Dense Local Triplet States and Steric Shielding of a Multi‐Resonance TADF Emitter Enable High‐Performance Deep‐Blue OLEDs

Abstract

Multi‐resonance thermally activated delayed fluorescence (MR‐TADF) molecules based on boron and nitrogen atoms are emerging as next‐generation blue emitters for organic light‐emitting diodes (OLEDs) due to their narrow emission spectra and triplet harvesting properties. However, intermolecular aggregation stemming from the planar structure of typical MR‐TADF molecules that leads to concentration quenching and broadened spectra limits the utilization of the full potential of MR‐TADF emitters. Herein, a deep‐blue MR‐TADF emitter, pBP‐DABNA‐Me, is developed to suppress intermolecular interactions effectively. Furthermore, photophysical investigation and theoretical calculations reveal that adding biphenyl moieties to the core body creates dense local triplet states in the vicinity of S1 and T1 energetically, letting the emitter harvest excitons efficiently. OLEDs based on pBP‐DABNA‐Me show a high external quantum efficiency (EQE) of 23.4% and a pure‐blue emission with a Commission Internationale de L'Eclairage (CIE) coordinate of (0.132, 0.092), which are maintained even at a high doping concentration of 100 wt%. Furthermore, by incorporating a conventional TADF sensitizer, deep‐blue OLEDs with a CIE value of (0.133, 0.109) and an extremely high EQE of 30.1% are realized. These findings provide insight into design strategies for developing efficient deep‐blue MR‐TADF emitters with fast triplet upconversion and suppressed self‐aggregation.

YCl3-substituted CsPbI3 Perovskite Nanorods for Efficient Red Light-emitting Diodes

“…The orientation of optical TDMs of the unsubstituted and YCl3-substituted CsPbI3 NCs was measured by the ratio of horizontal TDMs (Θ). The experimental data are fitted to the pattern simulated employing the classical dipole radiation model [31][32][33][34]. We confirmed that the Θ values of CsPbI3 NCs and YCl3:CsPbI3 NRs film are determined to be 67% and 75% (Figure 6a-b).…”

High-efficiency and stable short-delayed fluorescence emitters with hybrid long- and short-range charge-transfer excitations

“…Firstly, a moderate dihedral angle between the donor and MR acceptor segments is necessary to guarantee HOMO extension to the bridge-phenyl rings. Secondly, the LE triplet states of the donor and MR acceptor should be energetically close to or higher than CT states to avoid its influence on Δ E ST s 32 . Thirdly, proper substitutions on MR-acceptors should be considered to enhance the MR characters to guarantee the SR-CT excitations on the bridge-phenyl rings.…”

Incorporation of a Boron–Nitrogen Covalent Bond Improves the Charge-Transport and Charge-Transfer Characteristics of Organoboron Small-Molecule Acceptors for Organic Solar Cells

“…Organoboron provides a new idea to design optoelectronic materials [ 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 ]. However, the development of n-type organoboron small-molecular acceptors (OSMAs) with advantages of facile synthesis, synthetic versatility, and simplified purification lags far behind that of their polymer counterparts [ 23 , 24 ].…”