Green-synthesized, low-cost tetracyanodiazafluorene (TCAF) as electron injection material for organic light-emitting diodes

Citation: Yang Bing, Zhao Jianfeng, Wang Zepeng, Yang Zhenlin, Lin Zongqiong, Zhang Yanni, Li Jiewei, Xie Linghai, An Zhongfu, Zhang Hongmei, Weng Jiena, Huang Wei. Green-synthesized, low-cost tetracyanodiazafluorene (TCAF) as electron injection material for organic light-emitting diodes[J]. Chinese Chemical Letters, 2019, 30(11): 1969-1973. doi: 10.1016/j.cclet.2019.08.054 shu

Green-synthesized, low-cost tetracyanodiazafluorene (TCAF) as electron injection material for organic light-emitting diodes

English

Green-synthesized, low-cost tetracyanodiazafluorene (TCAF) as electron injection material for organic light-emitting diodes

a.
Key Laboratory of Flexible Electronics(KLOFE) & Institute of Advanced Materials(IAM), Jiangsu National Synergetic Innovation Center for Advanced Materials(SICAM), Nanjing Tech University(Nanjing Tech), Nanjing 211816, China
b.
Key Laboratory for Organic Electronics & Information Displays(KLOEID) and Institute of Advanced Materials, Nanjing University of Posts & Telecommunications, Nanjing 210023, China
c.
Shaanxi Institute of Flexible Electronics(SIFE), Northwestern Polytechnical University(NPU), Xi'an 710072, China
^*Corresponding authors.
^** Corresponding author at: Key Laboratory of Flexible Electronics (KLOFE) & Institute of Advanced Materials (IAM)
Jiangsu National Synergetic Innovation Center for Advanced Materials (SICAM)
Nanjing Tech University (Nanjing Tech)
Nanjing 211816
China.
E-mail addresses: iamjfzhao@outlook.com (J. Zhao)
iamhmzhang@njupt.edu.cn (H. Zhang)
iamjnweng@nwpu.edu.cn (J. Weng)
iamwhuang@njtech.edu.cn (W. Huang).
¹ These two authors contributed equally to this work.
Received Date: 05 June 2019
Accepted Date: 29 August 2019
Revised Date: 29 July 2019
Available Online: 22 November 2019

Abstract: Two electron-deficient azaacenes including di- and tetra-cyanodiazafluorene (DCAF and TCAF) with the advantages of deep lowest unoccupied molecular orbital (LUMO), green-synthesis, low-cost, simply purification method, excellent yields have been obtained, characterized and used as electron injection materials (EIMs) in three groups of electroluminescence devices. Device B with TCAF as EIM exhibited the best performance including turn-on voltage of 5.0 V, stronger maximum luminance intensity of 31, 549 cd/m², higher luminance efficiency of 62.34 cd/A and larger power efficiency of 21.74 lm/W which are 0.53, 6.7, 9.3 and 15.3 times than that of device A with DCAF as EIMs, respectively. The enhanced interfacial electron injection ability of TCAF than that of DCAF is supported by its better electron mobility in electron-only device, deeper LUMO (-4.52 eV), and stronger electronic affinity. Best external quantum efficiency of 16.56% was achieved with optimized thicknesses of TCAF as EIM and TPBi as electron transporting layer. As a new comer of acceptor family, TCAF would push forward organic electronics with more fascinating and significant applications.

Key words:

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Scheme 1 (a) The synthetic routes of DCAF and TCAF: (ⅰ) 1H-indene-1, 2, 3-trione, 2, 3-diaminomaleonitrile (DAMN), EtOH, refluxed, 10 h, 85.0% for DCAF; (ⅱ) DCAF, malononitrile, EtOH, refluxed, 10 h, 91.5% for TCAF; (ⅲ) 1, 2, 3-indantrione, DAMN, and EtOH, refluxed, 10 h; then malononitrile, refluxed, another 10 h. Packing modes of DCAF (b, d) and TCAF (c, e) in single crystals.

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Figure 1 (a) Cyclic voltammogram recorded for DCAF and TCAF; b) Wave functions for the HOMO and LUMO of DCAF and TCAF molecules, respectively; (c, d) Calculated electrostatic potentials of single molecule of DCAF and TCAF.

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Figure 2 (a) Schematic configuration of devices A and B; (b) Energy level diagrams of devices A and B; (c) molecule structures of organic materials in devices A and B; (d) J–V–L characteristics of devices A and B; (e) LE–L characteristics of devices A and B; (f) PE–L characteristics of devices A and B; (g) L–V characteristics of DCAF/TCAF-based electrononly devices C and D.

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Figure 3 The (a) J–V–L characteristics of devices B, E, and F; (b) LE–L characteristics of devices B, E, and F; (c) PE–L characteristics of devices B, E, and F. ^* Means the curves of device B were presented for comparison.

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Figure 4 The (a) J–V–L characteristics of devices G, B, H and I; (b) LE-L characteristics of devices G, B, H, and I; (c) PE–L characteristics of devices G, B, H and I. ^*Means the curves of device B were presented for comparison.

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Table 1. Electrochemical and thermal characteristics of DCAF and TCAF.

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Table 2. Three groups of device characteristics: Ⅰ. Devices A and B with different CAFs as EIM; Ⅱ. Devices B, E, and F with different thicknesses of TCAF; Ⅲ. Devices G, B, H and I with different thicknesses of TPBi (30, 40, 50, and 60 nm).

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