High-efficiency and good color quality white light-emitting devices based on polymer blend

Here we report efficient and color-stable white polymer light-emitting devices (WPLEDs) based on a newly synthesized efficient blue emitting polymer poly[(9,9-bis(4-(2-ethylhexyloxy)phenyl)fluorene)-co-(3,7-dibenziothiene-S,S-dioxide10)] (PPF-3,7SO10) which dually function as host material and blue emitter, with appropriate blending ratio with two typical electroluminescent polymers, green emitting poly[2-(4-(3′,7′-dimethyloctyloxy)-phenyl)-p-phenylenevinylene] (P-PPV) and orange–red emitter poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH–PPV) with appropriate blending ratio. In a single active layer WPLEDs with a blending ratio of 100:0.8:0.5 (B:G:R) by weight, white light emission with CIE coordinate of (0.34, 0.35) was realized. The resulted device shows a high luminous efficiency (LE) of 8.7 cd A−1, which could be further enhanced to 14.0 cd A−1 with incorporation of a thin hole transporting layer poly (vinylcarbazole) (PVK) at the anode side. The obtained luminous efficiency is listed as one of the highest reported value for WPLEDs based on all fluorescent polymer emitters. The devices had appropriate color temperature of 2500–6500 K and high color rendering index (CRI) of 72–79, and are characterized with stable electroluminescent spectra upon change of current density, stress and annealing at high temperature, thus can find application in solid-state lighting.