arXiv subjects

Mitchell C. Nelson

Publications and source records attributed to Mitchell C. Nelson.

4 recordsLinked to original sources

arXiv2022

High output efficiency (340 lm/W) in a one wavelength microcavity OLED with emitter layer positioned at an anti-node

An OLED architecture is described in which a thin emitter layer is located at the anti-node of a resonant microcavity. In two realizations, the mode space is constrained by either multi-layer mirrors or by an emitter with transition dipole moments oriented normal to the vertical mode of the device. The multi-layer mirror device achieves 315 lm/W and the oriented emitter device achieves 340 lm/W. Output is observed to be linear in current and efficiency increases with power. This is in agreement with a proposed theoretical model for a microcavity device with emitter located at an anti-node where spontaneous emission is suppressed.

physics.optics↗

arXiv2022

Asymptotic Efficiency in OLEDS

Asymptotic efficiency (high output without droop) was recently reported for OLEDS in which a thin emitter layer is located at the anti-node in a resonant microcavity. Here we extend our theoretical analysis to treat multi-mode devices with isotropic emitter orientation. We recover our efficiency equations for the limiting cases with an isotropic emitter layer located at the anti-node where output is linear in current, and for an isotropic emitter located at the node where output can exhibit second order losses with an overall efficiency coefficient that depends on loss terms in competition with a cavity factor. Additional scenarios are described where output is driven by spontaneous emission, or mixed spontaneous and stimulated emission, with stimulated emission present in a loss mode, potentially resulting in cavity driven droop or output clamping, and where the emitter layer is a host-guest system.

physics.optics↗

arXiv2016

Efficiency and Stimulated Emission in Quarter Wave OLEDS

Quarter-wave OLEDS are microcavity devices that can operate in the low finesse limit and achieve high efficiency (> 300 lm/W) by using interference to reduce the onset current for the transition to stimulated emission. In this work we study the transition to stimulated emission and compare the kinetics and electrical properties of conventional and quarter-wave devices. We show that suppression of spontaneous emission into the vertical mode can result in a sharp transition to stimulated emission at (γ/eV)I ~ N_se/τ_sp where N_se/τ_sp is determined by optical parameters, and we find a previously observed electrical signature for the transition where the excited state population becomes fixed at low current density. We then study the role of loss mechanisms in the quarter-wave configuration and conclude with some requirements for practical device.

physics.optics↗

arXiv2016

Rates and singlet/triplet ratios from TADF transients

Thermally activated delayed fluorescence has been reported in a number of OLED emitter materials engineered to have low singlet-triplet energy gaps. Here we derive closed solutions for steady state and transient behaviors, and apply these results to obtain the singlet and triplet relaxation, forward and reverse crossing rates and the gap energy and reverse crossing prefactor from delayed and prompt relaxation rates measured over a series of temperatures. The primary rates are then used to calculate the fluorescent/phosphorescent ratio and the singlet/triplet population ratio. The method avoids the need for gated yield measurements. Good fits are obtained using previously published data for 4CzIPN and m-MTDATA:t-Bu-PBD and the results appear to be consistent with reported quantities were available, and with reported behaviors of OLEDS that use these materials.

physics.chem-ph↗