George Pistolis

Incorporating triphenyl sulfonium salts in polyfluorene PLEDs: an all-organic approach to improved charge injection

All-organic sulfonium salts are introduced as a class of ionic compounds that show high compatibility with conjugated polymers and may form blends with attractive luminescent properties leading to significant improvement in single-layer polymer light emitting diodes (PLEDs) performance. We demonstrate that triphenylsulfonium (TPS) triflate:polyfluorene-co-benzothiadiazole (F8BT)-blend based PLEDs show a lower turn-on voltage, an increased luminous efficiency and higher peak luminance values. These results are being rationalized in terms of anionic accumulation and space charge formation at the anode side, which facilitates hole injection, leading to more balanced injection and subsequently to a higher recombination rate. Moreover, we find that the salt anion size plays a critical role in the device operating characteristics. The judicious choice of both the salt and the emitting polymer by considering relative energy level alignment, salt electrochemical stability and acquired thermodynamic stability of blend morphology is important for the achievement of high performance PLEDs without requiring elaborate device architectures.

Effect of triphenylsulfonium triflate addition in wide band-gap polymer light-emitting diodes: improved charge injection, transport and electroplex-induced emission tuning

The presence of mobile anions in the emitting layer of polymer-based OLEDs has been proven to influence substantially the injection characteristics of the diode. In this work we report on the improvement of both injection and transport of charge carriers in blue emitting poly[2-(6-cyano-6-methyl-heptyloxy)-1,4-phenylene] (CN-PPP) based OLEDs upon insertion of the all-organic triphenylsulfonium (TPS) triflate salt in the emitting layer. On one hand, the anion displacement influences the energetics at the polymer/anode interface facilitating hole injection, whereas, on the other hand, the triphenylsulfonium cations act as electron transporting sites. The OLEDs exhibit significantly reduced turn-on voltage to half their initial value and increased luminance at low operating voltage. Moreover, the large energetic mismatch of the polymer and the triphenylsulfonium salt as well as the polarity induced by the ions result in simultaneous dual emission originating from the polymer exciton and from an electroplex, which is proposed to be formed at the triphenylsulfonium salt/polymer interfaces in the bulk. These results show that triphenylsulfonium salts represent an attractive class of materials that can be blended with conjugated polymers and can modify their electrical and/or emissive characteristics.

Third-order nonlinear optical properties of some novel BODIPYs

The nonlinear optical properties of a series of novel boron dipyrromethene derivatives (BODIPY) are investigated by means of the Z-scan technique under 4 ns and 35 ps, visible and infrared laser pulses. All studied BODIPYs were found to exhibit strong saturable absorption and insignificant nonlinear refraction under visible excitation, while no response was observed under infrared laser excitation. The nonlinear optical parameters of the BODIPYs have been determined, revealing large nonlinear absorption coefficient ß values.

Near-IR organic light emitting diodes based on porphyrin compounds

Here we report on organic light-emitting diodes incorporating two porphyrin compounds exhibiting red to near infra-red (IR) emission. Especially, the compound with the long side groups (porphyrin II) has a red-shifted emission (λPLmax = 793 nm) compared to the compound with the single porphyrin ring (porphyrin I, (λPLmax = 723 nm) as a consequence of its extended π-conjugation. We studied the electroluminescence of blends with poly(9-vinyl carbazole) (PVK), achieving high color purity near-infrared electroluminescence.

Polymer photonic technologies for optical communications

The impact of photonics in telecommunications is indisputably massive; however it relies on efficient cost reduction which is in turn only possible if significant cost savings are made at all steps in the development of the photonic device from the material to packaging. The PHOTOPOLIS consortium has identified polymer technology as the ideal solution for producing low-cost devices. The paper aims to discuss the status of polymer photonic components and subsystems able to generate, transmit and manage optical information in a cost effective manner.