AC Field-Induced Polymer Electroluminescence with Single Wall Carbon Nanotubes

Abstract

We developed a high-performance field-induced polymer electroluminescence (FPEL) device consisting of four stacked layers: a top metal electrode/thin solution-processed nanocomposite film of single wall carbon nanotubes (SWNTs) and a fluorescent polymer/insulator/transparent bottom electrode working under an alternating current (AC) electric field. A small amount of SWNTs that were highly dispersed in the fluorescent polymer matrix by a conjugate block copolymer dispersant significantly enhanced EL, and we were able to realize an SWNT-FPEL device with a light emission of approximately 350 cd/m(2) at an applied voltage of ±25 V and an AC frequency of 300 kHz. The brightness of the SWNT-FPEL device is much greater than those of other AC-based organic or even inorganic ELs that generally require at least a few hundred volts. Light is emitted from our SWNT-FPEL device because of the sequential injection of field-induced holes and then electron carriers through ambipolar carbon nanotubes under an AC field, followed by exciton formation in the conjugated organic layer. Field-induced bipolar charge injection provides great material design freedom for our devices; the energy level does not have to be aligned between the electrode and the emission layer, and the balance of the carrier injected and transported can be altered in contrast to that in conventional organic light-emitting diodes, leading to an extremely cost-effective and unified device architecture that is applicable to all red-green-blue fluorescent polymers.

Progress and Prospects in Stretchable Electroluminescent Devices

“…For instance, short carbon nanotube has been demonstrated to increase field strength in the inorganic powder EL devices and reduce operating voltage [48]. Similar performance enhancement was also reported in organic ACEL devices with reduced operating voltage and increased brightness ( 350 cd/m 2 at 25 Vpp) [49]. Other approaches include the use of fluorescent polymer or their hybrids with colloidal quantum dots (QDs) to achieve extremely bright emission at low operating voltage (~500 cd/m 2 at 30 Vpp) [50,51].…”

Increase of electroluminescent intensity in planar light-emitting diode structures based on PFO polymer – ZnO nanoparticles composite films operated by alternating-current voltages

“…AC drive also avoids the charge accumulation in the device due to frequent reversal of the applied bias. Currently the concept of AC-driven organic light-emitting devices drawing much attention because of their unique characteristics such as less dependence on metal electrodes than traditional OLEDs, easy encapsulation and possibility to operate under AC power lines [4][5][6][7][8]. All these features might offer the path towards future highly efficient, flat and flexible light sources.…”

“…The mechanism of charge carrier (electrons and holes) generation in such composites is not known in detail until now. Currently the concept of AC-driven organic light-emitting devices has been applied to OLEDs in traditional sandwich geometry [4][5][6][7][8]. However the effect of application of AC bias to the electrodes of planar light-emitting composite structures is not investigated thoroughly so far.…”

Optimizing the internal electric field distribution of alternating current driven organic light-emitting devices for a reduced operating voltage

“…Several efforts towards AC organic light-emitting devices (AC-OLEDs) have been made in the recent past, and even white-emitting AC-OLEDs have been successfully demonstrated. [4][5][6][7][8] However, the majority of these devices rely on charge injection from one or even both electrodes and show poor performance when operated in a full insulating, capacitively coupled mode, i.e., in a configuration where two insulators prevent charge injection from both electrodes. For this particular configuration, the most promising approach in terms of brightness and efficiency is a p-i-n based architecture in which a single emissive unit is surrounded by doped hole and electron transport layers (HTL/ETL) and by a pair of insulating layers; the whole stack is then sandwiched between two electrodes.…”