Cross-Linkable Polyspirobifluorenes: A Material Class Featuring Good OLED Performance and Low Amplified Spontaneous Emission Thresholds

We report on an in-depth study of cross-linkable polyspirobifluorene (PSF) copolymers for organic lasing applications. We investigate the performance of the materials in organic light-emitting diodes (OLED) and the optically pumped amplified spontaneous emission (ASE) properties of the new PSF-based devices. The influence of chemical composition and cross-linking of the copolymers is investigated. The cross-linkable polymers presented here exhibit low ASE thresholds and simultaneously good OLED efficiencies. This is exceptional. as we demonstrate that usually only one of these properties is optimized in semiconducting polymers. The ASE threshold in the green-emitting materials is as low as 4.4 mu/cm(2) under nanosecond excitation. The chemical cross-linking of the polymers into an insoluble network has little effect on the ASE properties. With the material exhibiting the best figure-of-merit we fabricated a slab-waveguide OLED. This OLED exhibits a low, almost preserved ASE threshold compared to a single layer on glass and concomitantly good luminescence efficiency. Overall, the use of these materials in future organic laser diodes seems promising.