Solution processed single-emission layer white polymer light-emitting diodes with high color quality and high performance from a poly(N-vinyl)carbazole host

Abstract

Low cost and high performance white polymer light-emitting diodes (PLEDs) are very important as solid-state lighting sources. In this research three commercially available phosphors were carefully chosen, bis[2-(4,6-difluorophenyl)pyridinato-N,C²](picolinate)iridium(III) (FIrpic), bis[2-(2-pyridinyl-N)phenyl-C](2,4-pentanedionato-O²,O⁴)iridium(III) [Ir(ppy)₂(acac)], and bis(2-phenyl-benzothiazole-C²,N)(acetylacetonate)iridium(III) [Ir(bt)₂(acac)], plus a home-made red phosphor of tris[1-(2,6-dimethylphenoxy)-4-(4-chlorophenyl)phthalazine]iridium(III) [Ir(MPCPPZ)₃], and their photophysical and morphological properties were systematically studied as well as their applications in single-emission layer white PLEDs comprising poly(N-vinylcarbazole) as host. Additionally, the electrochemical properties and energy level alignment, possible energy transfer process, and thin-film morphology were also addressed. The binary blue/orange complementary white PLEDs exhibit stable electroluminescence spectra, wide spectrum-covering region range from 380–780 nm, and high color rendering index (CRI) over 70 with Commission Internationale de l'Eclairage coordinates x,y (CIE_x,y) of (0.388, 0.440), correlated color temperature (CCT) of around 4400, plus high efficiency of 25.5 cd A⁻¹. The optimized red–green–blue white PLEDs showed a satisfactory CRI of around 82.4, maximum current efficiency of 20.0 cd A⁻¹ and external quantum efficiency (EQE) of 10.8%, corresponding to a CCT of 3700–2800, which is a warm-white hue. At last, stable and high color quality, red–green–orange–blue four component white PLEDs, with a CRI of over 82, a high efficiency of 24.0 cd A⁻¹, EQE of 11.5%, and high brightness of 43 569.9 cd m⁻² have been obtained.