Organic Light Emitting Diodes Based on Novel Zn and Al Complexes

Abstract

Organic light emitting diodes (OLEDs) have gained great interest in the last years due to their potential for future flat panel display and solid state lighting applications. OLEDs are a novel and very attractive class of solid-state light sources, which generate a diffuse, nonglaring illumination with high color rendering. Compared to the other major lighting technologies in the market – incandescent, fluorescent, high intensity discharge (HID) lamps, LED and electroluminescent, OLED technology has the potential of achieving substantial energy and CO2 savings, without compromising color rendering or switching speed. The unique features of OLED lighting are inspired the imagination of designers who are exploring various OLED applications: windows, curtains, automotive light, decorative lighting and wall papers. The OLED technology is now being commercialized as a multibillion dollar market. OLEDs are already used in small displays in cellular phones, car stereos, digital cameras, etc. The rapidly growing market for OLED displays and lighting is driving research in both advanced materials and improved manufacturing processes. In spite of the spectacular results achieved, there are still many problems concerning the efficiency, stability and lifetime of OLEDs, materials selection and optimization, encapsulation, uniformity over large areas, manufacturing cost, colour saturation, etc. to be solved. OLED represents a quite complicated system of many very thin layers of various materials situated between electrode layers (one of which is transparent); this system emits light when placed under electric potential. The type of material used as the light emitter determines the specific characteristics of such devices. Two types of OLEDs are developed – on the bases of “small” molecules (SM-OLED) (Tang & VanSlyke, 1987) and conjugated polymers (PLED) (Burroughes et al., 1990), oligomers, etc. Potential emitters for SM-OLED are metal complexes from the lanthanide and platinum groups as well as complexes of Al, Zn, Cd, Cu, Be, B with carefully selected ligands from the group of heterocyclic compounds like as hydroxyquinoline, benzoxazole, benzothiazole, triarylamines, etc. (Petrova & Tomova, 2009). The first generation of efficient devices, pioneered by Tang and Van Slyke from Eastman Kodak (1987), was based on fluorescent