Stable white electroluminescence from single fluorene-based copolymers: using fluorenone as the green fluorophore and an iridium complex as the red phosphor on the main chain

Abstract

A series of novel fluorene-based copolymers with fluorenone and an iridium complex on the main chain have been synthesized by Suzuki polycondensation, and characterized by ¹H NMR, ¹³C NMR, and GPC. The TGA results indicate good thermal stability of the copolymers. By incorporating less than 0.15 mol% of both green-emitting fluorenone and red-emitting iridium complex into the copolymers, single copolymers with simultaneous blue-, green- and red-light emission were achieved. Electrochemical study suggests that the fluorenone and iridium complex in the copolymers could function as traps for both electrons and holes. Single-active-layer polymer light emitting devices with the configuration ITO/PEDOT/copolymer/CsF/Al have been fabricated. The device from P3 exhibits a maximum luminance efficiency of 5.50 cd A^–1 with CIE coordinates of (0.32, 0.45) and a maximum luminance of 3361 cd m^–2. The device from P5 shows a maximum luminance efficiency of 3.25 cd A^–1 with color coordinates (0.28, 0.32) and a maximum luminance of 1015 cd m^–2. The white light devices based on P4–P6 exhibit low turn-on voltages around 4.0 V, and their CIE coordinates are insensitive to the applied voltages.