Solution Processed WPLEDs with Good Color Stability and High Color Rendering Index via a Phosphor-Sensitized System

Abstract

We present efficient, solution processed white polymer light emitting diodes (WPLEDs) with good color stability and high color rendering index (CRI) via a phosphor-sensitized system using blue phosphorescent dye Bis[2-(4,6-difluorophenyl)pyridinato-C2,N](picolinato)iridium(III) (FIrpic) as emitter and sensitizer, and the fluorescent dye Rubrene and 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) as yellow and orange/red emitter respectively. Two different fluorophores, Rubrene and DCJTB, were chosen due to their different emission zone and different charge trapping ability. WPLEDs, in which FIrpic with Rubrene or DCJTB is doped at different feed ratios into poly (N-vinylcarbazole) (PVK) host, were fabricated and the effect of their concentration on the current density v/s voltage (J−V) characteristics and the electroluminescence (EL) spectra were studied. WPLEDs made with FIrpic:Rubrene (10:1) and FIrpic:DCJTB (80:1) were found to give CIE coordinates of (0.30, 0.42) and (0.34, 0.40) with CRI value of 58 and 76 at luminous efficiencies of 4.91 cd A−1 and 2.79 cd A−1 respectively. Finally, FIrpic, Rubrene and DCJTB were doped into PVK to get high quality white light and CIE coordinates of (0.41, 0.43) with a CRI value of 78 at luminous efficiency of 4.73 cd A−1 was achieved for FIrpic:Rubrene:DCJTB feed ratio of (100:8:1).