White polymeric light-emitting diode based on a fluorene polymer∕Ir complex blend system

Efficient white-polymeric light-emitting diodes (PLED) were fabricated as a single active layer containing blue-emitting poly(9,9-bis(2-ethylhexyl)fluorene-2,7-diyl) endcapped with bis(4-methylphenyl)phenylamine; (PF2∕6am4), and yellow-orange-emitting iridium [tri-fluorenyl] pyridine complex [$\mathrm{Ir}{\left({\mathrm{Fl}}_3\mathrm{Py}\right)}_3$ ]. The fluorene-like ligands in the blended device prevent phase segregation and also enhance energy transfer from the polymer host to the guest due to efficient overlap of wave function (Dexter process) and host singlet emission and guest absorption bands (Förster process) which reduces the loading level required to produce white emission. The two emitted colors complement each other and doping levels of 2%–3% produce white emission. Above a certain current density, depending on the doping level, the device Commission Internationale de L’Eclairage (CIE) coordinates become bias independent and a stabilized white emission can be obtained. A white-emitting PLED (coordinates 0.348, 0.367) of peak external quantum efficiency of 2.8%, and luminance of $16000\mathrm{cd}∕{\mathrm{m}}^2$ at applied voltage of $5\mathrm{V}$ (i.e., $4.57\mathrm{cd}∕\mathrm{A}$ ) was obtained.