Spectrally-resolved hyperfine interactions between polaron and nuclear spins in organic light emitting diodes: Magneto-EL studies

TL;DR

This study uses spectrally-resolved magneto-electroluminescence to investigate how hyperfine interactions between polarons and nuclear spins vary with energy in organic LEDs, revealing energy-dependent localization effects.

Contribution

It provides the first spectral analysis of hyperfine interactions in organic LEDs, linking energy-dependent EL responses to polaron localization and hyperfine coupling.

Findings

Higher magnetic field effects at blue end of spectrum (~11%) compared to red (~4%)

Magneto-EL curve widths increase from blue to red, indicating stronger hyperfine coupling at lower energies

Energy-dependent spatial extent of polarons inferred from spectral magneto-EL measurements

Abstract

We use spectrally-resolved magneto-electroluminescence (EL) measurements to study the energy dependence of hyperfine interactions between polaron and nuclear spins in organic LEDs. Using layered devices based on Bphen/MTDATA -- a well-known exciplex emitter -- we show that the increase in EL emission intensity $I$ due to small applied magnetic fields of order 100 mT is markedly larger at the high-energy blue end of the EL spectrum (dI/I ~11%) than at the low-energy red end (~4%). Concurrently, the widths of the magneto-EL curves increase monotonically from blue to red, revealing an increasing hyperfine coupling between polarons and nuclei and directly providing insight into the energy-dependent spatial extent and localization of polarons.