Cheng Zhong†#, Guangye Zhang§, Yunpeng Zhang , Ruijie Ming†, Lin Zhangǁ, Jingming Xinǁ, Kailong Wu†, Yunlong Guo⊥, Wei Maǁ*, He Yan§*, Yunqi Liu⊥ and Chuluo Yang†‡* †

Department of Chemistry and Hubei Key Lab on Organic and Polymeric Optoelectronic

Materials, Wuhan University, Wuhan, 430072, People’s Republic of China ‡

College of Materials Science and Engineering, Shenzhen University, Shenzhen, 518060,

People's Republic of China §

Department of Chemistry and Hong Kong Branch of Chinese National Engineering Research

Center for Tissue Restoration & Reconstruction, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong ǁ

State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an

710049, China

ACS Paragon Plus Environment

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⊥

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Beijing National Laboratory for Molecular Sciences, Chinese Academy of Sciences, Beijing

100190, People’s Republic of China #

Those authors contributed equally to this work.

Corresponding Authors *[email protected] *[email protected] *[email protected] *[email protected]

ABSTRACT

Relative to the increase of open-circuit voltage (VOC) and short-circuit current (JSC), promoting fill factor (FF) of the polymer solar cells (PSCs) seems to be more challenging. Here, we designed and synthesized two asymmetrical small molecule acceptors (IDT6CN-M and IDT8CN-M) with large dipole moments. We find that the strong intermolecular interaction and favorable antiparallel packing induced by dipole moment can effectively enhance both lamellar packing and π-π stacking. The PSCs based on PBDB-T:IDT6CN-M and PBDB-T:IDT8CN-M achieved FFs of up to 76.1% and 78.9%, corresponding to the PCEs of 11.23% and 12.43%, respectively. To the best of our knowledge, 78.9% FF is a new record for non-fullerene PSCs. Overall, our work provides a simple and effective molecule designing method to promote FF of non-fullerene PSCs.


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TOC GRAPHICS

-2

Current Density (mA cm )

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ACS Energy Letters

PBDB-T:IDT6CN-M PBDB-T:IDT8CN-M

0 -4 -8 -12 -16 0.0

0.2

0.4

0.6

0.8

1.0

Voltage (V)

As a green technology with the function of converting solar energy into electricity, organic solar cells (OSCs) have shown great potentials in commercial applications thanks to their semitransparency, low-cost, light-weight and roll-to-roll compatible fabrications.1-5 Over the past two decades, research interests on active materials have mainly been focused on the development of high-performance polymeric donors, while fullerene derivatives (e.g. PC61BM and PC71BM) were the dominant choice for electron acceptors.6-13 However, the power conversion efficiencies (PCEs) of polymer solar cells (PSCs) based on fullerenes acceptors did not surpass 12% despite various donors and device configurations being utilized.6,14-18 To solve the dilemma, one of the most effective approaches is to design and synthesize novel non-fullerene small molecule acceptors

(SMAs).19-21

Excitingly,

the

3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-

indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]dithiophene (ITIC)22 family have shown great promise as alternatives to fullerenes. These SMAs possess huge advantages over fullerene acceptors such as their wide absorption range, appropriate lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) energy levels and high electron mobility. PSCs based on the ITIC family SMAs


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have achieved over 13% PCEs to date.23-31 Merits of the molecules that enabled such rapid PCE development lie in the modifiable structure of ITIC that possesses electron-withdrawing end groups,32-38 a ladder-type donor moiety 24,27,29, 39-47 and outstretched side chains48-52, which have allowed precise optimization of the absorption spectra, the frontier orbital levels and the crystallization/aggregation properties. For instance, adding an electron-donating group such as a methyl or a methoxyl group onto the end groups of SMAs could effectively promote the opencircuit voltage (VOC) of the resultant device;32,34 enhancing the electron-donating ability of the donor core24,27,33,39,40,42-46 or optimizing the side group48-52 could significantly increase shortcircuit current (JSC). Impressively, over 1.0 V VOC and 20 mA cm-2 JSC have been realized in single-junction binary non-fullerene PSCs.24,28-31,36,39,45,53-55 In contrast, the other critical factor determining the PCE, namely the high fill factor (FF), is generally lower for non-fullerene PSCs, which imposes severe restrictions on the further enhancement of their PCEs. Despite that various factors contribute to determining the FF, it is generally accepted that optimizing the micromorphology of the bulk heterojunction (BHJ) is beneficial for improving FF.56 In fullerene acceptor-based systems, over 79% FF have been achieved through precisely optimizing polymer donors and nanofiber network of active layer.57,58 In non-fullerene acceptorbased systems, modifiable structures of SMAs allow to introduce bulky moieties (such as IDTN)38 and halogen atoms,23,33,45 such as F and Cl, into the molecular skeleton, which helps to obtain high FFs in OSCs. Molecular design strategies such as introducing C-F…H,59 C-F…S10,60 and C-S…O57 non-covalent interactions, and film processing treatments such as thermal and solvent annealing have been shown able to increase intermolecular packing and molecular ordering, which regulates the morphology. In depth, as proposed by Koster et al., the competition between recombination and extraction of free charges (θ) determines the FF of OSCs.61,62


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ACS Energy Letters

Regulating BHJ morphology to attain high phase purity and balanced mobility has positive effects on reducing recombination rate (krec) and promoting extraction rate (kex), which will obviously lower the θ (θ ∝ krec/kex) value and thus is beneficial to achieve high FF in OSCs. In a recent study, Hou et al. performed calculations on ITIC-like SMAs. It was found that there existed a large dipole moment between the end group and half of the donor unit induced by their strong electron withdrawing and electron-rich nature.53 However, the dipole moment of the whole SMA remains zero. Taking the vector property of dipole moment into consideration, altering the direction of a dipole moment on one half of SMA to make the two internal dipole moments non-collinear can provide the molecule with a large net dipole moment through vector addition. It is well known that the intense interaction induced by the dipole moments between neighboring molecules can strengthen the intermolecular force and enhance the molecular packing. In addition, in order to eliminate the net dipole moment of the whole system, the molecules are possibly forced to pack in an antiparallel pattern,63 which would further enhance molecule packing (Figure S3). Recently, two high-performance asymmetrical SMAs (IDT6CN-M and IDT6CN-Th) with large dipole moment were reported by our group. Dipole-dipole interactions and favorable antiparallel molecule arrangements enable this type of SMAs form strong π-π stacking on the face-on orientation. As a result, the asymmetrical SMAs-based PSCs achieved significantly higher FFs than their symmetrical analogs based- PSCs.64 Guided by the results of the density functional theory (DFT) calculation, we designed and synthesized another asymmetrical SMAs by creating a new asymmetrical ladder-type core of 4,4,9,9-tetrakis(4-hexylphenyl)-4,9-dihydros-indaceno[1,2-b]thiophene[3,2-b]thiophene-alt-[5,6-d]dithieno[3,2-b:2‘,3‘-d]thiophene (IDT8). Even-fuesd-ring donors IDT8 are derived from the 4,4,9,9-tetrakis(4-hexylphenyl)-4,9-dihydro-


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s-indaceno[1,2-b]thiophene-alt-[5,6-d]thieno[3,2-b]thiophene (IDT6) core by incorporating two thiophene units. To provide a good solubility and simultaneously maintain a high VOC, 2-(5/6methyl-3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile (DCI-M) was used as the end group on IDT6 and IDT8 to obtain IDT6CN-M and IDT8CN-M, respectively. As a result, IDT6CN-M and IDT8CN-M both exhibit large dipole moments (~ 7 debye (D)) with two end groups located on same side of the backbone in the optimal conformation, which is totally different from symmetrical SMAs. The PBDB-T:IDT6CN-M- and PBDB-T:IDT8CN-M-based PSCs achieved remarkable FFs of up to 76.1% and 78.9% with PCEs of 11.23% and 12.43%, respectively. Compared with symmetrical IT-M (FF = 73.5%),32 IDT6CN-M- and IDT8CN-M-based PSCs show apparently high FFs, implying that the effectiveness of constructing asymmetrical SMAs with large dipole moments in promoting the FF of non-fullerene PSCs. Moreover, our results also demonstrate that extending the π-conjugated length of asymmetrical SMAs can further promote FF. It should be noted that a FF of 78.9% respresents the highest values in non-fullerene PSCs. To gain deep insights into the SMAs in the molecular level, theoretical calculation on both single and dimer molecules were performed. The geometries were optimized at the B3LYP/def2SVP level with a RIJCOSX approximation65 using the ORCA 4.0 program66 where the long alkyl chains were simplified to methyl. As shown in Figure S1, IDT6CN-M and IDT8CN-M both exhibit excellent planarity with torsion angles smaller than 1 degree. The optimal geometries of IDT6CN-M and IDT8CN-M are that the two end groups are located on the same side of the molecule’s backbone with an intramolecular C-S…O interaction, which results in the formation of a large dipole moment (approaching 7 D) with a direction almost perpendicular to the long axis of the molecular skeleton (Figure S2). The calculated LUMO/HOMO levels are -3.59 eV/-


6

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ACS Energy Letters

5.67 eV for IDT6CN-M and -3.55 eV/-5.53 eV for IDT8CN-M. Extending the π-conjugated length increases the electron-donating ability, leading to a 0.14 eV HOMO energy level promotion from IDT6CN-M to IDT8CN-M. In addition, the asymmetrical structures of two SMAs form an asymmetrical LUMO distribution on the whole acceptor molecule (Figure S1), which may be responsible for the slight LUMO energy level elevation from IDT6CN-M to IDT8CN-M. Obvious HOMO energy level promotion narrows the optical bandgap (Egopt) of IDT8CN-M. Taking the different conformation (two end groups on same side) and dipole moment orientation into consideration, dimer molecules of IDT6CN-M and IDT8CN-M packed in both parallel and antiparallel forms were investigated. As shown in Figure S3, in the parallel packing form, the dimer molecules show certain intersection angles between packing moieties with two dipole moments located on the same side. However, the dimer molecules in the antiparallel packing form (two dipole moments orientated on different sides) exhibit more effective accumulation area due to better overlaps between packing moieties and larger packing length compared to those in the parallel packing form. The s-shaped geometrical configuration of dimer molecules in the antiparallel packing form is more beneficial for the prolongation of the ππ stacking relative to the u-shaped geometrical configuration of dimer molecules in the parallel packing form. Moreover, dimer molecules in antiparallel form own significently lower intermolecular binding energy than that of dimer molecules in parallel form (binding energies of dimer molecules in parallel/antiparallel packing form are -35.1 eV/-36.1 eV for IDT6CN-M and -44.1 eV/-49.0 eV for IDT8CN-M), suggesting a stronger tendency for antiparallel stacking during the course of self-assembly. On the other hand, extending the π-conjugation length significantly increases the packing length and reduces the binding energy of IDT8CN-M, which facilitates intermolecular π-π stacking and thus enhances electron mobility.


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µm

µm

Scheme 1. The synthetic routes, structures and dipole moment (µm) schematic diagrams of asymmetrical IDT6CN-M and IDT8CN-M.

Figure 1. a) Absorption spectra of IDT6CN-M and IDT8CN-M in chloroform solution and neat films. b) Energy levels of PBDB-T, IDT6CN-M and IDT8CN-M.

Table 1. Basic molecular properties of IDT6CN-M and IDT8CN-M.


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ACS Energy Letters

Acceptor

λmaxa) (nm)

λonseta) (nm)

εmaxa) (M-1 cm-1)

λmaxb) (nm)

λonsetb) (nm)

εmaxb) (cm-1)

Egoptc) (eV)

HOMOd) (eV)

LUMOd) (eV)

µee) (cm V-1 s-1)

IDT6CN-M

665

715

2.03 × 105

693

762

1.29 × 105

1.63

-5.62

-3.90

8.98×10-4

IDT8CN-M

681

743

2.25 × 105

699

783

1.35 × 105

1.58

-5.54

-3.91

1.14×10-3

a)

2

In chloroform solution. b)In neat film. c)Calculated from empirical formula: Egopt = 1240/λonset.

d)

Using cyclic voltammetry (CV) method. e)Measured by space charge limited current (SCLC)

method.

The detailed synthetic methods of the two asymmetrical precursors, namely IDT6-CHO and IDT8-CHO, are displayed in Scheme S1. Facile Knoevenagel condensation reactions between IDT8-CHO (IDT6-CHO) and DCI-M were conducted to obtain IDT8CN-M (IDT6CN-M) in a high yield. The two SMAs had been fully characterized and both showed excellent solubility in commonly-used solvents and chemical stability under continuous illumination (Figure S4). As shown in Figure 1a, IDT6CN-M and IDT8CN-M both show a broad absorption range with their maximal absorption at 665 nm and 681 nm in solution, and 693 nm and 699 nm in neat films, respectively. The absorption coefficients in solution and neat films are 2.03 × 105 M-1 cm-1 and 1.29 × 105 cm-1 for IDT6CN-M, and 2.25 × 105 M-1 cm-1 and 1.35 × 105 cm-1 for IDT8CN-M, respectively (Table 1). Moreover, the IDT8CN-M-based blend films also exhibit more intense absorption than that of IDT6CN-M (Figure S5). The redshifted absorption spectrum and high absorption coefficients of IDT8CN-M are beneficial for achieving a high photocurrent. Cyclic voltammetry (CV) was conducted to investigate the frontier molecular orbital (FMO) energy levels of two asymmetrical SMAs. From the CV plots in Figure S6, LUMO/HOMO levels of IDT6CN-M and IDT8CN-M were determined to be -3.90 eV/-5.62 eV and -3.91 eV/-5.54 eV, respectively. It is interesting that extending the π-conjugated length has almost no influence on


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the LUMO energy level but significantly promotes the HOMO energy level of IDT8CN-M, narrowing the Egopt. Charge transport properties for IDT6CN-M and IDT8CN-M thin films in both the horizontal and vertical directions were fully investigated by using measurements of top-gate bottom-contact organic field-effect transistors (OFETs) (Figure S7) and space charge limited current (SCLC) (Figure S8), respectively. The OFET and SCLC electron mobilities are 3.0 × 10-3 cm2 V-1 s-1 and 9.0 × 10-4 cm2 V-1 s-1 for IDT6CN-M, and 9.0 × 10-3 cm2 V-1 s-1 and 1.1 × 10-3 cm2 V-1 s-1 for IDT8CN-M, showing that the electron transport in IDT8CN-M films are better in both directions than that in IDT6CN-M films, which supports our calculation results and is consistent with the morphological characterization shown later. To better understand the structure-property relationship, morphological characterization were carried out. From the atomic force microscope (AFM) studies on the neat films of the SMAs (Figure S9), IDT8CN-M shows a stronger crystallization propensity evidenced by its larger rootmean-square (RMS) roughness (1.63 nm) than IDT6CN-M (0.76 nm). Meanwhile, from the results of the grazing-incidence wide angle X-ray scattering (GIWAXS) study (Table S1), the IDT8CN-M neat film shows a smaller d-spacing and a larger coherence length (CL) than IDT6CN-M in both the lamellar packing and π-π stacking directions, which justifies the higher electron mobility of IDT8CN-M in both horizontal and vertical directions. Comparisons between IDT6CN-M and IDT8CN-M demonstrate that extending the π-conjugated length of asymmetrical SMAs can further enhance the intermolecular interactions and thus promote the crystallization property and electron mobility, which is beneficial for realizing higher FFs and PCEs.


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(b) 80 0

PBDB-T:IDT6CN-M (RT) o PBDB-T:IDT6CN-M (100 C) PBDB-T:IDT8CN-M (RT) o PBDB-T:IDT8CN-M (100 C)

-4

60

EQE (%)

-2


(a)

-8

40 PBDB-T:IDT6CN-M (RT) o PBDB-T:IDT6CN-M (100 C) PBDB-T:IDT8CN-M (RT) o PBDB-T:IDT8CN-M (100 C)

-12 20 -16 -20

0.0

0.2

0.4

0.6

0.8

0 300

1.0

400

Voltage (V)

-2


(d) 10

PBDB-T:IDT6CN-M (RT) PBDB-T:IDT6CN-M (100oC) PBDB-T:IDT8CN-M (RT) PBDB-T:IDT8CN-M (100oC)

1 0.1

Veff (V)

500

600

700

800

Wavelength (nm)

(c) Jph (mA cm-2)

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ACS Energy Letters

1

o

PBDB-T:IDT6CN-M (100 C) S = 0.974 o PBDB-T:IDT8CN-M (100 C) S = 0.974

0.1

1

PBDB-T:IDT6CN-M (RT) S = 0.960 PBDB-T:IDT8CN-M (RT) S = 0.960

10

1

10

100 -2

Light Intensity (mW cm )

Figure 2. a) Current density-voltage (J-V) curves. b) Corresponding EQE spectra. c) Jph versus Veff curves. d) Light intensity dependence of Jsc. Table 2. The photovoltaic parameters of the asymmetrical SMAs-based PCSs. Active layer

VOC (V)a)

JSC (mA cm-2)a)

FF (%)a)

PCE (%)a)

PBDB-T:IDT6CN-Mb)

0.926 (0.925 ± 0.004)

14.90 (14.64 ± 0.15)

72.3 (72.1 ± 0.5)

9.98 (9.76 ± 0.15)

PBDB-T:IDT6CN-Mc)

0.924 (0.920 ± 0.003)

15.97 (15.82 ± 0.16)

76.1 (75.5 ± 0.4)

11.23 (10.99 ± 0.12)

PBDB-T:IDT8CN-Mb)

0.927 (0.925 ± 0.002)

16.10 (15.95 ± 0.11)

72.4 (72.2 ± 0.2)

10.80 (10.65 ± 0.09)

PBDB-T:IDT8CN-Mc)

0.920 (0.920 ± 0.002)

17.11 (16.85 ± 0.22)

78.9 (77.8 ± 0.6)

12.43 (12.06 ± 0.20)

a)

The values in parenthesis are average values and mean square errors calculated from 20 devices.

b)

With 0.5% DIO as solvent additive and no annealing. c)With 0.5% DIO as solvent additive and

an thermal annealing at 100 °C.


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To investigate the photovoltaic performance of the SMAs, a series of PSC devices were fabricated

with

a

structure

of

indium

tin

oxide

(ITO)/poly(3,4-

ethylenedioxythiophene):poly(styrenesulfonate)(PEDOT:PSS)/PBDB-T:acceptor/zirconium acetylacetonate (ZrAcac)/Al, where a wide-bandgap polymer (PBDB-T) was utilized as the electron donor and a commercially available ZrAcac served as efficient cathode interfacial layer (CIL). The well matched energy levels between ZrAcac layer and cathode (Al) is helpful for efficient charge extraction. The detailed device processing conditions can be found in the Supporting Information (Figure S10 and Table S2). The current density-voltage (J-V) curves of the two asymmetrical SMAs-based PSCs are shown in Figure 2a, and the key parameters are listed in Table 2. The two PBDB-T:SMA-based PSCs both exhibit very high FFs, especially for the annealed decives, which are 76.1% for the PBDB-T:IDT6CN-M-based devices and 78.9% for PBDB-T:IDT8CN-M-based devices. These FFs are significantly higher than the FF of the previous PBDB-T:IT-M based devices (73.5%).32 The PBDB-T:IDT8CN-M-based PSCs showed a PCE of up to 12.43%, which is higher than that of the PBDB-T:IDT6CN-M-based devices (11.23%). These results further substantiates our asymmetrical molecular design strategy and the method of extending the π-conjugated length. We note that FF up to 78.9% is the highest values among all non-fullerene PSCs (Table S3). The average values (with mean square errors) calculated from 20 devices (from different fabrication batches) of FFs and PCEs are 75.5 % ± 0.4% and 10.99% ± 0.12% for the PBDB-T:IDT6CN-M-based PSCs, and 77.8% ± 0.6% and 12.06% ± 0.20% for the PBDB-T:IDT8CN-M-based PSCs, indicative of great repeatability of the device fabrication. The detailed photovoltaic parameters of the typical 20 samples are shown in Figure S11 and S12. In addition, the stability of PSCs based on two asymmetrical SMAs was investigated and corresponding stability curves were shown in Figure S13. Two packaged


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ACS Energy Letters

conventional devices in air showed good stability, which can maintain 91% PCE after one day, 76% PCE after five days and 73% PCE after ten days for PBDB-T:IDT6CN-M-based PSCs, and 92% PCE after one day, 81% PCE after five days and 76% PCE after ten days for PBDBT:IDT8CN-M-based PSCs relative to their original PCEs. Comparatively, PSCs based on IDT8CN-M exhibited better stibility than that of IDT6CN-M-based PSCs. The two SMA-based PSCs show similar and high external quantum efficiencies (EQEs) in the range of 300 nm to 750 nm (Figure 2b). The redshifted EQE spectrum provides the PBDB-T:IDT8CN-M-based devices with a larger JSC than the PBDB-T:IDT6CN-M-based devices. The EQE-integrated JSCs are 14.58 mA cm-2 (without annealing) and 15.64 mA cm-2 (with annealing) for the PBDBT:IDT6CN-M-based PSCs, and 15.99 mA cm-2 (without annealing) and 16.95 mA cm-2 (with annealing) for the PBDB-T:IDT8CN-M-based PSCs, which are consistent with the measured JSC with a mismatch factor of only ~2%. The charge transport benhaviors of PBDB-T:IDT6CN-M and PBDB-T:IDT8CN-M blend films were studied by constructing hole-only (ITO/V2O5/active layer/V2O5/Al) and electron-only diodes (ITO/ZnO/active layer/ZrAcac/Al) (Figure S8). For the blend films without annealing, the hole (µh) /electron (µe) mobilities are 6.90 × 10-4 cm2 V-1 s-1/4.25 × 10-4 cm2 V-1 s-1 for PBDB-T:IDT6CN-M (µh/µe = 1.62), and 7.45 × 10-4 cm2 V-1 s-1/4.67 × 10-4 cm2 V-1 s-1 for PBDB-T:IDT8CN-M (µh/µe = 1.59). After annealing, the hole/electron mobilities increased to 9.84 × 10-4 cm2 V-1 s-1/5.85 × 10-4 cm2 V-1 s-1 for the PBDB-T:IDT6CN-M-based blend films with a µh/µe of 1.68, and 1.05 × 10-3 cm2 V-1 s-1/6.7 × 10-4 cm2 V-1 s-1 for the PBDB-T:IDT8CNM-based blend films with a µh/µe of 1.57. In comparsion, both the PBDB-T:IDT6CN-M- and PBDB-T:IDT8CN-M-based blend films show higher and more balanced carriers mobilities than the PBDB-T:IT-M32 (refered to the reported results) based blend films, which is favorble for


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IDT6CN-M and IDT8CN-M to obtain higher FFs in PSCs. In addition, the PBDB-T:IDT8CNM-based blend films exhibit sightly higher and more balanced carrier mobilities than the PBDBT:IDT6CN-M-based blend films, which is consistent with the higher FFs observed in the PBDBT:IDT8CN-M-based devices. The exciton dissociation and charge extraction of the two asymmetrical SMAs-based PSCs were invesigated by plotting the the photocurrent (Jph) against the effective applied voltage (Veff) (Figure 2c). The saturated Jph (Jsat) occurred at a reverse voltage greater than 2 V for both devices. For the devices without and with annealing, the Jsat are 15.67 mA cm-2 and 16.50 mA cm-2 for the PBDB-T:IDT6CN-M-based PSCs, and 16.91 mA cm-2 and 17.74 mA cm-2 for the PBDB-T:IDT8CN-M-based PSCs, respectively, suggesting that extending the π-conjugated length could achieve a larger Jsat. Moreover, the PBDB-T:IDT6CNM- and PBDB-T:IDT8CN-M-based PSCs show very similar and high exciton dissociation (95%97%) and charge collection probabilities (82%-90%) (Table S4), well illuminating the large JSCs and high FFs of two PSCs without and with annealing. The photocurrent (Jph) as a function of light intensities (P) was also measured to understand the bimolecular recombination in the two asymmetrical SMAs-based PSCs. As shown in Figure 2d, a highly linear dependence of JSC on P can be observed in both PBDB-T:IDT6CN-M- and PBDB-T:IDT8CN-M-based PSCs with high and similar slopes without or with annealing, indicative of low bimolecular recombination, which is important for the realization of high JSC and FF. Extending the π-conjugated length of IDT6CN-M does not down-shift the LUMO energy level of IDT8CN-M, that is to say the internal voltages (Vint) of PBDB-T:IDT6CN-M- and PBDB-T:IDT8CN-M-based PSCs keep the same, but significently enhances the electron mobility of PBDB-T:IDT8CN-M blend and thus accelerates the charge extraction, which well confirms the higher charge collection probability of PBDB-T:IDT8CN-M-based PSCs before and after annealing. Assuming that two PSCs own


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same recombination rate evidenced by the similar phase purity and bimolecular recombination, a smaller θ value will occur in PBDB-T:IDT8CN-M-based PSCs, and thus can achieve higher FF before and after annealing treatment.61 Those results suggest that enlarging the π-conjugated length of asymmetrical SMAs can further promote its FF when applied in OSCs.

Figure 3. The AFM height sensor images (2 µm × 2 µm) for: a) a PBDB-T:IDT6CN-M blend film; b) a PBDB-T:IDT8CN-M blend film; c) a PBDB-T:IDT6CN-M blend film annealed at 100 °C; d) a PBDB-T:IDT8CN-M blend film annealed at 100 °C. e) RSoXS profiles of PBDBT:IDT6CN-M and PBDB-T:IDT8CN-M-based blend films without and with annealing.

AFM and resonant soft X-ray scattering (RSoXS) experiments were carried out to gain deep insights into the micromorphology of BHJ active layer. As shown in Figure 3a-d, the PBDBT:IDT6CN-M- and PBDB-T:IDT8CN-M-based active layers both show smooth and uniform morphology with small RMS roughness (1.15 nm - 1.40 nm). Nanofiber structures and bicontinuous interpenetrating networks can be distinctly observed without and with annealing (Figure S9). RSoXS results (Figure 3e) reveal that the annealing treatment not only reduces the


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domain size of the two blend films but also enhances the domain purity of the two blends (Table S1), which is favourable for promoting carrier mobility, JSC and FF of the PSCs. The similar and favorable morphology, along with reasonably small domain sizes and high domain purity for the two asymmetrical SMAs-based active layers contribute to their similar, efficient exciton dissociation and high charge collection probabilities as well as low bimolecular recombination, which in turn gives rise to the high FF of two PSCs.

Figure 4. The 2D GIWAXS patterns for: a) a IDT6CN-M neat film; b) a IDT8CN-M neat film; c) a PBDB-T:IDT6CN-M blend film; d) a PBDB-T:IDT8CN-M blend film; e) a PBDB-T:IDT6CNM blend film annealed at 100oC; f) a PBDB-T:IDT8CN-M blend film annealed at 100oC. g) Corresponding in-plane and out-of-plane cut-line profiles. To further understand the molecular packing of two asymmetrical SMAs in neat and blend films and the role of annealing treament, GIWAXS experiments were performed. The 2DGIWAXS patterns and the corresponding in-plane and out-of-plane cut-line profiles are displayed in Figure 4. Both IDT6CN-M and IDT8CN-M exhibit strong (010) diffraction peaks in the qz direction (Figure 4a-b) located at 1.80 Å-1 and 1.82 Å-1, respectively, indicative of a


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ACS Energy Letters

typical face-on orientation. The d-spacing and CL calculated from the π-π stacking peaks are 3.47 Å and 24.52 Å for the IDT6CN-M neat film, and 3.45 Å and 26.81 Å for the IDT8CN-M neat film (Table S1), suggesting that IDT8CN-M possesses a stronger crystallization propensity than IDT6CN-M, which is consistent with the larger phase separation of IDT8CN-M neat film. The smaller d-spacing and longer CLs in both lamellar packing and π-π stacking direction are beneficial for IDT8CN-M to obtain a higher electron mobility than IDT6CN-M. When it comes to the morphology of the blend films, both blends adopt dominant face-on orientation with intense (010) diffraction peaks coming from both polymer donor and SMA. The (010) CLs for the films without and with annealing are 23.74 Å and 24.61 Å, respectively, for PBDBT:IDT6CN-M, and 22.14 Å and 24.56 Å, respectively, for PBDB-T:IDT8CN-M. The fact that annealing hardly changes their CL indicates that the π-π stackings of the PBDB-T:IDT6CN-M and PBDB-T:IDT8CN-M blend films are in a relatively stable state. The similar and stable π-π stackings of two asymmetrical SMAs-based blend films may be caused by their favorable antiparallel packing form. In contrast, the effect of annealing on the CLs of the lamellar packing is significant, evidenced by the increase from 83.63 Å (without annealing) to 100.32 Å (with annealing) for PBDB-T:IDT6CN-M and from 82.28 Å (without annealing) to 102.17 Å (with annealing) for PBDB-T:IDT8CN-M. One hypothesis is that annealing accelerates the vibration of SMAs and may make the arrangement of cancelled out dipole moments more ordered (i.e., more ordered molecule arrangement in the qxy plane), which could contribute to the enhanced domain purity and significantly promoted FFs of two asymmetrical SMAs-based PSCs. In conclusion, two asymmetrical SMAs called IDT6CN-M and IDT8CN-M with large dipole moments were designed and synthesized by respectively embracing asymmetrical ladder-type core of IDT6 and IDT8. Compared with IDT6CN-M, IDT8CN-M shows a redshifted absorption,


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a similar LUMO energy level and a higher electron mobility. Theoretical calculations revealed that the dipole-induced antiparallel packing form can lead to more favorable molecular ordering than that the parallel packing form does. The PBDB-T:IDT6CN-M- and PBDB-T:IDT8CN-Mbased active layers exhibited similar exciton dissociation and charge collection probabilities, bimolecular recombinations and micromorphologies with and without annealing, but PBDBT:IDT8CN-M showed slightly more optimized parameters than PBDB-T:IDT6CN-M on all these aspects. Consequently, the PSCs based on PBDB-T:IDT6CN-M and PBDB-T:IDT8CN-M achieved PCEs of 11.23% and 12.43% with similar VOCs and very high FFs of up to 76.1% and 78.9%, respectively. To the best of our knowledge, FF approaching 78.9% resprents the highest values among non-fullerene PSCs. In addition, the role of annealing is mainly to enhance the coherence length of lamellar packing and promote domain purity of two asymmetrical SMAsbased active layers. These results allow us to conclude that designing asymmetrical SMA can serve as an effective methodology to promote FF of PSCs and that extending the π-conjugated length of asymmetrical SMAs can further promote FF and PCE. ASSOCIATED CONTENT Supporting Information. Materials synthesis; DFT calculations; devices fabrications; CV, OFET and SCLC measurements and 1H and 13C NMR spectra AUTHOR INFORMATION The authors declare no competing financial interest. ACKNOWLEDGMENT


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This work was financially supported by the National Natural Science Foundation of China (No. 21572171, 21504066 and 21534003), the National Basic Research Program of China (973 Program project numbers 2013CB834701 and 2014CB643501), Shenzhen Peacock Plan (KQTD20170330110107046), the Shenzhen Technology and Innovation Commission (project number

JCYJ20170413173814007),

Ministry

of

science

and

technology

(No.

2016YFA0200700). X-ray data was acquired at beamlines 7.3.3 and 11.0.1.2 at the Advanced Light Source. The authors thank Chenhui Zhu at beamline 7.3.3, and Cheng Wang at beamline 11.0.1.2 for assistance with data acquisition.

REFERENCES (1) Yu, G.; Cao, J.; Hummelen, J. C.; Wuld, F.; Heeger, A. J. Polymer Photovoltaic Cells: Enhanced Efficiencies via a Network of Internal Donor-Acceptor Heterojunctions. Science 1995, 270, 1789-1791. (2) Li, G.; Zhu, R.; Yang, Y. Polymer Solar Cells. Nat. Photonics 2012, 6, 153-161. (3) Yao, H.; Ye, L.; Zhang, H.; Li, S.; Zhang, S.; Hou, J. Molecular Design of Benzodithiophene-Based Organic Photovoltaic Materials. Chem. Rev. 2016, 116, 7397-7457. (4) Thompson, B. C.; Fréchet, J. M. J. Polymer–Fullerene Composite Solar Cells. Angew. Chem. Int. Ed. 2008, 47, 58-77. (5) Li, Z.; Xu, X.; Zhang, W.; Meng, X.; Genene, Z.; Ma, W.; Mammo, W.; Yartsev, A.; Andersson, M. R.; Janssen, R. A. J.; Wang, E. 9.0% Power Conversion Efficiency from Ternary All-Polymer Solar Cells. Energy Environ. Sci. 2017, 10, 2212.


19


Page 20 of 29

(6) Zhao, J.; Li, Y.; Yang, G.; Jiang, K.; Lin, H.; Ade, H.; Ma, W.; Yan, H. Efficient Organic Solar Cells Processed from Hydrocarbon Solvents. Nat. Energy 2015, 1, 15027. (7) Huo, L.; Liu, T.; Fan, B.; Zhao, Z.; Sun, X.; Wei, D.; Yu, M.; Liu, Y.; Sun, Y. Organic Solar Cells Based on a 2D Benzo[1,2-b:4,5-b']-difuran-Conjugated Polymer with High-Power Conversion Efficiency. Adv. Mater. 2015, 27, 6969-6975. (8) Wang, M.; Hu, X.; Liu, P.; Li, W.; Gong, X.; Huang, F.; Cao, Y. Donor-Acceptor Conjugated Polymer Based on Naphtho[1,2-c:5,6-c]bis[1,2,5]thiadiazole for HighPerformance Polymer Solar Cells. J. Am. Chem. Soc. 2011, 133, 9638-9641. (9) Cao, J.; Liao, Q.; Du, X.; Chen, J.; Xiao, Z.; Zuo, Q.; Ding, L. A Pentacyclic Aromatic Lactam Building Block for Efficient Polymer Solar Cells. Energy Environ. Sci. 2013, 6, 3224-3228. (10)

Price, S. C.; Stuart, A. C.; Yang, L.; Zhou, H.; You, W. Fluorine Substituted Conjugated

Polymer of Medium Band Gap Yields 7% Efficiency in Polymer-Fullerene Solar Cells. J. Am. Chem. Soc. 2011, 133, 4625-4631. (11)

Tao, Q.; Liu, T.; Duan, L.; Cai, Y.; Xiong, W.; Wang, P.; Tan, H.; Lei, G.; Pei, Y.; Zhu,

W.; et al. Wide Bandgap Copolymers with Vertical Benzodithiophene Dicarboxylate for High-Performance Polymer Solar Cells with an Efficiency up to 7.49%. J. Mater. Chem. A 2016, 4, 18792-18803. (12)

Wang, E.; Mammo, W.; Andersson, M. R. 25th Anniversary Article: Isoindigo-Based

Polymers and Small Molecules for Bulk Heterojunction Solar Cells and Field Effect Transistors. Adv. Mater. 2014, 26, 1801-1826.


20

Page 21 of 29 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 Energy Letters

(13)

Fan, Q.; Su, W.; Guo, X.; Guo, B.; Li, W.; Zhang, Y.; Wang, K.; Zhang, M.; Li, Y. A

New Polythiophene Derivative for High Efficiency Polymer Solar Cells with PCE over 9%. Adv. Energy Mater. 2016, 6, 1600430. (14)

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, 174-179. (15)

Vohra, V.; Kawashima, K.; Kakara, T.; Koganezawa, T.; Osaka, I.; Takimiya, K.;

Murata, H. Efficient Inverted Polymer Solar Cells Employing Favourable Molecular Orientation. Nat. Photonics 2015, 9, 403-408. (16)

Nain, L.; Zhang, W.; Zhu, N.; Liu, L.; Xie, Z.; Wu, H.; Würthner, F.; Ma, Y.

Photoconductive Cathode Interlayer for Highly Efficient Inverted Polymer Solar Cells. J. Am. Chem. Soc. 2015, 137, 6995-6998. (17)

Zhou, H.; Zhang, Y.; Mai, C.-K.; Collins, S. D.; Bazan, G. C.; Nguyen, T.-Q.; Heeger, A.

J. Polymer Homo-Tandem Solar Cells with Best Efficiency of 11.3%. Adv. Mater. 2015, 27, 1767-1773. (18)

Chen, C.-C.; Chang, W.-H.; Yoshimura, K.; Ohya, K.; You, J.; Gao, J.; Hong, Z.; Yang,

Y. An Efficient Triple-Junction Polymer Solar Cell Having a Power Conversion Efficiency Exceeding 11%. Adv. Mater. 2014, 26, 5670-5677. (19)

Baran, D.; Ashraf, R. S.; Hanifi, D. A.; Abdelsamie, M.; Gasparini, N.; Röhr, J. A.;

Holliday, S.; Wadsworth, A.; Lockett, S.; Neophytou, M.; et al. Reducing the Efficiency-


21


Page 22 of 29

Stability-Cost Gap of Organic Photovoltaics with Highly Efficient and Stable Small Molecule Acceptor Ternary Solar Cells. Nat. Materials 2017, 16, 363-369. (20)

Yan, C.; Barlow, S.; Wang, Z.; Yan, H.; Jen, A. K.-Y.; Marder, S. R.; Zhan, X. Non-

fullerene Acceptors for Organic Solar Cells. Nat. Rev. Mater. 2018, 3, 18003. (21)

Lin, Y.; Zhan, X. Non-fullerene Acceptors for Organic Photovoltaics: an Emerging

Horizon. Mater. Horiz. 2014, 1, 470-488. (22)

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, 1170-1174. (23)

Zhao, W.; Li, S.; Yao, H.; Zhang, S.; Zhang, Y.; Yang, B.; Hou, J. Molecular

Optimization Enables over 13% Efficiency in Organic Solar Cells. J. Am. Chem. Soc. 2017, 139, 7148-7151. (24)

Xiao, Z.; Jia, X.; Ding, L. Ternary Organic Solar Cells Offer 14% power Conversion

Efficiency. Science Bulletin 2017, 62, 1562-1564. (25)

Xu, X.; Yu, T.; Bi, Z.; Ma, W.; Li, Y.; Peng, Q. Realizing Over 13% Efficiency in Green-

Solvent-Processed Nonfullerene Organic Solar Cells Enabled by 1,3,4-Thiadiazole-Based Wide-Bandgap Copolymers. Adv. Mater. 2017, 29, 1703973. (26)

Cui, Y.; Yao, H.; Gao, B.; Qin, Y.; Zhang, S.; Yang, B.; He, C.; Xu, B.; Hou, J. Fine-

Tuned Photoactive and Interconnection Layers for Achieving over 13% Efficiency in a Fullerene-Free Tandem Organic Solar Cell. J. Am. Chem. Soc. 2017, 139, 7302-7309. (27)

Fei, Z.; Eisner, F. D.; Jiao, X.; Azzouzi, M.; Röhr, J. A.; Han, Y.; Shahid, M.; Chesman,

A. S. R.; Easton, C. D.; MeNeill, C. R.; et al. An Alkylated Indacenodithieno[3,2-


22

Page 23 of 29 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 Energy Letters

b]thiophene-Based Nonfullerene Acceptor with High Crystallinity Exhibiting Single Junction Solar Cell Efficiencies Greater than 13% with Low Voltage Losses. Adv. Mater. 2018, 30, 1705209. (28)

Fan, Q.; Zhu, Q.; Xu, Z.; Su, W.; Chen, J.; Wu, J.; Guo, X.; Ma, W.; Zhang, M.; Li, Y.

Chlorine Substituted 2D-Conjugated Polymer for High-Performance Polymer Solar Cells with 13.1% Efficiency via Toluene Processing. Nano Energy 2018, 48, 413-420. (29)

Wang, W.; Zhao, B.; Cong, Z.; Xie, Y.; Wu, H.; Liang, Q.; Liu, S.; Liu, F.; Gao, C.; Wu,

H.; Cao, Y. Nonfullerene Polymer Solar Cells Based on a Main-Chain Twisted LowBandgap Acceptor with Power Conversion Efficiency of 13.2%. ACS Energy Lett. 2018, 3, 1499-1507. (30)

Zhang, S.; Qin, Y.; Zhu, J.; Hou, J. Over 14% Efficiency in Polymer Solar Cells Enabled

by a Chlorinated Polymer Donor. Adv. Mater. 2018, 30, 1800868. (31)

Li, S.; Ye, L.; Zhao, W.; Yan, H.; Yang, B.; Liu, D.; Li, W.; Ade, H.; Hou, J. A Wide

Band Gap Polymer with a Deep Highest Occupied Molecular Orbital Level Enables 14.2% Efficiency in Polymer Solar Cells. J. Am. Chem. Soc. 2018, 140, 7159-7167. (32)

Li, S.; Ye, L.; Zhao, W.; Zhang, S.; Mukherjee, S.; Ade, H.; Hou, J. Energy-Level

Modulation of Small-Molecule Electron Acceptors to Achieve over 12% Efficiency in Polymer Solar Cells. Adv. Mater. 2016, 28, 9423-9429. (33)

Dai, S.; Zhao, F.; Zhang, Q.; Lau, T.-K.; Li, T.; Liu, K.; Ling, Q.; Wang, C.; Lu, X.; You,

W.; et al. Fused Nonacyclic Electron Acceptors for Efficient Polymer Solar Cells. J. Am. Chem. Soc. 2017, 139, 1336-1343.


23


(34)

Page 24 of 29

Li, S.; Ye, L.; Zhao, W.; Zhang, S.; Ade, H.; Hou, J. Significant Influence of the

Methoxyl Substitution Position on Optoelectronic Properties and Molecular Packing of Small-Molecule Electron Acceptors for Photovoltaic Cells. Adv. Energy Mater. 2017, 7, 1700183. (35)

Xie, D.; Liu, T.; Gao, W.; Zhong, C.; Huo, L.; Luo, Z.; Wu, K.; Xiong, W.; Liu, F.; Sun,

Y.; et al. A Novel Thiophene-Fused Ending Group Enabling an Excellent Small Molecule Acceptor for High-Performance Fullerene-Free Polymer Solar Cells with 11.8% Efficiency. Sol. RRL 2017, 1, 1700044. (36)

Yao, H.; Ye, L.; Hou, J.; Jang, B.; Han, G.; Cui, Y.; Su, G. M.; Wang, C.; Gao, B.; Yu,

R.; et al. Achieving Highly Efficient Nonfullerene Organic Solar Cells with Improved Intermolecular Interaction and Open-Circuit Voltage. Adv. Mater. 2017, 29, 1700254. (37)

Luo, Z.; Bin, H.; Liu, T.; Zhang, Z.-G.; Yang, Y.; Zhong, C.; Qiu, B.; Li, G.; Gao, W.;

Xie, D.; et al. Fine-Tuning of Molecular Packing and Energy Level through Methyl Substitution Enabling Excellent Small Molecule Acceptors for Nonfullerene Polymer Solar Cells with Efficiency up to 12.54%. Adv. Mater. 2018, 30, 1706124. (38)

Li, S.; Ye, L.; Zhao, W.; Liu, X.; Zhu, J.; Ade, H.; Hou, J. Design of a New Small-

Molecule Electron Acceptor Enables Efficient Polymer Solar Cells with High Fill Factor. Adv. Mater. 2017, 29, 1704051. (39)

Yao, Z.; Liao, X.; Gao, K.; Lin, K.; Xu. X.; Shi, X.; Zuo, L.; Liu, F.; Chen, Y.; Jen, A.

K.-Y. Dithienopicenocarbazole-Based Acceptors for Efficient Organic Solar Cells with Optoelectronic Response Over 1000 nm and an Extremely Low Energy Loss. J. Am. Chem. Soc. 2018, 140, 2054-2057.


24

Page 25 of 29 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 Energy Letters

(40)

Li, T.; Dai, S.; Ke, Z.; Yang, L.; Wang, J.; Yan, C.; Ma, W.; Zhan, X. Fused

Tris(thienothiophene)-Based Electron Acceptor with Strong Near-Infrared Absorption for High-Performance As-Cast Solar Cells. Adv. Mater. 2018, 30, 1705969. (41)

Li, S.; Zhan, L.; Liu, F.; Ren, J.; Shi, M.; Li, C.-Z.; Russell, T. P.; Chen, H. An Unfused-

Core-Based Nonfullerene Acceptor Enables High-Efficiency Organic Solar Cells with Excellent Morphological Stability at High Temperatures. Adv. Mater. 2017, 29, 1705208. (42)

Kan, B.; Zhang, J.; Liu, F.; Wan, X.; Li, C.; Ke, X.; Wang, Y.; Feng, H.; Zhang, Y.;

Long, G.; et al. Fine-Tuning the Energy Levels of a Nonfullerene Small-Molecule Acceptor to Achieve a High Short-Circuit Current and a Power Conversion Efficiency over 12% in Organic Solar Cells. Adv. Mater. 2018, 30, 1704904. (43)

Zhu, J.; Ke, Z.; Zhang, Q.; Wang, J.; Dai, S.; Wu, Y.; Xu, Y.; Lin, Y.; Ma, W.; You, W.;

et al. Naphthodithiophene-Based Nonfullerene Acceptor for High-Performance Organic Photovoltaics: Effect of Extended Conjugation. Adv. Mater. 2018, 30, 1704713. (44)

Xu, S.; Zhou, Z.; Liu, W.; Zhang, Z.; Liu, F.; Yan, H.; Zhu, X. A Twisted Thieno[3,4-

b]thiophene-Based Electron Acceptor Featuring a 14-π-Electron Indenoindene Core for High-Performance Organic Photovoltaics. Adv. Mater. 2017, 29, 1704501. (45)

Li, Y.; Lin, J.-D.; Che, X.; Qu, Y.; Liu, F.; Liao, L.-S.; Forrest, S. R. High Efficiency

Near-Infrared and Semitransparent Non-Fullerene Acceptor Organic Photovoltaic Cells. J. Am. Chem. Soc. 2017, 139, 17114-17119.


25


(46)

Page 26 of 29

Wang, J.; Wang, W.; Wang, X.; Wu, Y.; Zhang, Q.; Yan, C.; Ma, W.; You, W.; Zhan, X.

Enhancing Performance of Nonfullerene Acceptors via Side-Chain Conjugation Strategy. Adv. Mater. 2017, 29, 1702125. (47)

Dai, S.; Li, T.; Wang, W.; Xiao, Y.; Lau, T.-K.; Li, Z.; Liu, K.; Lu, X.; Zhan, X.

Enhancing the Performance of Polymer Solar Cells via Core Engineering of NIR-Absorbing Electron Acceptors. Adv. Mater. 2018, 30, 1706571. (48)

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, 15011-15018. (49)

Feng, S.; Zhang, C.; Liu, Y.; Bi, Z.; Zhang, Z.; Xu, X.; Ma, W.; Bo, Z. Fused-Ring

Acceptors with Asymmetrical Side Chains for High-Performance Thick-Film Organic Solar Cells. Adv. Mater. 2017, 29, 1703527. (50)

Lin, Y.; Zhao, F.; He, Q.; Huo, L.; Wu, Y.; Parker, T. C.; Ma, W.; Sun, Y.; Wang, C.;

Zhu, D.; et al. High-Performance Electron Acceptor with Thienyl Side Chains for Organic Photovoltaics. J. Am. Chem. Soc. 2016, 138, 4955-4961. (51)

Gao, W.; An, Q.; Ming, R.; Xie, D.; Wu, K.; Luo, Z.; Zou, Y.; Zhang, F.; Yang, C. Side

Group Engineering of Small Molecular Acceptors for High-Performance Fullerene-Free Polymer Solar Cells: Thiophene Being Superior to Selenophene. Adv. Funct. Mater. 2017, 27, 1702194. (52)

Fan, Q.; Wang, Y.; Zhang, M.; Wu, B.; Guo, X.; Jiang, Y.; Li, W.; Guo, B.; Ye, C.; Su,

W.; et al. High-Performance As-Cast Nonfullerene Polymer Solar Cells with Thicker Active


26

Page 27 of 29 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 Energy Letters

Layer and Large Area Exceeding 11% Power Conversion Efficiency. Adv. Mater. 2018, 30, 1704546. (53)

Yao, H.; Cui, Y.; Yu, R.; Gao, B.; Zhang, H.; Hou, J. Design, Synthesis, and Photovoltaic

Characterization of a Small Molecular Acceptor with an Ultra-Narrow Band Gap. Angew. Chem. Int. Ed. 2017, 56, 3045-3049. (54)

Xu, X.; Li, Z.; Zhang, W.; Meng, X.; Zou, X.; Rasi, D. D. C.; Ma, W.; Yartsev, A.;

Andersson, M. R.; Janssen, R. A. J.; Wang, E. 8.0% Efficient All-Polymer Solar Cells with High Photovoltage of 1.1 V and Internal Quantum Efficiency near Unity. Adv. Energy Mater. 2018, 8, 1700908. (55)

Fan, Q.; Xu, Z.; Guo, X.; Meng, X.; Li, W.; Su, W.; Ou, X.; Ma, W.; Zhang, M.; Li, Y.

High-Performance Nonfullerene Polymer Solar Cells with Open-Circuit Voltage over 1 V and Energy Loss as Low as 0.54 eV. Nano Energy 2017, 40, 20-26. (56)

Oosterhout, S. D.; Wienk, M. M.; Bavel, S. S.; Thiedmann, R.; Koster, L. J. A.; Gilot, J.;

Loos, J.; Schmidt, V.; Janssen, R. A. J. The Effect of Three-Dimensional Morphology on the Efficiency of Hybrid Polymer Solar Cells. Nat. Mater. 2009, 8, 818-824. (57)

Guo, X.; Zhou, N.; Lou, S. J.; Smith, J.; Tice, D. B.; Hennek, J. W.; Ortiz, R. P.;

Navarrete, J. T. L.; Li, S.; Strzalka, J.; Chen, L. X.; et al. Polymer Solar Cells with Enhanced Fill Factors. Nat. Photonics 2013, 7, 825-833. (58)

Liu, T.; Huo, L.; Chandrabose, S.; Chen, K.; Han, G.; Qi, F.; Meng, X.; Xie, D.; Ma, W.;

Yi, Y.; et al. Optimized Fibril Network Morphology by Precise Side-Chain Engineering to


27


Page 28 of 29

Achieve High-Performance Bulk-Heterojunction Organic Solar Cells. Adv. Mater. 2018, 30, 1707353. (59)

Zhao, F.; Dai, S.; Wu, Y.; Zhang, Q.; Wang, J.; Jiang, L.; Ling, Q.; Wei, Z.; Ma, W.;

You, W.; al et. Single-Junction Binary-Blend Nonfullerene Polymer Solar Cells with 12.1% Efficiency. Adv. Mater. 2017, 29, 1700144. (60)

Wolf, J.; Cruciani, F.; Labban, A. E.; Beaujuge, P. M. Wide Band-Gap 3,4-

Difluorothiophene-Based Polymer with 7% Solar Cell Efficiency: An Alternative to P3HT. Chem. Mater. 2015, 27, 4184-4187. (61)

Bartesaghi, D.; Pérez, I. D. C.; Kniepert, J.; Roland, S.; Turbiez, M.; Neher, D.; Koster, L.

J. A. Competition between Recombination and Extraction of Free Charges Determines the Fill Factor of Organic Solar Cells. Nat. Commun. 2015, 6, 7083. (62)

Neher, D.; Kniepert, J.; Elimelech, A.; Koster, L. J. A. A New Figure of Merit for

Organic Solar Cells with Transport-limited Photocurrents. Sci. Rep. 2016, 6, 24861. (63)

Li, Z.; Zhu, Z.; Chueh, C.-C.; Jo, S. B.; Luo, J.; Jang, S.-H.; Jen, A. K.-Y. Rational

Design of Dipole Chromophore as an Efficient Dopant-Free Hole-Transporting Material for Perovskite Solar Cells. J. Am. Chem. Soc. 2016, 138, 11833-11839. (64)

Gao, W.; Zhang, M.; Liu, T.; Ming, R.; An, Q.; Wu, K.; Xie, D.; Luo, Z.; Zhong, C.; Liu,

F.; et al. Asymmetrical Ladder-Type Donor-Induced Polar Small Molecule Acceptor to Promote Fill Factors Approaching 77% for High-Performance Nonfullerene Polymer Solar Cells. Adv. Mater. 2018, 30, 1800052.


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ACS Energy Letters

(65)

Neese, F.; Wennmohs, F.; Hansen, A.; Becker, U. Efficient, Approximate and Parallel

Hartree–Fock and Hybrid DFT Calculations. A 'Chain-of-Spheres' Algorithm for the Hartree–Fock Exchange. Chem. Phys. 2009, 356, 98-109. (66)

Neese, F. The ORCA Program System. WIREs Comput. Mol. Sci. 2012, 2, 73-78.


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Asymmetrical Small Molecule Acceptor Enabling Non-fullerene

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