Perylene Diimide-Based Zwitterion as the Cathode Interlayer for High

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Organic Electronic Devices

A Perylenediimide-Based Zwitterion as the Cathode Interlayer for High Performance Non-Fullerene Polymer Solar Cells Changjian Song, Xiaohui Liu, Xiaodong Li, Ying-Chiao Wang, Li Wan, Xiaohua Sun, Wenjun Zhang, and Junfeng Fang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b01147 • Publication Date (Web): 10 Apr 2018 Downloaded from http://pubs.acs.org on April 10, 2018

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ACS Applied Materials & Interfaces

A Perylenediimide-Based Zwitterion as the Cathode Interlayer for High Performance Non-Fullerene Polymer Solar Cells Changjian Song,a,b Xiaohui Liu,a Xiaodong Li,a Ying-Chiao Wang,a Li Wan,a Xiaohua Sunc, Wenjun Zhang,*a,b and Junfeng Fang*a,b a

Ningbo Institute of Materials Technology and Engineering, Chinese Academy of

Sciences, Ningbo 315201, China.

b

University of Chinese Academy of Sciences, 19 A Yuquan Rd, Shijingshan District,

Beijing 100049, China.

c

College of Materials and Chemical Engineering, Key Laboratory of Inorganic

Nonmetallic Crystalline and Energy Conversion Materials, China Three Gorges University, Yichang 443002, China.

E-mail: [email protected] and [email protected].

ACS Paragon Plus Environment

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ABSTRACT Non-fullerene polymer solar cells (PSCs) have earned widespread and intense interest on account of their properties of tunable energy levels, potential for low-cost production processes, reduced energy losses and strong light absorption coefficients. Here, a water/alcohol-soluble zwitterion perylene diimide zwitterion (PDI-z) consisted of sulfobetaine ion as a terminal substituent and perylene diimides as a conjugated core was synthesized. PDI-z was employed as electron transport layer (ETL) for non-fullerene PSC devices, obtaining an optimal power conversion efficiency (PCE) above 11.23%. Moreover, non-fullerene PSCs with PDI-z cathode interlayer displayed an excellent performance on a large scale of interlayer thickness, which was compatible with printing fabrication techniques. Additionally, PDI-z interlayer presented good ability of modifying high work function (WF) metals (for instance, Au, Cu, Ag) in non-fullerene devices and Ag device displayed a PCE of 9.38%. This work provides a well alternative ETL for high efficiency non-fullerene PSCs. KEYWORD:

electron

transport

layer

(ETL),

small-molecule

non-fullerene polymer solar cells, thickness insensitivity, high WF metals,


zwitterion,

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1. INTRODUCTION On account of the potentials e.g., large-area solution processing, flexible, lightweight and low cost,1-6 bulk heterojunction (BHJ) polymer solar cells (PSCs) have drawn tremendous attention. Typically, a BHJ active layer is consisted of interpenetrating donor and acceptor.7-9 Recently, PSCs based on non-fullerene accepters have made huge progress.3, 10-13 Meanwhile, a power conversion efficiency (PCE) above 13% has been recorded.11 Non-fullerene accepters possess the properties of tunable energy levels, potential for low-cost production processes, reduced energy losses and strong light absorption coefficients.14-17 All of these advantages indicate that non-fullerene accepters present a great potential for further advanced PSC technology. Abundant endeavors have been made to design and synthesize new non-fullerene acceptors, since active layer acts an essential role in light harvest and exciton separation.4, 12, 18-20 Nevertheless, interlayer engineering also acts a crucial role in optimizing device performance.21 Usually, the organic semiconductors and metal electrodes are incompatible, which always leads to large contact resistance, energy losses, high energy barrier and increased exciton recombination.22-24 The presence of interlayers can lead to an ohmic contact through the formation of interface dipole, following a positive impact on all the device parameters, e.g., open circuit voltage (Voc),25-26 short-circuit current density (Jsc),21, 27 and fill factor (FF).28 Consequently, interlayers are also necessary for non-fullerene PSCs to achieve better performance. The molecular orbital levels and electron-transporting properties of non-fullerene



materials are different to those of fullerenes such as PC71BM, therefore it is essential to develop novel cathode interfacial materials for non-fullerene PSCs. However, so far little attention has been paid to the cathode interlayers for non-fullerene PSCs, such as ZnO,29-30 polyfluorene derivatives,14,31-32 and perylene-diimide(PDI) derivatives.33-34 Most of them didn’t investigate the influence of the interlayer thickness. A thicker interlayer would be conducive to the large-area device fabrication. What’s more, most of the reported work adopted a stereotyped Al cathode, which was easy to be oxidized. High work function (WF) metal electrodes, for instance, Cu, Ag and Au, would be conducive to the device stability.35-37 In this study, we introduce a small molecule perylene diimide zwitterion (PDI-z) as a cathode interlayer to non-fullerene PSCs. Owing to possessing the extraordinary properties of high electron affinity, easy functionalization, high conductivity and photochemical stability, 38-40 perylene diimide (PDI) was chose as the conjugated core. The self-organized π-stacks in solid make them possess high conductivities to overcome the thickness limitation.41-42 Zwitterion as the side group is inspired by its ability of modifying various metal electrodes, for instance, Al, Cu ,Ag, Au.24, 38 We adopt a donor material (PBDB-T) and a non-fullerene acceptor material (IT-M) as active layer and PDI-z as cathode interlayer to fabricate conventional architecture devices. The non-fullerene devices achieve a promising PCE of 11.23%. At the same time, the PCE values reach above 80% of the optimal value on a large scale of PDI-z thickness (5–40 nm). Moreover, the PDI-z devices also exhibit good performance when high WF metals (for instance, Cu, Ag, and Au) are applied as


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electrodes.

2. EXPERIMENTAL Synthesis of PDI-N Perylene tetracarboxylic dianhydride (1.00 g, 2.50 mmol) was added into a flask. 3-dimethylaminopropylamine (2.60 g, 25.00 mmol) and 40 ml of isobutanol were injected after the flask was evacuated and filled with nitrogen several times. Subsequently, the mixture was heated at 90 oC overnight. Crude product was filtered and further washed with an excess of deionized water and ethanol. The obtained residue was stirred with 200 mL of 10% potassium carbonate solution at 50 oC for 1 h to get rid of the residual PTCDA. The solid product was filtered, and then successfully washed with water and alcohol. 1.26 g red solid product was obtained after drying in the vacuum with an 89.9% yield. 1H NMR (400 MHz, CF3COOD), δ (ppm): 8.59-8.53 (q, J = 8.0 Hz, 8H), 4.25-4.22 (t, J = 8.0 Hz, 4H), 3.19-3.15 (t, J = 8.0 Hz, 4H), 2.86 (s, 12H), 2.23-2.16 (m, 4H).

13

C NMR (100 MHz, CF3COOD), δ

(ppm): 135.84, 132.69, 128.90, 125.93, 123.96, 121.30, 55.79, 42.83, 36.84, 22.77. TOF MS (m/z): [M+H]+ caled for C34H33N4O4 : 561.2502; found: 561.2476. Synthesis of PDI-z PDI-N (100 mg, 0.18 mmol) and 1,3-propanesultone (440 mg, 3.60 mmol) were dissolved in 30 ml of chloroform and methanol (chloroform:methanol = 1:1, v/v). After three days of refluxing, the solvent was removed. The aqueous solution of crude product was added dropwise into stirring ethyl alcohol and the pure product



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was filtered to yield a red solid (90mg, 62.1%).1H NMR (400 MHz, CF3COOD), δ (ppm): 8.62-8.57 (m, 8H), 4.28-4.25 (t, J = 8.0 Hz, 4H), 3.51-3.49 (t, J = 4.0 Hz, 4H), 3.23-3.16 (m, 8H), 3.02 (s, 12H), 2.36-2.24 (m, 8H).

13

C NMR (100 MHz,

CF3COOD), δ (ppm): 135.62, 132.65, 128.92, 125.86, 124.02, 121.56, 69.00, 66.04, 62.65, 62.50 50.57, 43.25, 22.91, 17.90. TOF MS (m/z): [M+2H]2+ caled for C40H46N4O10: 403.1328, found: 403.1355.

3. RESULT AND DISCUSSION The synthesis processes of PDI-z were showed in Scheme 1. PDI-z was simply obtained by two-step reaction. Firstly, PDI-N was synthesized by dehydration reaction with an 89.9% yield. Then, PDI-N was quaternized by 1,3-propanesultone to obtain a zwitterionic compound PDI-z. PDI-z was insoluble in non-polar solvents for instance, dichlorobenzene, chlorobenzene and chloroform, and soluble in polar solvents for instance, 2, 2, 2-trifluoroethanol (TFE), methanol, DMF, DMSO and water, which was very important for multilayer-device fabrication. The molecule structure was identified by NMR and high resolution mass spectra.

Scheme 1. Synthesis processes for PDI-N and PDI-z


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In order to learn about the basic optical property of PDI-z, the ultraviolet-visible (UV-vis) absorption of PDI-z was tested. As it was depicted in Figure 1a, the absorption peaks of PDI-z solution were located at 491 nm and 526 nm, in the meanwhile, the absorption peaks of PDI-z film were located at 493 nm and 564 nm. Owing to strong solid-state packing of PDI core, the absorption of PDI-z thin film displayed a prominent red-shift and a broader range compared to its solution spectrum.43 Cyclic voltammetry was adopted to explore the electrical property of PDI-z (Figure 1b). LUMO level of PDI-z was calculated to be -4.05 eV in terms of the onset reduction potential, which was very close to that of IT-M (-3.98 eV).3 Similar LUMO levels of PDI-z and IT-M made it easy to bridge electrons to transport from IT-M to PDI-z. Based on the onset oxidation potential, the HOMO level was evaluated to be -6.08 eV.

Figure 1. (a) Solution and film absorption spectra of PDI-z. (b) Cyclic voltammogram of PDI-z film. To explore the interfacial modification ability of PDI-z in non-fullerene PSCs, we fabricated the conventional PSC devices possessing the architecture of ITO/PEDOT:PSS/PBDB-T:IT-M/interlayer/Al. Figure 2 showed the device



structure, molecule structures of active layer materials and energy levels of materials. We also prepared the contrastive PSC devices, in which the PFN and PDI-N were employed as interlayers.21, 38 The alcohol could effectively remove residual additives and passive the surface traps in fullerene PSCs to improve device performance.44-45 To rigorously estimate the ability of interfacial modification of PDI-z and exclude the impact of the alcohol solvent, we fabricated non-fullerene PSCs with or without solvent treatment. Figure 3a and Table 1 represented the typical current density–voltage (J–V) curves and device parameters, respectively. Both of the devices with or without TFE treatment displayed poor performance. However, the devices treated by solvent possessed a slightly higher PCE value compared to the devices without solvent treatment. The results indicated that solvent treatment also presented a positive influence on device performance in non-fullerene PSCs. Meanwhile, the devices with cathode interlayers (PFN, PDI-N and PDI-z) exhibited significantly improved performance. The device with PFN as interlayer displayed a Voc of 0.933 V, a Jsc of 16.79 mA cm-2, and a FF of 58.07%, obtaining a middling PCE of 9.10%. The low FF might indicate that PFN was not an ideal interlayer in PBDB-T:IT-M system.46 And under the optimal condition, the device with PDI-N as interlayer also exhibited good performance: a Voc of 0.940 V, a Jsc of 16.09 mA cm-2, a FF of 67.76% and a noticeable PCE of 10.25%. Simultaneously, after PDI-z was deposited onto

active layer, the device displayed prominent performance: an optimal PCE of 11.23%, a Voc of 0.939 V, a Jsc of 16.12 mA cm-2, and an ultrahigh FF of


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74.17%. The Jsc of PDI-z was slightly lower than that of PFN. There might be two reasons for this situation. One was that PFN might enhance light-trapping of active layer by optical spacer effect,47 the other was that the reflected incident light could be absorbed by PDI-z film. The external quantum efficiency (EQE) curves

of the non-fullerene PSC devices based on TFE, PFN and PDI-z were presented in Figure 3b. The EQE value of PDI-z device was little lower than that of PFN device, but higher than that of the TFE treatment devices. The integration Jsc values calculated from EQE curves matched well with the measured values with 5% error. Compared to the control PFN device, the Voc of PDI-z device increased from 0.933 V to 0.939 V and the Jsc reduced from 16.79 mA cm-2 to 16.12 mA cm-2. However, the FF presented a drastically increase from 58.07% to 74.17%, which made a great upgrade on the device efficiency. The outstanding performance indicated that the small molecule PDI-z was an excellent ETL to elevate the PCEs of non-fullerene PSCs.



Figure 2. (a) Device configuration of non-fullerene PSC. (b) Molecule structures of active layer materials. (c) Energy levels of materials.

The impact of interlayer treatment on the Al electrode was also explored by the ultraviolet photoelectron spectroscopy (UPS). Figure. S1a showed WF of bare Al, PFN/Al and PDI-z/Al. After deposition of PFN and PDI-z onto the Al electrodes, the WF values dramatically decreased. For PDI-z, SO3- was close to Al electrode and N+ was far away from Al electrode. Therefore, regular dipole moments were formed at the surface of electrode, which were beneficial to facilitate electron transport and extraction.48 To gain insights into the effect of interlayer on the device parameters from a topographic perspective, the morphologies of the PBDB-T:IT-M film with various treatments were measured using atomic force microscopy (AFM). As it was depicted in Figure


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S2, the root-mean-square (RMS) roughness value of pristine active layer was 2.14 nm. After treated by TFE, the surface morphology of PBDB-T:IT-M film did not represent obvious change with a RMS of 2.11 nm. After PFN and PDI-z were deposited onto active layer, the surfaces were smoother and the RMS values reduced to 1.36 nm and 1.28 nm, respectively, which suggested that PDI-z possessed an approximate ability to spin-coat a uniform film on active layer compared with the polymer PFN. A uniform interlayer film is contributed to fabricate large-area device and slow down metal electrode diffusing to the active layer.49 To explore the impact of interlayers on electron-transporting behaviour, the

electron-only

devices

possessing

the

configuration

of

ITO/ZnO/active-layer/Interlayers/Al were fabricated. The J0.5–V curves were depicted in Figure 3d. The devices with or without solvent treatment possessed low electron mobilities of 3.08×10-6 and 2.56×10-6 cm2V-1s-1, respectively. Nevertheless, electron mobilities of PFN and PDI-z device further heightened to 3.78×10-5 and 4.91×10-5 cm2V-1s-1, respectively, which were over 10 times greater than those of devices without interlayer. It was worth noting that benefitting from the introduction of functional groups (i.e., SO3- and N+), the conductivity of PDI-z was higher than that of PDI-C12, which consisted of PDI unit and alkyl chain. (Figure S5) The high conductivity of PDI-z should be responsible for the higher apparent electron mobility of PDI-z device. We also found that the electron mobility of PDI-z device was higher compared to PFN



device. The higher electron mobility was beneficial to the increased FF. The dark J–V curves of PSC devices had been used to demonstrate the diode-behaviour and sequentially estimate contact resistance and charge recombination, which were presented in Figure 3c. The reverse bias leakage current of the PSC device with PDI-z was greatly suppressed than those of the bare Al and PFN/Al control devices during the voltages from -1.5 V ~ 0 V. The supressed dark current indicated charge recombination was decreased and hole transport was obstructed at the cathode interface, consequently, giving rise to the enhanced FF. In the meanwhile, the n-type nature of PDI core could obstruct the hole injection and make it easy for the electron transport.50


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Figure 3. (a) J–V curves of non-fullerene devices with different interlayers. (b) The corresponding EQE spectra. (c) The corresponding dark J-V curves. (d) The corresponding J0.5–V curves of electron-only devices with various interlayers.

Table 1. Device parameters of the non-fullerene PSC devices with different ETLs.



Voc Interlayer

None

TFE

PFN

PDI-N

PDI-z

a

Jsc

FF 2

PCE

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Rs

Rsh 2

[mA/cm ]

[%]

[%]

0.656

15.36

58.63

5.91a

8.2

484.6

0.657±0.006

15.21±0.20

57.84±0.72

5.78b ± 0.12

8.2±0.6

484.6±20.9

0.715

15.44

60.36

6.67a

10.1

881.7

10.3 ± 0.7

854.4 ± 50.7

13.6

892.9

13.9 ± 0.6

695.6 ± 128.0

6.2

1553.0

7.1 ± 0.7

1450.4 ± 63.6

4.1

1529.4

4.3 ± 0.2

1511.0 ± 31.9

0.707 ± 0.008

15.62 ± 0.38

60.14 ± 0.23

0.933

16.79

58.07

0.932 ± 0.003 0.940 0.941 ± 0.001 0.939 0.938 ± 0.001

16.82 ± 0.18 16.09 16.04 ± 0.03 16.12 16.05 ± 0.11

56.86 ± 0.99

[Ω·cm ]

[Ω·cm2]

[V]

b

6.62 ± 0.14 9.10a b

8.91 ± 0.16

67.76

10.25

67.10 ± 0.60

b

a

10.16 ± 0.07

74.17

11.23

73.98 ± 0.20

b

a

11.11 ± 0.12

Best device PCE. b The average PCE values received from 10 devices.

Thick interlayers played an important role in large-area printing manufacturing. Besides the improved device behaviour, we further studied the impact of interlayer thickness on the behaviour of non-fullerene photovoltaic devices. Usually, the bulk resistance of interlayer would be increased with the thickness, which would obstruct the charge transfer and was harmful to device performance. Because of the p-type backbone of PFN, usually, the electrons were injected into the cathode from active layer through “channel effect”, which allowed the film to remain ultrathin, ~5 nm. The PCE values of PFN device reduced drastically from 9.10% to 1.22% with PFN thickness heightening from 4 nm to 10 nm, and series resistance (Rs) would have a 46-fold increase (see Table S1). This thickness-sensitivity property was an obstacle for PFN to apply in large-area printing manufacturing. Intriguingly, as presented in Figure 4a and Table 2, we could find that the performance of PDI-z PSC was insensitive to the thickness of the PDI-z. For PDI-z, the n-type backbone and strong π-π stacking endowed it with the inherent excellent


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electron transporting property. The PCE values of PDI-z devices could remain over 90% of the optimal PCE value with 10.02% at the thickness of 22 nm, at the same time, over 80% of the optimal value with 9.02% at the thickness of 40 nm. Although the thickness of PDI-z interlayer ranged from 5 nm to 40 nm, the series resistances were elevated only from 4.1 Ω cm2 to 7.6 Ω cm2, which were stable at a low level. Apart from the electronic property, energy level matching was also an important factor in thickness dependence. It was known that the LUMO level of PFN was much higher than that of IT-M. In Figure 2c, with PFN thickness increasing, the electron would not hop to the electrode. However, in the case of PDI-z, electrons could be injected into PDI-z and transport in the PDI-z film because the LUMO level of PDI-z was comparable to that of IT-M. Therefore, when the thickness was increased, the PSC devices with PDI-z interlayer could maintain high PCE values.



Figure 4. (a) J–V curves of the non-fullerene PSC devices with various thicknesses of PDI-z. (b), (c), (d) J–V curves of PDI-z /PFN non-fullerene PSCs with high WF metals as top electrodes.


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Table 2. Device parameters of the PDI-z devices with different PDI-z thicknesses. ETL

Thickness (nm) 5±1

8±2

12 ± 3 PDI-z 16 ± 2

22 ± 3

40 ± 3 a

Jsc

Voc

FF 2

Rs

PCE

Rsh

[V]

[mA/cm ]

[%]

[%]

[Ω·cm ]

[Ω·cm2]

0.917

16.27

66.40

9.91a

7.7

1222.7

8.2 ± 0.8

1249.1 ± 53.8

0.915 ± 0.002

16.17 ± 0.14

66.43 ± 0.88

2

b

9.62 ± 0.17 a

0.939

16.26

73.03

11.15

4.6

485.59

0.939 ± 0.002

15.80 ± 0.29

73.46 ± 0.38

10.96b ± 0.17

5.5 ± 0.9

1411.5 ± 147.7

0.939

16.12

74.17

11.23a

4.1

1529.4

b

0.938 ± 0.001

16.05 ± 0.11

73.98 ± 0.20

11.11 ± 0.12

4.3 ± 0.2

1511.0 ± 31.9

0.936

15.81

73.2

10.83a

4.1

1351.9

4.8 ± 0.5

1355.9 ± 31.9

0.937 ± 0.002

15.78 ± 0.11

72.70 ± 0.48

b

10.47 ± 0.25 a

0.923

15.30

70.96

10.02

6.6

1340.9

0.922 ± 0.004

15.14 ± 0.15

70.87 ± 0.39

9.66b ± 0.26

6.8 ± 0.6

1314.6 ± 76.4

0.900

15.01

66.78

9.02a

7.6

1247.5

8.1 ± 0.6

1250.4 ± 42.4

0.902 ± 0.006

14.98 ± 0.07

66.40 ± 0.33

b

8.73 ± 0.16


Finally, we also used high WF metals (Au, Ag, Cu) to displace Al as the top cathodes. Figure S1b depicted the UPS spectra of various metal electrodes (Au, Ag, Cu) treated by PDI-z. After modification with a paper-thin PDI-z film (~ 5 nm), the WF of Au, Ag and Cu was pained at – 4.7 eV, -4.3 eV, - 4.5 eV. The result suggested that PDI-z possessed the ability of modifying high WF metals, which indicated the devices employed PDI-z as cathode interlayer and high WF metals as electrodes might show a good performance. The J-V curves of PBDB-T:IT-M devices with high WF metals as electrodes were provided in Figure 4b, 4c, 4d and all the device data was summarized in Table 3. Compared to PFN devices, all PDI-z devices displayed better performance with the PCEs over 8%. Specially, with Ag as electrode, a high PCE 9.38% was obtained with a Voc of 0.914 V, a Jsc of 15.49 mA cm-2, and a FF of 66.29%. With Ag and Au as electrodes, the Voc and Jsc values of PDI-z devices were very close to those of



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PFN based devices (0.914 V Vs 0.897 V, 0.890 V Vs 0.893 V and 15.49 mA cm-2 Vs 15.62 mA cm-2, 15.24 mA cm-2 Vs 15.27 mA cm-2), however, the FF values were markedly different (66.29% Vs 61.33% and 62.26% Vs 50.61%), which made the PDI-z based devices better performance. With Cu as electrode, Jsc value of PDI-z device was approximate to that of PFN device (15.47 mA cm-2 Vs 15.44 mA cm-2), nevertheless, both the Voc and FF values of PDI-z devices were higher than those of PFN devices (0.871 V Vs 0.679 V and 61.28% Vs 53.22%). The higher FF values induced the excellent performance of PDI-z devices with high WF metal electrodes, indicating that the broad application of PDI-z in non-fullerene PSC devices. Table 3. Device parameters of the PDI-z devices based on PBDB-T:IT-M with high WF metals as top electrodes. Cathode PFN/Ag

PDI-z/Ag

PFN/Au

PDI-z/Au

PFN/Cu

PDI-z/Cu

a

Voc

Jsc

FF

PCE

Rs

Rsh

[V]

[mA/cm ]

[%]

[%]

[Ω·cm ]

[Ω·cm2]

0.897

15.62

61.33

8.60a

8.5

1074.6

10.6 ± 1.5

944.6 ± 104.5

6.0

982.1

7.2 ± 1.2

1075.4 ± 55.4

0.897 ± 0.002 0.914 0.909 ± 0.004

2

15.62 ± 0.23 15.49 15.64 ± 0.26

58.72 ± 1.89 66.29 63.67 ± 1.02

b

8.32 ± 0.23 9.38

a

b

9.17 ± 0.18 a

2

0.893

15.27

50.61

6.90

8.5

437.8

0.893 ± 0.004

14.91 ± 0.21

49.80 ± 0.75

6.73b ± 0.26

8.0 ± 0.9

465.9 ± 56.0

0.890

15.24

62.26

8.45a

8.1

1032.7

b

0.889 ± 0.002

14.73 ± 0.54

61.25 ± 1.02

8.26 ± 0.20

9.1 ± 1.18

1042.3 ± 99.9

0.679

15.44

53.22

5.58a

10.4

312.1

10.3 ± 0.4

341.2 ± 23.8

0.682 ± 0.011

15.50 ± 0.56

53.05 ± 0.89

b

5.61 ± 0.28 a

0.871

15.47

61.28

8.26

0.868 ± 0.006

15.00 ± 0.28

61.62 ± 0.49

8.08b ± 0.14

9.4

915.8

8.2 ± 0.8

958.2 ± 46.4



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4. CONCLUSIONS A water/alcohol-soluble zwitterion PDI-z was synthesized and applied as ETL for non-fullerene PSCs. Its easy accessibility, high conductivity, suitable energy level and good ability of modifying high WF metals made it a hopeful interlayer material. A prominent PCE value (11.23%) was obtained with an ultrahigh FF of 74.17% for PBDB-T:IT-M devices. Moreover, the PDI-z non-fullerene PSCs displayed an excellent performance over a wide range (5 nm – 40 nm) of interlayer thickness. The ability of modifying high WF metals (e.g., Au, Ag, Cu) promoted its potential in long-stable non-fullerene PSCs. Nowadays non-fullerene PSCs achieving high

efficiency over 10% seems easily, the breakthrough

in large-area

print-processing and stability will accelerate their commercial application. Our results suggest that PDI-z could become a well alternative cathode interlayer for future non-fullerene PSCs.

ASSOCIATED CONTENT Supporting Information Experiment details, consisting of measurement and characterization, materials and device fabrication; device parameters of PFN devices; UPS spectra of various electrodes; AFM height images; stability of devices; absorption spectra; I−V curves for electron-only transfer devices and electron paramagnetic resonance (EPR) spectra.



Page 20 of 28

AUTHOR INFORMATION Corresponding Authors *E-mail: [email protected] *E-mail: [email protected]. Notes The authors declare no competing financial interest.

ACKNOWLEDGEMENTS This research was supported by Zhejiang Provincial Natural Science Foundation of China (LY18E030012), National Natural Science Foundation of China (No. 51603213, 51773213 and 61474125), the Key Research Program of Frontier Sciences (QYZDB-SSW-JSC047), (2018C01047),

and

Zhejiang

Ningbo

Province

Natural

Science

Science

and

Technology

Foundation

of

Plan

China

(2017A610016, 2017A610017 and 2017A610014). The authors also thank Mrs. Man Liu for the high-resolution mass spectrum experiments.

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TOC Graphic:


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Perylene Diimide-Based Zwitterion as the Cathode Interlayer for High

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