High-color-rendering-index white polymer light-emitting electrochemical cells based on ionic host-guest systems: Utilization of blend films of blue-fluorescent cationic polyfluorenes and red-phosphorescent cationic iridium complexes

The authors present high-color-rendering-index (CRI) white polymer light-emitting electrochemical cells (PLECs) based on ionic host-guest systems. PLECs were fabricated with blend films composed of a blue fluorescent cationic pi-conjugated polymer, poly(9,9-bis[60-(N, N, N,-trimethylammonium) hexyl] fluorineco- alt-1,4-phenylene) bromide (PFN+Br-), used as a host, and a red phosphorescent cationic iridium complex, [ Ir(ppy)(2)(biq)](+)(PF6)(-) (where (ppy)(-) = 2-phenylpyridinate and biq = 2,2'-biquinoline), used as a guest. By optimizing the composition of PFN+Br- and [Ir(ppy)(2)(biq)](+)(PF6)(-) in the active layers, white light emission with Commission Internationale de l'Eclairage (CIE) coordinates of (x = 0.28, y = 0.31) and a very high CRI of 95.8 was achieved through mixing of blue and red light at an applied voltage of 4.0 V. The white light emissions were obtained at a low [Ir(ppy)(2)(biq)](+)(PF6)(-) concentration (PFN+Br- :[Ir(ppy)(2)(biq)](+)(PF6)(-) = 1: 0.01 (mass ratio)), showing that [Ir(ppy)(2)(biq)](+)(PF6)(-) acts as a suitable energy acceptor. The emission mechanism of the ionic host-guest PLECs can be explained by Forster resonance energy transfer (FRET) and Dexter energy transfer (DET) from the excited PFN+Br- to [Ir(ppy)(2)(biq)](+)(PF6)(-). Utilization of ionic host-guest PLECs is a very promising method for realizing white light-emitting devices with very high CRI. (C) 2017 Elsevier B.V. All rights reserved.