High‐Performance Narrowband OLED with Low Efficiency Roll‐Off Based on Sulfur‐Incorporated Organoboron Emitter

Abstract

Multi‐resonance (MR) based organoboron emitters exhibiting high‐efficiency narrowband thermally activated delayed fluorescence (TADF) have become a critical material component for constructing high‐performance organic light‐emitting diodes (OLEDs) with high color purity and high color gamut. However, most of the MR‐TADF devices suffer from severe efficiency roll‐off at high current density due to the relatively large singlet–triplet splitting energy, long excited state lifetime, and slow reverse intersystem crossing rate (k RISC). Herein, by utilizing a sulfur atom‐fused donor unit, 7H‐benzo[4,5]thieno[2,3‐b]carbazole, an organic boron emitter (BTC‐BNCz) capable of high efficiency and low efficiency roll‐off narrowband TADF emission is developed. Benefitting from the heavy atom effect of the sulfur atom, kRISC up to 1.6 × 105 s−1 is achieved, which could greatly reduce the undesired quenching effect. Consequently, the OLED using BTC‐BNCz as dopant exhibits high external quantum efficiency (EQE) of 27.0% with full width at half maximum (FWHM) of 35 nm. Moreover, by utilizing a TADF material with a high horizontal dipole ratio as assistant host, outstanding device performance is achieved with a maximum EQE of 35.2% and FWHM of 37 nm, featuring slow efficiency roll‐off.

Peripheral halogen atoms in multi-resonant thermally activated delayed fluorescence emitters: the role of heavy atoms in intermolecular interactions and spin orbit coupling

“…Additional examples of HAE investigations for MR-TADF emitters are included in the ESI,† although we note that in all cases these involve heavy atom substitution directly within the MR-TADF core. 35–47…”

Efficient narrowband bluish-green emitters derived from a double-carbazole-fused organoboron multiple resonance skeleton with internal-structure modification

“…The thiophene group was selected as the embedded unit between pyrrole and benzene rings, as it is an aromatic and rigid group with cyclic delocalized π-orbitals, 2,35 which allows for further π-orbital extension of the CzBN skeleton. 36,37 Theoretical calculations reveal that the embedded thiophene units in both emitters sufficiently contribute to their MR distributions, thereby narrowing their energy gaps without harming their narrowband features. 38 As a result, BTPCzBN and BTPBN both exhibit similar bathochromic narrowband bluish-green emissions in dilute solution, with small FWHMs of 23 and 25 nm, respectively.…”

Reducing intersystem crossing rates of boron emitters for high-efficiency and long-lifetime deep-blue OLEDs

“…Boron-based blue emitters have gained significant attention due to their narrow emission bandwidth, making them attractive for high color purity OLEDs. 38–50 While the research studies on boron emitters have mainly focused on the promotion of device efficiency through the TADF characteristics, the development of boron-based emitters for F-OLEDs is extremely scare. 51–54 Currently, it remains unclear what kind of organic blue emitters can simultaneously achieve high efficiency, high color purity and long operational lifetime in F-OLEDs.…”