A Novel Bridge‐Ring Phosphine Oxide Host 5,10‐[1,2]Benzenophosphanthrene 5,10‐Dioxide for Ultralow‐Voltage‐Driven Blue Thermally Activated Delayed Fluorescence Diodes

Abstract

The molecular configuration optimization is crucial for accurately controlling the intermolecular interactions of organic conjugates. Herein, with the purpose to integrate spherical geometry and optoelectronic properties, the first phosphine oxide (PO) bridge‐ring host 5,10‐[1,2]benzenophosphanthrene 5,10‐dioxide (BPAO2) with phosphorus as bridgehead atom is demonstrated. The sphere‐like paddle‐wheel configuration of BPAO2 gives rise to the highly ordered layer‐by‐layer packing mode, owing to its single molecular orientation, which provides the weak π–π interactions in each layer and hydrogen bond networks between layers. These limited but sufficient interactions are preserved in dilute solution and vacuum‐evaporated film, balancing the charge transportation and the quenching suppression. As consequence, its blue thermally activated delayed fluorescence (TADF) diodes achieve the record‐low turn‐on voltage as 2.3 V, which is remarkably below blue photon energy (≈2.6 eV), and the power efficiency up to ≈70 lm W−1. This work demonstrates the great potential of hetero bridge‐ring systems for optoelectronic applications.

Achieving Balanced Electrical Performance of Host Material through Dual N–P═O Resonance Linkage for Efficient Electroluminescence

“…On account of the dynamically optimal electrical performance for achieving excellent bipolar charge transporting attributes at high E T , blue TADF OLEDs hosted by PADPO were fabricated using a typical structure of ITO/MoO 3 (6 nm)/4,4′-bis-[ N -(1-naphthyl)- N -phenylamino]­biphenyl (70 nm)/ N , N -dicarbazolyl-3,5-benzene ( m CP) (5 nm)/emitting layer (20 nm)/bis­[2-(diphenylphosphino)­phenyl] ether oxide (5 nm)/4,7-diphenyl-1,10-phenanthroline (Bphen) (35 nm)/LiF (1 nm)/Al (100 nm). − In this device, DMAC-DPS was used as a blue TADF emitter. Only pure sky-blue EL with an emission peak at 468 nm and Commission Internationale de l’Eclairage (CIE) coordinates of (0.18, 0.26) that thoroughly originated from DMAC-DPS were captured, which confirms the effective energy transfer from PADPO to the TADF emitter (the inset of Figure b).…”

Recent endeavors and perspectives in developing solution-processable host materials for thermally activated delayed fluorescence organic light-emitting diodes

“…Moreover, the host material can enhance the photoluminescence quantum yield (PLQY) and reduce the delayed lifetime (t d ) of the emissive material, which are essential for improving the device's performance. [68][69][70] Nonetheless, the host material must possess certain characteristics such as adequate spectral overlap (between the emission spectrum of the host and the absorption spectrum of the dopant) to efficiently transfer energy, a high triplet energy (E T ) to prevent back energy transfer from the host to the emitter, and suitable highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels for efficient charge injection and transport. The host materials should also have high thermal stability, including a high glass transition temperature (T g ), to enable the formation of homogeneous and smooth films.…”

Weaving host matrices with intermolecular hydrogen bonds for high-efficiency white thermally activated delayed fluorescence

“…In our previous works, compared to too strong π-π stacking, intermolecular hydrogen bond (IHB) networks in host matrixes were more effective to separate dopants and avoid worsening host-host and host-dopant quenching. [53][54][55][56] It is also noted that IHB modes directly influenced electroluminescence (EL) performance of the devices, which actually provides a desired platform to get a deep insight into the accurate relationship between the regularity of host grids and exciton-involved PL and EL processes in single-layer white TADF systems.…”