Regensburg 2002 – wissenschaftliches Programm

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SYOH: Organische Halbleiter

SYOH 5: Organic Light-Emitting Devices

SYOH 5.2: Vortrag

Montag, 11. März 2002, 16:30–16:45, H37

Time gated electroluminescence spectroscopy of polymer light-emitting diodes — •John Lupton and Jens Klein — Max-Planck-Institut fuer Polymerforschung, Ackermannweg 10, D-55128 Mainz

Time gated electroluminescence (EL) spectroscopy is presented as a powerful tool for probing carrier dynamics and trapping in polymer light-emitting diodes (LEDs). The changes in the emission spectrum of single layer polyfluorene diodes containing varying concentrations of a phosphorescent triplet emitter are studied up to 200 us after the driving voltage of the device (typically 5 V) is turned off. By varying the offset of the driving voltage pulse in a range of voltages below the turn-on bias of the device, it is possible to attribute the delayed EL to recombination of comparatively mobile holes with trapped electrons. Two main emission features are observed in the delayed spectra, namely the polymer singlet emission in the blue and a broad defect emission band in the green. The intensity of the green band 20 us after turn-off depends sensitively on the bias offset applied to the voltage pulse, and is found to increase twenty-fold as the bias offset is raised from 0 V to 2.4 V. Upon addition of a phosphorescent host molecule, the delayed recombination kinetics are found to be accelerated and a further narrow emission band is unmasked in the green.