Propriedades optoeletrônicas de interfaces híbridas metal/semicondutor orgânico preparadas por deposição assistida por feixe de íons (IBAD) / Optoelectronic properties of interfaces hybrid metal / organic semiconductor prepared by ion beam assisted deposition (IBAD)


IBICT - Instituto Brasileiro de Informação em Ciência e Tecnologia




In this work, optoelectronic properties from organic light emitting devices (OLEDs), based on conjugated polymers with metallic cathode, which were deposited by ion beam assisted deposition technique (IBAD) were studied. The main objective of this work is to produce a hybrid non abrupt metal/polymer interface and to study its effects on electron injection. The use of this technique in organic electronics is incipient, being used in Brazil for the first time. Several exploratory experiments were made, to suit this technology to this new application. The OLEDs devices have a typical vertical-architecture, using Indium Tin Oxide (ITO) covered glass substrate as transparent anode; Poly [ethylene-dioxythiophene]: Poly [styrene sulfonic acid] (PEDOT:PSS) as hole transport layer and polifluorene (PFO) as emitting layer. The cathode layer were deposited over the PFO using IBAD with aluminum and Ar ions, with energies in the range from 0 to 1000 eV. Computer simulations using TRIM code (Transport of Ions in Matter) were done to evaluate the Al penetration into the polymer and the atomic displacement during IBAD process. Fluorescence microscopy, photoluminescence (PL) and Raman spectroscopy were used to study the effects of ions on the polymer layer. The hybrid interface properties were studied with the variation of the active layer thickness and introducing spacing layers of inert polyelectrolyte between the metallic cathode and the PFO. Ions with energy above 400eV decrease polymer electroluminescent properties. Finally, electron injection properties of the cathode were studied using Current Voltage and Electroluminescent measurements. The results show that lower Ar+ ion energies (between 0 and 400 eV) cause a significant shift on the injection voltage. The Current Voltage curves, whose characteristics are modified by IBAD, are described by Fowler Nordheim model. These measurements suggests that Ar+ ion energies between 0 and 80 eV promote the formation of an interface that contains isolated metallic nanoparticles, which may scatter the light. These nanoparticles ease the injection for lower electric fields. The enhancement of the contact between polymer and cathode is observed and is consistent with the reduction of preferred paths during electron injection, which minimizes the problems related to OLEDs efficiency and durability.


contatos elétricos electrical contacts eletrônica orgânica ibad ibad interface metal polímero oled oled organic electronics polymer metal interface

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