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Organic Light-Emitting Transistors with Simultaneous Enhancement of Optical Power and External Quantum Efficiency via Conjugated Polar Polymer Interlayers
journal contribution
posted on 2018-07-09, 00:00 authored by Mario Prosa, Emilia Benvenuti, Mariacecilia Pasini, Umberto Giovanella, Margherita Bolognesi, Lorenzo Meazza, Francesco Galeotti, Michele Muccini, Stefano ToffaninOrganic
light-emitting transistors (OLETs) show the fascinating
combination of electrical switching characteristics and light generation
capability. However, to ensure an effective device operation, an efficient
injection of charges into the emissive layer is required. The introduction
of solution-processed conjugated polyelectrolyte (CPE) films at the
emissive layer/electrode interface represents a promising strategy
to improve the electron injection process by dipole formation. However,
their use in optoelectronic devices also involves some limitations
because of the ionic nature of CPEs. In this context, neutral conjugated
polar polymers (CPPs) represent a valid alternative to CPEs because
the conjugated backbones of CPPs are functionalized with polar nonionic
side groups, thus avoiding ion-dependent drawbacks. By introducing
a layer of polyfluorene-containing phosphonate groups underneath the
metal electrodes, we here demonstrate a substantial improvement of
the electron injection properties into the OLET-emissive layer and,
accordingly, a more than 2-fold increased light power and a 5 times
higher external quantum efficiency of p-type OLETs in comparison with
reference devices without any interlayer. The great benefit of using
a transparent glass substrate allowed to selectively investigate the
morphological and photoluminescent characteristics of both CPE- and
CPP-buried interlayers within complete OLETs by means of an optical
scanning probe technique. This, together with a thorough optoelectronic
characterization of the figures of merit of working light-emitting
devices, allowed to disclose the origin of the improved optical performance
of CPP-based devices as well as the operation mechanisms of the investigated
interlayer in the corresponding OLETs.
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Keywords
polyfluorene-containing phosphonate groupsCPEside groupsion-dependent drawbacksCPP-buried interlayersp-type OLETsscanning probe techniqueoptoelectronic characterizationdevice operationreference devicesOptical PowerExternal Quantum EfficiencyOrganic Light-Emitting Transistorselectron injection propertiesglass substratequantum efficiencyelectron injection processConjugated Polar Polymer Interlayers Organic light-emitting transistorsemissive layeroperation mechanismsOLET-emissive layerSimultaneous Enhancementlight generation capabilityCPP-based deviceslight powermetal electrodes5 timeslight-emitting devicesoptoelectronic devicesphotoluminescent characteristics
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