Realization of highly efficient white polymer light-emitting devices via interfacial energy transfer from poly(N-vinylcarbazole)

We report highly efficient white polymer light-emitting devices (WPLEDs) using a newly synthesized, deep-blue emitting fluorene-co-dibenzothiophene-S,S-dioxide copolymer as host, doped with two narrow-bandgap iridium complexes. Despite the low-lying triplet energy levels of the host, phosphorescent quenching by the polyfluorene copolymer host was significantly suppressed with poly(N-vinylcarbazole) (PVK) as hole-injecting, anode buffer layer. The energy transfer process had been studied via transient photoluminescence spectra and confirmed that PVK layer is responsible for the efficient electrophosphorescence in the devices. As a result of balanced red-green-blue (RGB) emission from the host and the triplet emitters, white emission with Commission Internationale de L'Eclairage (CIE) coordinates of (0.278, 0.312) was achieved, with a peak luminous efficiency of 15.1 cd A^-1 and a color rendering index (CRI) of 79-86.