Melt-processing of highly crystalline organic semiconducting layers for organic optoelectronics

摘要

Organic semiconductors have been intensively investigated and used in a variety of organicoptoelectronic devices such as organic light-emitting diodes (OLEDs), organic lasers, organic solar cellsand organic field-effect transistors. A number of different techniques including vacuum vapor depositionand spin-coating have been used to deposit them into thin films. Here, we report on an improvedsolvent-free and vacuum-free melt-processing method to prepare organic semiconducting films with largecrystal size.For this purpose, we used a solution-processable oligo(p-phenylene vinylene) derivativesubstituted at both extremities with pyrene moieties. Compared to previous protocols already reported inthe literature, our work provides evidence that an accurate control of the temperature during therecrystallization of this material from the melt allows the formation of large single crystal monodomains inthe films. As a consequence of the presence of these large-size crystalline monodomains, themelt-processed organic films exhibit in transistor configuration higher charge carrier mobilities than inspin-coated polycrystalline thin films. We then investigated the photophysical and amplified spontaneousemission properties of the spin-coated and melt-processed thin films. The photoluminescence quantumyield was found to increase with the extent of crystallinity of the organic layer, due to a reduction of thenumber of grain boundaries. In addition, amplified spontaneous emission could be observed only in themelt-processed film. Overall, this work shows a simple and versatile melt-processing method to fabricateorganic layers with large crystal size, suitable for the realization of organic electronic and light-emittingdevices.