Design of efficient molecular organic light-emitting diodes by a high-throughput virtual screening and experimental approach.

Virtual screening is becoming a ground-breaking tool for molecular discovery due to the exponential growth of available computer time and constant improvement of simulation and machine learning techniques. We report an integrated organic functional material design process that incorporates theoretical insight, quantum chemistry, cheminformatics, machine learning, industrial expertise, organic synthesis, molecular characterization, device fabrication and optoelectronic testing. After exploring a search space of 1.6 million molecules and screening over 400,000 of them using time-dependent density functional theory, we identified thousands of promising novel organic light-emitting diode molecules across the visible spectrum. Our team collaboratively selected the best candidates from this set. The experimentally determined external quantum efficiencies for these synthesized candidates were as large as 22%.

A Novel Design Strategy for Suppressing Efficiency Roll-Off of Blue Thermally Activated Delayed Fluorescence Molecules through Donor-Acceptor Interlocking by C-C Bonds.

The short material lifetime of thermally activated delayed fluorescence (TADF) technology is a major obstacle to the development of economically feasible, highly efficient, and durable devices for commercial applications. TADF devices are also hampered by insufficient operational stability. In this paper, we report the design, synthesis, and evaluation of new TADF molecules possessing a sterically twisted skeleton by interlocking donor and acceptor moieties through a C-C bond. Compared to C-N-bond TADF molecules, such as CPT2, the C-C-bond TADF molecules showed a large dihedral angle increase by more than 30 times and a singlet-triplet energy-gap decrease to less than 0.22 eV because of the steric hindrance caused by the direct C-C bond connection. With the introduction of a dibenzofuran core structure, devices comprising BMK-T317 and BMK-T318 exhibited a magnificent display performance, especially their external quantum efficiencies, which were as high as 19.9% and 18.8%, respectively. Moreover, the efficiency roll-off of BMK-T318 improved significantly (26.7%). These results indicate that stability of the material can be expected through the reduction of their singlet-triplet splitting and the precise adjustment of dihedral angles between the donor-acceptor skeletons.

Versatile Molecular Functionalization for Inhibiting Concentration Quenching of Thermally Activated Delayed Fluorescence.

Concentration quenching of thermally activated delayed fluorescence is found to be dominated by electron-exchange interactions, as described by the Dexter energy-transfer model. Owing to the short-range nature of the electron-exchange interactions, even a small modulation in the molecular geometric structure drastically affects the concentration-quenching, leading to enhanced solid-state photoluminescence and electroluminescence quantum efficiencies.

An Alternative Host Material for Long-Lifespan Blue Organic Light-Emitting Diodes Using Thermally Activated Delayed Fluorescence.

It has been challenging to find stable blue organic light emitting diodes (OLEDs) that rely on thermally activated delayed fluorescence (TADF). Lack of stable host materials well-fitted to the TADF emitters is one of the critical reasons. The most popular host for blue TADF, bis[2-(diphenylphosphino)phenyl] ether oxide (DPEPO), leads to unrealistically high maximum external quantum efficiency. DPEPO is however an unstable material and has a poor charge transporting ability, which in turn induces an intrinsic short OLED operating lifespan. Here, an alternative host material is introduced which educes the potential efficiency and device lifespan of given TADF emitters with the appropriateness of replacing the most popular host material, DPEPO, in developing blue TADF emitters. It simultaneously provides much longer device lifespan and higher external quantum efficiency at a practical brightness due to its high material stability and electron-transport-type character well-fitted for hole-transport-type TADF emitters.

High efficiency pure blue thermally activated delayed fluorescence molecules having 10H-phenoxaborin and acridan units.

Highly efficient blue thermally activated delayed fluorescence molecules having 10H-phenoxaborin and acridan units were reported. Pure blue emission peaking at around 450 nm with a high external electroluminescence quantum efficiency of around 20% was demonstrated.

High-efficiency organic light-emitting diodes with fluorescent emitters.

Fluorescence-based organic light-emitting diodes have continued to attract interest because of their long operational lifetimes, high colour purity of electroluminescence and potential to be manufactured at low cost in next-generation full-colour display and lighting applications. In fluorescent molecules, however, the exciton production efficiency is limited to 25% due to the deactivation of triplet excitons. Here we report fluorescence-based organic light-emitting diodes that realize external quantum efficiencies as high as 13.4-18% for blue, green, yellow and red emission, indicating that the exciton production efficiency reached nearly 100%. The high performance is enabled by utilization of thermally activated delayed fluorescence molecules as assistant dopants that permit efficient transfer of all electrically generated singlet and triplet excitons from the assistant dopants to the fluorescent emitters. Organic light-emitting diodes employing this exciton harvesting process provide freedom for the selection of emitters from a wide variety of conventional fluorescent molecules.