Guillaume Wantz

Temperature-dependent electroluminescence spectra of poly(phenylene-vinylene) derivatives-based polymer light-emitting diodes

This study reports on the temperature dependence of electroluminescence spectra of polymer light-emitting diodes based on poly[2,5-bis(3′,7′-dimethyl-octyloxy)1,4-phenylene-vinylene] and poly[2-methoxy-5(2′-ethyl-hexoxy)1,4-phenylene-vinylene]. Temperatures from 80to350K were investigated. A vibronic structure of electroluminescence spectra has been observed. The electroluminescence spectra were then fitted with multiple Gaussian peaks. A blueshift of the zero-phonon line has been reported with increasing temperature, while the full width at half maximum of electroluminescence peaks increased. We propose a model of thermally activated statistic occupation of excited states to fully describe the experimental data. Finally, these electroluminescence changes with temperature only imply a negligible variation of the emitted color.

White and Saturated Blue Phosphorescent OLED based on the Non-Emissive Homoleptic Complex Ir(ppz)3 as single active material

Abstract The well-known homoleptic iridium (III) complex Ir(ppz)3 which is only emissive in solution at low temperature has been investigated as dopant in a p − i stacked OLED architecture. Interestingly, while using this phosphor as a single emitter, awhite OLED was obtained. Emission colour was determined as being concentration and thickness-dependent.

Bis-Azide Low-Band Gap Cross-Linkable Molecule N3-[CPDT(FBTTh2)2] to Fully Thermally Stabilize Organic Solar Cells Based on P3HT:PC61BM

We synthesized a novel bis-azide low-band gap cross-linkable molecule N3-[CPDT(FBTTh2)2] with wide absorption. This compound is of interest as an additive in polymer/fullerene bulk heterojunction solar cells. In addition to providing efficient thermal stabilization of the morphology, the additive can harvest additional solar light compared with pristine poly(3-hexyl thiophene) to improve the power-conversion efficiency (PCE). The additional donor material was visualized from the appearance of additional external quantum efficiency contributions between 650 and 800 nm. An open-circuit voltage increase of ∼2% compensates the decrease in the short-circuit current of ∼2% to achieve a fully thermally stabilized PCE of 3.5% after 24 h of annealing at 150 °C.

Bulk Electroluminescence from Conjugated Polymer Thin Films via the Formation of Gold Nanoislands

Electroluminescence (EL) from conjugated polymers is commonly realized via polymer light-emitting diodes that are essentially metal/insulator/metal structures. Alternatively, a polymer light-emitting electrochemical cell (LEC) operates by in situ electrochemical doping and the formation of a dynamic p–n junction. An LEC with a stabilized p–n junction is analogous to a conventional inorganic p–n lightemitting diode, where the injection of minority charge carriers results in localized EL in the vicinity of the junction. An LEC consists of a mixture of a semiconducting polymer and a solid-state electrolyte. In the pristine state, free ions are distributed throughout the film and no doping occurs. When a sufficient voltage is applied, the polymer is reduced and oxidized at the cathode and anode, respectively. Mobile ions then rearrange to compensate for the injected charges, electrochemically doping the LEC film starting from the electrodes and progressing toward the center of the device. In most LECs, ion mobility is heavily dependent on temperature, and thus controlling the temperature can control the time to form the p–n junction and turn on the device. The electrochemical doping process responsible for LEC operation makes the device relatively insensitive to electrode materials and highly insensitive to the interelectrode spacing. Fluorescence imaging of extremely large planar LECs enables easy visualization of the dynamic electrochemical-doping and junction-formation processes. Consistent with the electrochemical-junction model described above, the emission zone in a planar LEC is observed to be a single narrow strip only a fraction of the entire interelectrode spacing. Recently, Tracy and Gao demonstrated an innovative and promising LEC device concept by introducing micrometer-