Abstract:

The development of white organic light-emitting devices(WOLEDs) generated lots of interests in this area, as these devices can be employed not only as illumination light source but also as backlight source candidate for next generation flat-panel displays. To achieve white emission from OLEDs, an additive mixture of three primary colors. i.e., red, green, and blue(RGB) or a complementary color modification is indispensable. Comparing to the undoped device, the performances of doped red OLEDs and blue OLEDs were enhanced. Thereafter doping highly fluorescent dyes in emission layer became an important approach to realize WOLEDs with excellent performance. WOLEDs based on an ultrathin layer of yellow fluorescent dye 5,6,11,12-tetraphenylnaphthacene(Rubrene) were investigated. By changing the thickness of ultrathin dye layer fabricated by thermal vacuum deposition and analyzing electroluminescent(EL) spectra of devices, concentration effect of dye on the performance of the devices was analyzed. The results showed that the balanced intensity of yellow and blue light for white light emission was obtained in the device when the thickness of fluorescent dye Rubrene was 0.3 nm. The blue light emitted from fluorescent material N,N′-bis-(1-naphthyl)-N,N′-biphe-nyl-1,1′-biphenyl-4,4′-diamine(NPB) and the yellow light was from fluorescent Rubrene dye. A maximum luminance of 3700 cd/m2 was obtained. The Commissions International L′Eclairage(CIE) coordinates located at(0.32, 0.33), which is almost consistent with the optimum white CIE of (0.333, 0.333). The high performance of WOLED was ascribed to direct carrier trapping(DCT) effect of Rubrene and efficient energy transfer from NPB to Rubrene.

Key words: Organic light-emitting devices(OLEDs); White light; Ultrathin layer; Fluorescent dye; Rubrene