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. 2018 Aug 31:6:128-137.
doi: 10.1016/j.isci.2018.07.016. Epub 2018 Jul 24.

High-Energy-Level Blue Phosphor for Solution-Processed White Organic Light-Emitting Diodes with Efficiency Comparable to Fluorescent Tubes

Shumeng Wang  1 , Lei Zhao  1 , Baohua Zhang  2 , Junqiao Ding  3 , Zhiyuan Xie  4 , Lixiang Wang  4 , Wai-Yeung Wong  5
Affiliations

High-Energy-Level Blue Phosphor for Solution-Processed White Organic Light-Emitting Diodes with Efficiency Comparable to Fluorescent Tubes

Shumeng Wang et al. iScience. .

Abstract

A high-energy-level blue phosphor FIr-p-OC8 has been developed for solution-processed white organic light-emitting diodes (WOLEDs) with comparable fluorescent tube efficiency. Benefiting from the electron-donating nature of the introduced alkoxy, FIr-p-OC8 shows not only efficient blue light but also elevated highest occupied molecular orbital/lowest unoccupied molecular orbital levels to well match the dendritic host H2. Consequently, the hole scattering between FIr-p-OC8 and H2 can be prevented to favor the direct exciton formation on the blue phosphor, leading to reduced driving voltage and thus improved power efficiency. By exploiting this approach, a maximum power efficiency of 68.5 lm W-1 is achieved for FIr-p-OC8-based white devices, slightly declining to 47.0 lm W-1 at a practical luminance of 1,000 cd m-2. This efficiency can be further raised to 96.3 lm W-1 @ 1,000 cd m-2 when a half-sphere is applied to increase light out-coupling. We believe that our results can compete with commercial fluorescent tubes, representing an important progress in solution-processed WOLEDs.

Keywords: Inorganic Materials; Optoelectronics; Organometallic Chemistry.

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Figures

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Graphical abstract
Figure 1
Figure 1
Design of High-Energy-Level Blue Phosphors (A) Molecular structures of blue phosphors (FIrpic, FIr-m-OC8 and FIr-p-OC8). (B) UV-Vis absorption spectra in dichloromethane (DCM) together with photoluminescent (PL) spectra in toluene (The black circles and arrows indicate the corrsponding vertical axis for each data curves). (C) PL decay curves in toluene. (D) Cyclic voltammograms in solution using 0.1M n-Bu4NClO4 as supporting electrolyte at a scan rate of 100 mV s−1. (E) HOMO/LUMO level alignment of the blue phosphors. Also see Scheme S1 and Figure S1.
Figure 2
Figure 2
Performance Comparison between FIrpic- and FIr-p-OC8-Based Blue Devices with the Same Doping Concentration (15 wt. %) (A) Current density-voltage-luminance characteristics (The black circles and arrows indicate the corrsponding vertical axis for each data curves). (B) Power efficiency-luminance characteristics. Also see Figures S5 and S6, and Table S2.
Figure 3
Figure 3
Analysis of the Hole Scattering-Induced Influence (A) Working mechanism of FIrpic-based blue device. (B) Current density-voltage characteristics of FIrpic-based hole-only devices with different doping concentration of 0, 1, 5, and 15 wt.%. (C) Transient EL decay curves for FIrpic-based blue device with a doping concentration of 15 wt. %. (D) Working mechanism of FIr-p-OC8-based blue device. (E) Current density-voltage characteristics of FIr-p-OC8-based hole-only devices with different doping concentration of 0, 1, 5, and 15 wt.%. (F) Transient EL decay curves for FIr-p-OC8-based blue device with a doping concentration of 15 wt.%. Also see Figure S4 and Table S1.
Figure 4
Figure 4
Performance of FIr-p-OC8-Based Blue and White Devices with an EML Composed of H2, 25 wt.%; FIr-p-OC8, x wt.% Ir(Flpy-CF3)3 (A–C) EL spectra at 1,000 cd m−2; current density-voltage-luminance characteristics; and power efficiency as a function of luminance for devices without out-coupling (The black circles and arrows indicate the corrsponding vertical axis for each data curves). (D–F) EL spectra at 1,000 cd m−2; current density-voltage-luminance characteristics; and power efficiency as a function of luminance for devices with light out-coupling (The black circles and arrows indicate the corrsponding vertical axis for each data curves). Also see Figures S5 and S7–S15, and Tables S3 and S4.
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