Direct emissive pattern formation in PPV-type polymer with built-in photoresist properties and the application to light emitting devices

The principle of photobleaching in the conjugated polymer material didodecylstilbenevinylene (didodecyl-PSV) was used as a built-in photoresist property to control the extent of the emissive layer in polymer light emitting devices (PLEDs). Illumination of thin films of the conjugated polymer material on optically transparent conducting substrates through a positive mask with short exposure times (20-60 s) using a 150 W Xenon lamp and subsequent application of the and the second electrode enabled the formation of an electroluminescent image of the mask. We demonstrate a direct method where no photoresist, intermediate steps or mechanical manipulation is required to generate a complex emissive pattern employing a homogenous film and homogenous electrodes. The fluorescence of the film showed complex lifetime decays. We found that the lifetime increased with emission wavelength indicating the presence of energetically disordered excitons. The fine structure observed in the solution emission is absent in the film emission. However, after photobleaching the film emission becomes very similar to the solution emission. The appearance of fine structure could indicate that only one state became responsible for the photoluminescence spectrum. Infrared spectroscopy was used to confirm the presence of a degradation route similar to that reported for dialkoxypolyphenylenevinylene materials where the vinylene bonds are react with molecular oxygen and form carboxylic acid groups. Finally the effect of using different electrode metals was established and a comparison made between the photoluminescence and electroluminescence properties. The electroluminescence emission maximum (580 nm) of didodecyl-PSV light emitting devices was found to be redshifted by 20 nm compared to the photoluminescence, exhibited turn-on voltages below 3 V and reached a luminance of 100 cd m−2 at current densities below 10 mA cm−2.