Studies on the long-term degradation of organic light-emitting devices (OLEDs) based on tris(8-hydroxyquinoline) aluminum (AlQ3), the most widely used electroluminescent molecule, reveal that injection of holes in AlQ3 is the main cause of device degradation. The transport of holes into AlQ3 caused a decrease in its fluorescence quantum efficiency, thus showing that cationic AlQ3 species are unstable and that their degradation products are fluorescence quenchers. These findings explain the success of different approaches to stabilizing OLEDs, such as doping of the hole transport layer, introducing a buffer layer at the hole-injecting contact, and using mixed emitting layers of hole and electron transporting molecules.

Poly(4,8-dialkyl-2,6-bis(3-alkylthiophen-2-yl)benzo[1,2-b:4,5-b‘]dithiophene) 1 represents a new class of polymer semiconductors which self-assemble into higher structural orders without thermal annealing and provide excellent field-effect transistor performance with mobility up to 0.25 cm2 V-1 s-1 when used as a solution-processed thin-film semiconductor in thin-film transistors.

The intrinsic degradation of tris(8-hydroxyquinoline) aluminum (AlQ3)-based organic light emitting devices, that leads to the long-term decrease in the electroluminescence efficiency of the devices operated under constant current conditions, is studied. The injection of holes in A1Q3 is found to be the main factor responsible for device degradation. OLEDs with dual HTLs in different arrangements are also presented to demonstrate the proposed degradation mechanism. The role of various approaches to increase OLED lifetime, such as, doping the hole transport layer, introducing a buffer layer at the hole-injecting contact, or using a mixed emitting layer of hole and electron transporting molecules, is explained.

We report electroluminescence degradation studies of tris (8-hydroxyquinoline) aluminum (Alq3) organic light-emitting devices (OLEDs) under ambient conditions. Alq3 films and organic bilayer anode/naphthyl-substituted benzidine derivative/Alq3/cathode devices are studied via electroluminescence, photoluminescence, polarization microscopy and atomic force microscopy, and via microscopic infrared spectroscopy. Results reveal that humidity induces the formation of crystalline Alq3 structures in originally amorphous films. The same phenomenon is found to occur in OLEDs and causes cathode delamination at the Alq3/cathode interface that results in the formation of black (nonemissive) spots in the devices.

We report electroluminescence degradation studies on tris(8-hydroxyquinoline) aluminum (Alq3)-based organic light emitting devices (OLEDs) with Mg:Ag cathodes in ambient conditions. The nonemissive spots in the OLEDs are studied via optical and fluorescence microscopy and via microscopic infrared spectroscopy. Studies reveal that a majority of the nonemissive spots are caused by the growth of Mg(OH)2 sites at the Alq3/Mg:Ag interface, associated with local degradation of the Alq3 layer. In addition, the growth of elevated cathode bubbles, which also lead to nonemissive spots, is found to be caused by gas evolution from the galvanic corrosion of the Mg/Ag couple as well as from the electrolysis of absorbed moisture.

Quadrupole echo deuterium NMR has been used to probe the dynamics of poly(vinyl acetate-d3) in bulk and at saturation coverage (from toluene) on silica at the solid-air interface. In bulk and at lower temperatures, the deuterium powder pattern of the labeled methyl group was found to be consistent with fast threefold jumps with a small asymmetry due to the interaction of the methyl deuteron with the carbonyl oxygen. This apparent asymmetry was a result either of a distortion in the C-C-D bond angle or a reduction of the axial symmetry of the electric field gradient along the C-D bond vector. At higher temperatures, the onset of backbone motion of the polymer caused the collapse of the powder pattern to a single broad resonance over a fairly small temperature range between 65 and 73 °C. The collapse was well above the glass transition temperature as measured by differential scanning calorimetry, Tg(DSC)) 32 °C, and can be considered the Tg(NMR). The differences in temperatures for these two experiments are due to their different time scales. For the PVAc-d3 adsorbed at monolayer coverage on a silica surface, a small fraction was found to result in a collapsed powder pattern below the Tg(NMR). This fraction with enhanced mobility was believed to be located near the air-polymer interface. The powder pattern for the majority of the surface-bound polymer was found to collapse gradually with temperature, with a rigid component observable well above the temperature where the splittings for all of the bulk material had collapsed. Thus, from the deuterium NMR spectra, it is possible to deduce that on a surface, different segments from a single molecule exhibit a range of mobilities.

The synthesis of novel regioregular poly (4,8-didodecylbenzo[1,2-b:4,5-b′]dithiophene) and its use as a semiconductor in organic thin-film transistors (OTFTs) are described. The polymer was prepared from 2,6-dibromo-4,8-didodecylbenzo[1,2-b:4,5-b′]dithiophene by a dehalogenative coupling polymerization. A field-effect mobility of ∼0.012 cm 2 V -1 s -1 and a current on/off ratio of ∼2.5 × 10 5 have been obtained with OTFTs using this polymer semiconductor.

Poly(4,8‐didodecyl‐2,6‐bis‐(3‐methylthiophen‐2‐yl)‐benzo[1,2‐b:4,5‐b′]dithiophene) self‐assembled on appropriate substrates from solution and formed highly structured thin films at low temperatures. As an as‐prepared thin‐film semiconductor without thermal annealing, it exhibited excellent field‐effect transistor properties with mobility of ∼ 0.15 cm2 V–1 s–1 in thin‐film transistors.