J. P. Spindler

Bio: J. P. Spindler is an academic researcher. The author has contributed to research in topics: Phosphorescent organic light-emitting diode & Annihilation. The author has an hindex of 1, co-authored 1 publications receiving 356 citations.

Triplet annihilation exceeding spin statistical limit in highly efficient fluorescent organic light-emitting diodes

Abstract: We have demonstrated that the exemplary red fluorescent organic light-emitting diodes (OLEDs) gain as much as half of their electroluminescence from annihilation of triplet states generated by recombining charge carriers. The magnitude of triplet-triplet annihilation (TTA) contribution in combination with the remarkably high total efficiencies [>11% external quantum efficiency (EQE)] indicates that the absolute amount of electroluminescence attributable to TTA substantially exceeds the limit imposed by spin statistics, which was independently confirmed by studying magnetic field effects on delayed luminescence. We determined the value of 1.3 for the ratio of the rate constants of singlet and triplet channels of annihilation, which is indeed substantially higher than the value of 0.33 expected for a purely statistical annihilation process. It is, however, in an excellent quantitative agreement with the extent of the experimental contribution of delayed luminescence to steady-state electroluminescence. The ...

Efficient blue organic light-emitting diodes employing thermally activated delayed fluorescence

Abstract: Blue organic light-emitting diodes that harness thermally activated delayed fluorescence are realized with an external quantum efficiency of 19.5% and reduced roll-off at high luminance.

Thermally Activated Delayed Fluorescence Materials Towards the Breakthrough of Organoelectronics

Abstract: The design and characterization of thermally activated delayed fluorescence (TADF) materials for optoelectronic applications represents an active area of recent research in organoelectronics. Noble metal-free TADF molecules offer unique optical and electronic properties arising from the efficient transition and interconversion between the lowest singlet (S1) and triplet (T1) excited states. Their ability to harvest triplet excitons for fluorescence through facilitated reverse intersystem crossing (T1→S1) could directly impact their properties and performances, which is attractive for a wide variety of low-cost optoelectronic devices. TADF-based organic light-emitting diodes, oxygen, and temperature sensors show significantly upgraded device performances that are comparable to the ones of traditional rare-metal complexes. Here we present an overview of the quick development in TADF mechanisms, materials, and applications. Fundamental principles on design strategies of TADF materials and the common relationship between the molecular structures and optoelectronic properties for diverse research topics and a survey of recent progress in the development of TADF materials, with a particular emphasis on their different types of metal-organic complexes, D-A molecules, and fullerenes, are highlighted. The success in the breakthrough of the theoretical and technical challenges that arise in developing high-performance TADF materials may pave the way to shape the future of organoelectronics.

Organic light-emitting diodes employing efficient reverse intersystem crossing for triplet-to-singlet state conversion

Abstract: High-efficiency fluorescent organic light-emitting diodes have been realized by employing custom-designed molecules that make it possible to convert non-radiative triplet states into radiative singlet states.

Highly efficient blue electroluminescence based on thermally activated delayed fluorescence.

Abstract: Organic compounds that exhibit highly efficient, stable blue emission are required to realize inexpensive organic light-emitting diodes for future displays and lighting applications. Here, we define the design rules for increasing the electroluminescence efficiency of blue-emitting organic molecules that exhibit thermally activated delayed fluorescence. We show that a large delocalization of the highest occupied molecular orbital and lowest unoccupied molecular orbital in these charge-transfer compounds enhances the rate of radiative decay considerably by inducing a large oscillator strength even when there is a small overlap between the two wavefunctions. A compound based on our design principles exhibited a high rate of fluorescence decay and efficient up-conversion of triplet excitons into singlet excited states, leading to both photoluminescence and internal electroluminescence quantum yields of nearly 100%.

Efficient up-conversion of triplet excitons into a singlet state and its application for organic light emitting diodes

Abstract: A material possessing a very small energy gap between its singlet and triplet excited states, ΔE1−3, which allows efficient up-conversion of triplet excitons into a singlet state and leads to efficient thermally activated delayed fluorescence (TADF), is reported. The compound, 2-biphenyl-4,6-bis(12-phenylindolo[2,3-a] carbazole-11-yl)-1,3,5-triazine, breaks the restriction of a large energy gap, with a ΔE1−3 of just 0.11 eV, while maintaining a high fluorescent radiative decay rate (kr∼107). The intense TADF provides a pathway for highly efficient electroluminescence.