High Triplet Energy Level Achieved by Tuning the Arrangement of Building Blocks in Phosphorescent Polymer Backbones for Furnishing High Electroluminescent Performances in Both Blue and White Organic Light-Emitting Devices

Abstract

A high triplet energy level (E) of ca. 2.83 eV has been achieved in a novel polymer backbone through tuning the arrangement of two kinds of building blocks, showing enhanced hole injection/transporting capacity. Based on this new polymer backbone with high E, both blue and white phosphorescent polymers were successfully developed with a trade-off between high E and enhanced charge-carrier transporting ability. In addition, their photophysical features, electrochemical behaviors, and electroluminescent (EL) properties have been characterized in detail. Benefitting from the advantages associated with the novel polymer backbone, the blue phosphorescent polymers show top-ranking EL performances with a maximum luminance efficiency (η) of 15.22 cd A, corresponding to a power efficiency (η) of 12.64 lm W, and external quantum efficiency (η) of 6.22% and the stable Commission Internationale de L'Eclairage (CIE) coordinates of (0.19, 0.38). Furthermore, blue-orange (B-O) complementary-colored white phosphorescent polymers based on this novel polymer backbone were also obtained showing encouraging EL efficiencies of 12.34 cd A, 9.59 lm W, and 4.10% in the optimized WOLED together with exceptionally stable CIE coordinates of (Δx = 0.014, Δy = 0.010) in a wide driving voltage range from 4 to 16 V. All of these attractive EL results achieved by these novel phosphorescent polymers show the great potential of this new polymer backbone in developing highly efficient phosphorescent polymers.

Single White‐Emitting Polymers with High Efficiency, Low Roll‐Off, and Enhanced Device Stability by Using Through‐Space Charge Transfer Polymer with Blue Delayed Fluorescence as Host for Yellow Phosphor

“…For example, P‐Ir6 remains high LEs of 51.6 and 50.9 cd A −1 at the luminance of 500 and 1000 cd m −2 , respectively, making it the most efficient white‐emitting polymers at such luminances. [ 4–7,9,18–20 ] The corresponding efficiency roll‐off values relative to the maximum value is only 0.6% and 1.9% at 500 and 1000 cd m −2 , respectively ( Figure a), which are significantly lower than previously reported white‐emitting polymers ( Table 2 ). To gain insight into the origin of the small efficiency roll‐off, we fabricate two control devices using Ctrl‐P‐Ir6 and the blend of Ctrl‐P‐Ir6 and P‐TRZ (see Figure 5c for structure) with the same mole ratio as P‐Ir6 (5 mol% for triazine unit) as the emissive layer.…”

“…The second kind is phosphorescent SWPs consisting of metal complex phosphors that can harness triplet excitons via spin–orbital coupling, which are able to achieve 100% IQEs by proper selection of phosphors and polymer hosts with matched energy levels. [ 9–11,18–22 ] Recently, a new kind of SWPs based on thermally activated delayed fluorescence (TADF) [ 23–36 ] emitters, which utilizes the twisted donor–acceptor structure with reduced singlet‐triplet energy splitting (∆ E ST ) to upconvert triplet excitons to singlet ones via reverse intersystem crossing (RISC), has been reported, [ 4–7 ] providing an alternative approach to realize 100% IQEs for SWPs. However, up to now, device performance of SWPs is still behind the requirement of practical application.…”

“…By tuning phosphor content in the polymer to realize partial energy transfer from host to phosphor, simultaneous blue delayed fluorescence and yellow phosphorescence can be generated for white emission. The resulting polymer with 0.6 mol% phosphor exhibits white electroluminescence with Commission Internationale de L'Eclairage (CIE) coordinates of (0.38, 0.43), together with the state‐of‐the‐art luminance efficiency of 50.9 cd A −1 at 1000 cd m −2 , [ 4–7,9,18–20 ] corresponding to a very small roll‐off of 1.9% relative to the maximum efficiency. Moreover, the polymer shows a tenfold increase in device lifetime over the control polymers based on conventional polymer host consisting of only acridan units.…”

Realization of high-power-efficiency white electroluminescence from a single polymer by energy-level engineering

“…Since the first report of SWPs with individual blue and yellow fluorescence emission in 2004,21 a number of SWPs containing two22–27 or three colors28–32 have been reported. Particularly, incorporating phosphorescent emitters to harvest triplet excitons has been an important advance in boosting the device efficiency.…”

Rational Design of π-Conjugated Tricoordinated Organoboron Derivatives With Thermally Activated Delayed Fluorescent Properties for Application in Organic Light-Emitting Diodes

“…Organic light-emitting diodes (OLEDs) have drawn considerable attention for applications in displaying and lighting fields owing to their outstanding advantages nowadays (Choy et al, 2014;Zhang et al, 2015;Im et al, 2017a;Liu et al, 2017bLiu et al, , 2018Pal et al, 2018;Zhu et al, 2018). Unfortunately, their commercialization applications are still limited by the low device performance at high luminance and low external quantum efficiency (EQE) of the emitters.…”