A solvent-resistant azide-based hole injection/transporting conjugated polymer for fluorescent and phosphorescent light-emitting diodes

Abstract

Interfacial mixing of polymers is a critical issue when attempting to improve the charge transport and stabilize the operation of solution-processed organic light-emitting diodes (OLEDs). Herein, we describe a simple methodology for overcoming interfacial mixing, based on the use of a photo-crosslinkable hole injection/transporting material (HITM). We synthesized a conjugated polymer, PTCAzide, bearing ready crosslinking ability and investigated its suitability for use as an HITM. Photo-crosslinking of the PTCAzide copolymer gave X-PTCAzide, which exhibited much higher thermal stability (the glass transition temperature increased by 21 K relative to that of PTCAzide), remarkable electrochemical stability, and excellent solvent-resistance, thereby expanding the operation time of corresponding electronic devices. Such a tris(8-hydroxyquinolinato)aluminum-based trilayer device reached a maximum brightness of 52 971 cd m⁻², and the maximum luminance efficiency (LE) and power efficiency (ηE) are both higher than those of the corresponding device based on commercial PEDOT : PSS. In addition, a solution-processed phosphorescent OLED device incorporating X-PTCAzide also exhibited good performance (external quantum efficiency: 7.93%; LE: 29.6 cd A⁻¹; ηE: 14.3 lm W⁻¹; maximum brightness: 34 484 cd m⁻²). The efficient and simple photocrosslinking without adding an initiator could facilitate the fabrication process. Thus, PTCAzide appears to be a promising next-generation HITM for the development of highly efficient and inexpensive OLEDs. Its photo-crosslinkable nature allows improvements in morphological stability and hole injection/transporting ability, leading to more stable devices with better operation, without disrupting molecular packing or charge transport.