Hajime Nakanotani

Organic light-emitting diodes (OLEDs) are attractive for next-generation displays and lighting applications because of their potential for high electroluminescence (EL) efficiency, flexibility and low-cost manufacture. Although phosphorescent emitters containing rare metals such as iridium or platinum produce devices with high EL efficiency, these metals are expensive and their blue emission remains unreliable for practical applications. Recently, a new route to high EL efficiency using material

Reverse intersystem crossing (RISC) from the triplet to singlet excited state is an attractive route to harvesting electrically generated triplet excitons as light, leading to highly efficient organic light-emitting diodes (OLEDs). An ideal electroluminescence efficiency of 100% can be achieved using RISC, but device lifetime and suppression of efficiency roll-off still need further improvement. We establish molecular design rules to enhance not only the RISC rate constant but also operational s

Organic light-emitting diodes (OLEDs) are attractive for next-generation displays and lighting applications because of their potential for high electroluminescence (EL) efficiency, flexibility and low-cost manufacture. Although phosphorescent emitters containing rare metals such as iridium or platinum produce devices with high EL efficiency, these metals are expensive and their blue emission remains unreliable for practical applications. Recently, a new route to high EL efficiency using material

Harvesting excited spin-triplet states as light is essential to realize highly efficient electroluminescence (EL) in organic light-emitting devices. In recent years, thermally activated delayed fluorescence (TADF) has attracted much attention as a novel electronic transition process, since it enables harvesting electrically generated triplet energy as EL without the utilization of rare metals such as iridium and platinum. When the energy gap between the excited spin-triplet and spin-singlet stat

Exciplex system exhibiting thermally activated delayed fluorescence (TADF) holds a considerable potential to improve organic light-emitting diode (OLED) performances. However, the operational lifetime of current exciplex-based devices, unfortunately, falls far behind the requirement for commercialization. Herein, rationally choosing a TADF-type electron acceptor molecule is reported as a new strategy to enhance OLEDs' operating lifetime. A comprehensive study of the exciplex system containing 9,

Understanding exciton behavior in organic semiconductor molecules is crucial for the development of organic semiconductor-based excitonic devices such as organic light-emitting diodes and organic solar cells, and the tightly bound electron-hole pair forming an exciton is normally assumed to be localized on an organic semiconducting molecule. We report the observation of long-range coupling of electron-hole pairs in spatially separated electron-donating and electron-accepting molecules across a 1

Abstract By doping 2,7‐bis[4‐( N ‐carbazole)phenylvinyl]‐9,9′‐spirobifluorene (spiro‐SBCz) into a wide energy gap 4,4′‐bis(9‐carbazole)‐2,2′‐biphenyl (CBP) host, we demonstrate an extremely low ASE threshold of E th = (0.11 ± 0.05) μJ cm –2 (220 W cm –2 ) which is the lowest ASE threshold ever reported. In addition, we confirmed that the spiro‐SBCz thin film functions as an active light emitting layer in organic light‐emitting diode (OLED) and a field‐effect transistor (FET). In particular, we s

Harvesting of both triplets and singlets yields electroluminescence quantum efficiencies of nearly 100% in organic light-emitting diodes (OLEDs), but the production efficiency of excitons that can undergo radiative decay is theoretically limited to 100% of the electron-hole pairs. Here, breaking of this limit by exploiting singlet fission in an OLED is reported. Based on the dependence of electroluminescence intensity on an applied magnetic field, it is confirmed that triplets produced by single

To reduce the threshold current density and move closer toward the realization of future current‐injection organic semiconductor lasers, the harvesting of triplet excitons is anticipated because 75% excitons are directly formed as triplet excited states under electrical excitation according to spin statics. However, the observation of light amplification in pure phosphorescent or thermally activated delayed fluorescence (TADF) materials has nor yet been reported even under optical excitation. He

Three thermally activated delayed fluorescence (TADF) molecules, namely PQ1, PQ2, and PQ3, are composed of electron-accepting (A) tetrabenzo[a,c]phenazine (TBPZ) and electron-donating (D) phenoxazine (PXZ) units are designed and characterized. The combined effects of planar acceptor manipulation and high steric hindrance between D and A units endow high molecular rigidity that suppresses nonradiative decay of the excitons with improved photoluminescence quantum yields (PLQYs). Particularly, the

We observed a significant decrease in electroluminescence (EL) in the high-current-density region (J>1A∕cm2) in organic light-emitting diodes (OLEDs). The decreased external quantum efficiency (ηext) in an OLED with a cathode diameter of d=50μm was in excellent agreement with the singlet–singlet annihilation (SSA) model. In contrast, the decreased ηext in an OLED with a cathode diameter of d=1000μm coincided well with the singlet-heat annihilation (SHA) model. These results suggest that l

Single crystal organic field-effect transistors (FETs) based on highly luminescent oligo(p-phenylenevinylene) (OPV) derivatives are fabricated. Although OPV single crystal FETs show both p- and n- type FET operation, we found that an increase in the conjugation length of the OPV derivatives from three phenylene rings (P3V2) to four phenylene rings (P4V3) results in an improvement in the electron mobility by an order of magnitude, while retaining the high hole mobility. This molecular design, usi

Abstract The effect of dye‐doping in ambipolar light‐emitting organic field‐effect transistors (LE‐OFETs) is investigated from the standpoint of the carrier mobilities and the electroluminescence (EL) characteristics under ambipolar operation. Dye‐doping of organic crystals permits not only tuning of the emission color but also significantly increases the efficiency of ambipolar LE‐OFETs. A rather high external EL quantum efficiency (∼0.64%) of one order of magnitude higher than that of a pure p