Efficient, narrow-band, and stable electroluminescence from organoboron-nitrogen-carbonyl emitter

Abstract

Organic light-emitting diodes (OLEDs) exploiting simple binary emissive layers (EMLs) blending only emitters and hosts have natural advantages in low-cost commercialization. However, previously reported OLEDs based on binary EMLs hardly simultaneously achieved desired comprehensive performances, e.g., high efficiency, low efficiency roll-off, narrow emission bands, and high operation stability. Here, we report a molecular-design strategy. Such a strategy leads to a fast reverse intersystem crossing rate in our designed emitter h-BNCO-1 of 1.79×10⁵ s^-1. An OLED exploiting a binary EML with h-BNCO-1 achieves ultrapure emission, a maximum external quantum efficiency of over 40% and a mild roll-off of 14% at 1000 cd·m^-2. Moreover, h-BNCO-1 also exhibits promising operational stability in an alternative OLED exploiting a compact binary EML (the lifetime reaching 95% of the initial luminance at 1000 cd m^-2 is ~ 137 h). Here, our work has thus provided a molecular-design strategy for OLEDs with promising comprehensive performance.

Fig. 1. Chemical structures and theoretical calculation results of h-BNCO-1, BNCZ, and BNBNB.

a Chemical structures of h-BNCO-1, BNCZ, and BNBNB. b Optimized geometry structures of their ground (S₀) states via the ωB97XD functional with the nonempirically tuned ω value. c Calculated excited-state energies and spin–orbit couplings via the high-level STEOM-DLPNO-CCSD method. The estimated k_RISC rates are also shown (for details, see the computational details section). d Calculated difference-density plots of the S₁, T₁, and T₂ excited states via the high-level STEOM-DLPNO-CCSD method.

Fig. 2. Photophysical properties of h-BNCO-1.

a UV‒vis absorption and emission spectra of h-BNCO-1 in toluene (1 × 10⁻⁵ M) at room temperature. b Transient PL decays of 1 wt% h-BNCO-1 doped in mCBP films at room temperature (Ф_PL: PLQY; Ф_p: prompt fluorescence quantum efficiency; Ф_d: delayed fluorescence quantum efficiency; τ_p: prompt lifetime; τ_d: delayed lifetime; k_r^s: radiation rate of singlets; k_ISC: intersystem crossing rate; k_RISC: reverse intersystem crossing rate).

Fig. 3. Optimized EL performances of BNCZ- and h-BNCO-1-based OLEDs.

a Device structures with ionization potential and electron affinity (in eV) for each material (HTL hole-transporting layer, EML emitting layer, ETL electron-transporting layer), and the relevant chemical structures of the materials used in the EMLs. b Normalized EL spectra. c EQE−luminance characteristics and efficiency roll-offs of the OLEDs, in which the black dashed line marks the luminance of 1000 cd m⁻², and the green and blue marks represent the device roll-off results at 1000 cd m⁻² of the devices based on h-BNCO-1 and BNCZ, respectively.

Fig. 4. Operational stability of the h-BNCO-1-based OLED.

a The relative luminance versus operating time characteristics at an initial luminance of 1000 cd m⁻². b A summary of the operational lifetime (LT₉₅ at an initial brightness of 1000 cd m⁻²)-wavelength peak-CIE-y coordinate of the reported MR-OLEDs based on binary-EMLs.