2005
DOI: 10.1063/1.1899751
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Electric field-induced transition from heterojunction to bulk charge recombination in bilayer polymer light-emitting diodes

Abstract: We investigate the photo- and electroluminescence from bilayers of electron- and hole-transporting polyfluorene derivatives at different device temperatures. We show that barrier-free charge capture at the heterojunction is the sole capture mechanism at low driving voltages (below 2.4×105V∕cm2 at room temperature). In this mechanism, which we suggested recently [Morteani et al., Adv. Mater. 15, 1708 (2003)], charge capture produces an interfacial excited state (exciplex) directly and bulk exciton electrolumine… Show more

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Cited by 37 publications
(40 citation statements)
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“…Morteani et al have studied polymer:polymer blends and have shown with temperaturedependent measurements that energy transfer from the CT state dominates below 4V, with an endothermic activation energy of 200 meV ± 50 meV. [51][52][53] Since all of the presented EL spectra have been measured at voltages smaller than 4 V, this would suggest that the principal mechanism is energy transfer from the CT state to a component singlet. The activation energy of 200 meV corresponds to about twice the width of the density of states (DOS) of an organic semiconductor, 54 which may suggest that singlet emission is linked to an overlap of CT state emission and singlet absorption.…”
Section: Discussionmentioning
confidence: 99%
“…Morteani et al have studied polymer:polymer blends and have shown with temperaturedependent measurements that energy transfer from the CT state dominates below 4V, with an endothermic activation energy of 200 meV ± 50 meV. [51][52][53] Since all of the presented EL spectra have been measured at voltages smaller than 4 V, this would suggest that the principal mechanism is energy transfer from the CT state to a component singlet. The activation energy of 200 meV corresponds to about twice the width of the density of states (DOS) of an organic semiconductor, 54 which may suggest that singlet emission is linked to an overlap of CT state emission and singlet absorption.…”
Section: Discussionmentioning
confidence: 99%
“…Polymeric semiconductors are an exciting class of materials that are now finding commercial applications in light-emitting diodes (LEDs) for electroluminescent displays [1][2][3][4] and show promise in other applications such as in photovoltaic diodes (PVDs). [5][6][7][8][9][10] It is now widely accepted that the primary photoexcitations in phenylene-based π-conjugated polymers are singlet excitons, and that these migrate within the bulk polymer phase by incoherent stepwise hops that are mediated by resonance energy transfer (RET).…”
Section: Introductionmentioning
confidence: 99%
“…In some nanocomposites, the existence of new recombination mechanisms is suggested by the generation of new PL emission lines, 35 which may be attributed to the formation of interfacial states termed exciplex. 36 Figure 6 depicts the typical afterglow decay curves of the phosphor samples after the powders were activated using a pulsed xenon lamp. The curves show that the BaAl x O y :Eu 2þ ,Dy 3þ phosphor material emits light far longer than the typical microsecond lifetime of Eu 2þ .…”
Section: X-ray Diffraction (Xrd)mentioning
confidence: 99%