Enhanced light extraction from organic light-emitting devices through non-covalent or covalent polyimide-silica light scattered hybrid films
In this work, two polyimides/silica composites through physical blending (A series) and chemical bonding (B series) were prepared and compared for light extraction from organic light-emitting devices (OLEDs). The physical blending hybrids were prepared from the corresponding poly(amic acid) (PAA) and tetramethyl orthosilicate (TMOS) through thermal imidization and sol-gel process. In contrast, the chemical bonding hybrids series were prepared using 3-aminopropyltriethoxysilane (APTES) as coupling agent followed by sol-gel and thermal imidization process. Their optical, thermal, and morphology properties were investigated. The well-dispersed B series hybrid films showed higher optical transparency and lower haze characteristics than A series. Furthermore, the scattered behavior showed apparently as silica content increasing. They also exhibited high thermal stability with the Td (5 % weight loss temperature) higher than 510 oC. Finally, these hybrid films were applied into OLEDs. The external quantum efficiency (EQE) of all devices applied the hybrid films on the viewer’s side of the substrate as the outcoupling layer are increased as the silica content increasing. For the OLED utilizing A3 (26 wt% of silica content), an increase of light extracting efficiency of 21% was achieved.