Variable‐angle spectroscopic ellipsometry (VASE) has been applied to five polyfluorene gain media. The ellipsometric data have been analyzed using an electronic model based on critical points of zero dimension, i.e., an exciton model. The optical constants of thin‐film samples on spectrosil B substrates have been deduced and are used to characterize the waveguiding conditions in these asymmetric slab structures. The exciton model that we have used leads to a small correlation of the parameters and accurate fits. The good match with normal‐incidence transmission spectrophotometry data and surface profilometry determinations of thickness gives further confidence in the suitability of this model. Based on our measurements, we calculate the cut‐off thicknesses for the fundamental TE‐guided modes in our silica–polymer–air structures to lie within the range of 40 nm to 70 nm (depending on the specific polymer), and demonstrate corresponding confinement factors (Γ) between 37 % and 63 %. The calculated thickness dependence of the cut‐off wavelength agrees well with experimental data for the thickness dependence of the peak amplified spontaneous emission (ASE) wavelength and is, therefore, consistent with previous explanations of the ASE spectral shifts.

We demonstrate that the fast initial decay of a prototypical fluorescent polymer based organic light emitting diode device is related to the contribution that triplet–triplet annihilation makes to the device efficiency. We show that, during typical operating conditions, approximately 20% of the device efficiency originates from the production of singlet excitons by triplet–triplet annihilation. During prolonged device operation, the triplet excitons are quenched much more easily than the emissive singlets; thus, the contribution to the efficiency from triplet–triplet annihilation is lost during the early stages of the device lifetest. The fast initial decay of the device luminance can be removed by incorporating a triplet quenching additive into the active layer to remove any effect of triplet–triplet annihilation; this yields an increase in the device lifetime of greater than 3× and an even more significant improvement in the initial luminance decay.

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A fluorescent blue P-OLED has high densities of triplet excited states within the emissive layer. In this paper we will present an efficiency and degradation analysis of model P-OLED devices and materials, and demonstrate that control of triplet transfer and annihilation processes are of crucial importance in realising the efficiencies and device stabilities required for commercialisation of the technology.

We demonstrate a procedure for fabricating micro-structured organic light-emitting diodes (micro-LEDs) based on so-called breath figure (BF) pattern formation. In the latter process water vapour is condensed on the surface of a spread polymer solution to form droplets that close pack into ordered arrays and that transfer the BF pattern into the resulting solid thin polymer film. Here, we generate a silicone elastomer negative replica of the BF pattern and use it as a master for solvent-assisted micro-moulding of an insulating polymer layer deposited on top of a PEDOT:PSS covered indium tin oxide (ITO)-coated glass substrate. By spin coating a light-emitting polymer blend film on top of the micro-structured insulator, we obtain micro-structured polymer LEDs with dimensions defined by the BF pattern.