Extending Anisotropy Dynamics of Light‐Emitting Dipoles as Necessary Condition Toward Developing Highly‐Efficient OLEDs

Abstract

Designing in‐plane‐oriented light‐emitting dipoles is known as a critical method to develop high‐efficiency organic light‐emitting diodes (OLEDs) by enhancing light extraction. However, in‐plane‐oriented light‐emitting dipoles must demonstrate sufficient polarization memory extended into light emission lifetime window, generating extended anisotropy dynamics shown as the necessary condition to increase light extraction toward developing high‐efficiency OLEDs. This paper reports experimental studies on anisotropy dynamics of light‐emitting dipoles in both time and energy domains by using time‐resolved and steady‐state photoluminescence anisotropy measurements based on the in‐plane oriented exciplex‐heterostructured [BCzPh:CN‐T2T] host dispersed with phosphorescent molecules. It is found that, when host–guest Coulomb scattering is suppressed by parallel placing of the in‐plane‐configured phosphorescent Ir(ppy)2(acac) molecules into the in‐plane‐oriented exciplex‐heterostructured [BCzPh:CN‐T2T] host, the anisotropy dynamics of light‐emitting dipoles can be extended into microseconds time window comparable with its phosphorescence lifetime, satisfying the necessary condition in time domain to increase light out‐coupling efficiency toward developing high external quantum efficiencies (EQEs) in Ir(ppy)2(acac):exciplex system. More importantly, by suppressing host–guest Coulomb scattering, the high‐energy transition dipoles can still maintain extended anisotropy dynamics in the energy domain in Ir(ppy)2(acac):exciplex system while hot electrons are relaxing toward lowest unoccupied molecular orbital (LUMO). Consequently, the extended anisotropy dynamics of light‐emitting dipoles demonstrate a high EQE of 34.01% in the Ir(ppy)2(acac):exciplex OLED.

Developing efficient small molecule-based organic photo-couplers by optimizing the cathode interfacial layer in the photodetector

“…45–47 Recently, Wang et al reported the anisotropic dynamics of iridium complexes (Ir(ppy) 3 and Ir(ppy) 2 acac) with different structural symmetries in the BCzPh:CN-T2T exciplex co-host, demonstrating that the low Coulomb scattering effect in the structure of BCzPh:CN-T2T:Ir(ppy) 2 acac maintains strong anisotropic dynamics and high-energy transition dipoles. 48 In a previous study, PO-01 was also promoted as an emitter with a high photoluminescence quantum yield achieving 88%. 49 Based on those reports, the blend structure of BCzPh:CN-T2T:PO-01 is proposed in this study following the hypothesis that iridium complex PO-01 has a similar molecular structure and energy transfer mechanism with Ir(ppy) 2 acac.…”

Transparent organic upconversion devices displaying high-resolution, single-pixel, low-power infrared images perceived by human vision

“…The strong correlation between the infrared intensity and the upconversion luminance substantiated the strategy of using BCzPh:CN-T2T cohost phosphorescence light–emissive system ( 8 ). The bipolar exciplex blend generating spin-orbital coupling for intermolecular charge transfer could harness the nonradiative triplet excitons and facilitate the energy transfer toward the phosphorescent emitter ( 39 ). It was advised that the subgap turn-on voltage (2.0 V at 0.1 cd m −2 ), which is lower than the bandgap energy of the emitter [2.37 eV of Ir(ppy) 2 (acac) in our case] could be assigned to the photovoltaic effect of the CGL ( 40 ).…”

Enhancing Tandem Organic Light-Emitting Diode Performance with Multiple Electroluminescent Units

“…80%), which improves the external outcoupling efficiency of the device and suppresses Coulomb scattering during the energy transfer process from the exciplex co-host, realizing excellent EL efficiency. 49 The D and A molecules are usually selected as the carrier transport layer adjacent to the exciplex co-host EML, which could eliminate the carrier barrier at the HTL/EML and EML/ETL interfaces, thereby lowering the operating voltages. In addition, since the D and A molecules (i.e., BCzPh and CN-T2T) could be, respectively, used for the HTL and ETL, their sufficient carrier mobility could also enhance the current density of the EML.…”

“…Ir­(ppy) 2 acac in this EML configuration has a high horizontal dipole ratio (ca. 80%), which improves the external outcoupling efficiency of the device and suppresses Coulomb scattering during the energy transfer process from the exciplex co-host, realizing excellent EL efficiency . The D and A molecules are usually selected as the carrier transport layer adjacent to the exciplex co-host EML, which could eliminate the carrier barrier at the HTL/EML and EML/ETL interfaces, thereby lowering the operating voltages.…”

“…In addition, the absence of the emission originated from BCzPh or CN-T2T, indicating that the exciplex host could offer effective exothermic energy transfer from the host to the emitter and avoid exciton migration to the adjunct layers. 49 The EL spectral profiles of devices T2, T3, and T3D are different from those of conventional device S because of the optical path difference caused by the complex architecture of the tandem devices and the accompanying microcavities. It is worth noting that the spectral profile of device T3D was nearly identical to that of device S, illustrating the utility of the TiO 2 NPs-based diffuser for eliminating microcavity effects.…”