tailieunhanh - Organic Light Emitting Diode Part 8

Tham khảo tài liệu 'organic light emitting diode part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | High-Contrast OLEDs with High-Efficiency 133 ill .G ị Ị Pd Co I I Pt. TeO I I NiFe SSteel s Mo I IA . .X Nk I ậAu Cu Inconel .TiW Nb n5 Ac .c . T I TiN Ị a-GaAs 1 X nfc ITO ZZZ7 2 3 Refractive Index n Fig. 6. Refractive indices and extinction coefficients both given at a wavelength of 550 nm of several metals and semiconductor materials as found in the literature. Some isovaluecurves of nk product are shown most optical constants values are extracted from Palik 1985 and from . Woollam WVASE software 2009 . As shown in Fig. 1 the combination of good AR coating and small microcavity effect apparently lead to a contradiction of the anode s role it must have simultaneously a low external reflectance when seen from the substrate and a relatively large internal reflectance when seen from the cavity layers. It has been observed for a long time in thin-film optics that a thin layer of a material with a large extinction coefficient k can lead to the kind of asymmetric reflectance Goos 1937 . In our design such a layer has thus to be introduced on the anode side of the OLED structure. Of course a compromise must still be made between low reflectance and high emission. Also a too-high microcavity effect is usually not desirable in display application since it leads to a large dependence of the emission on the angle of view. The key to our design is the asymmetry of the anode internal and external reflection. 134 Organic Light Emitting Diode a new anode 500 nm Mg Ag 50 nm Alq3 45 nm NPB Í10 nm Au nm Ag nm ITO nm Inconel nm TiO2 Glass Distance from cathode nm Wavelength nm Fig. 7. a OLED design b calculated reflectance solid line with the photopic curve dash line and the value of the luminous reflectance RD c refractive index profile step and irradiance profile inside the OLED with the arrows showing the metal layers and the emitting layer marked in black. 5. Choice of Materials Diode consideration The selection of materials composing the OLED