Discrete Mononuclear Platinum(II) Complexes Realize High‐Performance Red Phosphorescent OLEDs with EQEs of up to 31.8% and Superb Device Stability

Abstract

Designing mononuclear platinum(II) complexes that do not rely on intermolecular aggregation for high‐performance red organic light‐emitting diodes remains a formidable challenge. In this work, three robust red‐emitting Pt(II) complexes are created by utilizing a rigid 4‐coordination configuration, where the ligands are formed by linking electron‐donor of triphenylamine (TPA) moieties with electron‐acceptor of pyridine, isoquinoline, and/or δ‐carboline units. The thermal stability, electrochemical, and photophysical properties of the complexes are thoroughly examined. The complexes display efficient red phosphorescence, with high photoluminescence quantum yields and short excited lifetimes. The OLEDs dope with these complexes exhibit high maximum external quantum efficiencies (EQEs) of up to 31.8% with minimal efficiency roll‐off even at high brightness. Significantly, the devices demonstrate exceptional long operational lifetime, with a T90 lifetime of over 14000 h at initial luminance of 1000 cd m−2, indicating the potential for these complexes to be practically utilizes.

Highly efficient platinum(ii) complexes overcoming Pt–Pt interactions and their applications in organic light-emitting diodes

“…And, the absorption peaks at longer wavelengths of 350–430 nm can be attributed to the metal-to-ligand charge transfer (MLCT) transition involving both the benzimidazole ligands and the Pt( ii ) ions. 7,39,40 The photoluminescence (PL) properties of the compounds were examined in DCM solutions with a concentration of 1 × 10 −5 mol L −1 , 1 wt% PMMA films and pure films, all exhibiting green emissions. Double-emission peaks of the complexes are assigned to their monomer emission.…”

“…Phosphorescent emitters, particularly Pt( ii ) complexes, offer advantages such as notably extended emission lifetimes, larger Stokes shifts, facile adjustment of emission colors, and high electrochemical and photostability. 1–12 Over recent decades, phosphorescent organic light-emitting devices (PhOLEDs) have gained widespread utilization in full-color displays due to their ability to harness both singlet and triplet excitons. 1,7,10,12–19 However, a notable challenge arises with Pt( ii ) complexes when integrated into solid-state films, attributed to undesired spectral alterations resulting from robust Pt–Pt interactions induced by the parallel alignment of Pt( ii ) complexes.…”

“…1–12 Over recent decades, phosphorescent organic light-emitting devices (PhOLEDs) have gained widespread utilization in full-color displays due to their ability to harness both singlet and triplet excitons. 1,7,10,12–19 However, a notable challenge arises with Pt( ii ) complexes when integrated into solid-state films, attributed to undesired spectral alterations resulting from robust Pt–Pt interactions induced by the parallel alignment of Pt( ii ) complexes. 4,20–23 This phenomenon leads to broadened and red-shifted emission spectra, ultimately compromising the luminescence performance within solid films.…”

Phenylbenzothiazole-Based Platinum(II) and Diplatinum(II) and (III) Complexes with Pyrazolate Groups: Optical Properties and Photocatalysis

“…These interactions are accompanied by simultaneous changes in the spectroscopic and optical properties, such as assembly-induced metal–metal–to ligand charge-transfer (MMLCT) transitions, which appear at lower energies than the corresponding monomers, and may be utilized to achieve single-doped white OLEDs 3 or stimuli-responsive functional materials. 4 Many of these systems have demonstrated to be solid-state low-red or near-infrared (NIR) emitters, with attractive applications in OLEDs 5 or biological imaging. 6 …”

Deep-Red Organic Light-Emitting Diodes with Increased External Quantum Efficiency and Extended Operational Lifetime by Managing the Composition of Mixed Cohosts

“…When the emission wavelength is extended to the near-infrared (NIR) region (700–1400 nm), light can easily transmit in the human body, and thus, the strong demand for invisible sensing in phototherapy or healthcare equipment has stimulated the development of NIR materials. − Organic light-emitting diodes (OLEDs) possess many intrinsic advantages of ultralight weight, flexibility, and low cost; they are considered potential alternative of LEDs . Despite having obtained considerable values for both light sources and displays in the visible range through the continuous efforts of researchers, − OLEDs in the DR/NIR region suffer from lower emission efficiencies caused by aggregation-induced quenching, unbalanced charge transport and trapping, and accelerated nonradiative deactivation caused by the energy gap law. − Recently, much progress has been made in developing DR/NIR thermally activated delayed fluorescence (TADF) materials, such as the work of Xu et al demonstrating an external quantum efficiency (EQE) higher than 30% at about 690 nm and very recently Fan et al who developed a multiple subacceptor strategy for constructing NIR-TADF materials and obtained a peak EQE of 21.9% at 712 nm . However, the efficiency roll-off of DR/NIR-OLEDs is still serious at the high-current region. , Although operational stability is one of the key factors in practical application, few reports have given enough attention to the durability of DR/NIR-OLEDs, implying that it is still a great challenge to achieve compatibility of both high performance and excellent operational durability …”