A bright, transparent, blue organic light emitting device

Abstract

Organic light emitting devices (OLEDs) which emit in the red, green and blue spectral regions are well-known. A unique property of vacuum-deposited OLEDs is that the luminescence band is red shifted from the absorption band by as much as 0.5 eV, potentially making OLEDs highly transparent throughout the visible spectrum. Such transparency offers the potential for realizing a full-color display in which the red (R), green (G), and blue (B) emission layers are placed in a vertically stacked geometry to provide minimum R-G-B pixel size and maximum fill factor. Other obvious applications for transparent OLEDs (TOLEDs) include helmet-mounted, windshield-mounted or other head-up displays. We have recently demonstrated green TOLEDs using tris(8-hydroxyquinoline) aluminum (Alqg) as the electroluminescent layer. The TOLEDs are >71% transparent when turned off, and emit light from both top and bottom diode surfaces with high efficiency (=1% quantum efficiency) when turned on. In this paper, we present new results on high-efficiency blue TOLEDs. We introduce a novel, highly efficient, double heterostructure TOLED, which permits the use of less stable luminescent molecules which would otherwise be damaged by the electrode deposition, thus greatly increasing the potential range of TOLED colors.