Theoretical Analysis And Experimentalize Of Transparence And Top White Organic Light-emitting Diodes

Transparent white organic light-emitting devices (TWOLEDs) may be applied to automobile windshields, architectural windows, eyewear and special illumination.Transparent white organic light-emitting devices with a LiF/Yb:Ag cathode are reported. The device with a structure of ITO/m-MTDATA(40nm)/NPB(7nm)/rubrene (0.1nm)/NPB(3nm)/TPBI(30nm)/Alq(20nm)/LIF(0.5nm)/Yb:Ag (15nm). shows few differences in luminance and color purity from both sides. For instant, at a driving voltage of 10 V, the luminance and CIE coordinates of 1173/1488 cd/m2 and (0.3482,0.3596)/(0.3508,0.3352) are obtained from top/bottom sides. CIE coordinates of the device from both sides are voltage independent, and the maximum total electroluminescence efficiencies of the device are 4.6 cd/A.The TWOLED with Sm cathode is fabricated. with the structure of ITO/m-MTDATA (30 nm)/NPB (15 nm)/rubrene (0.1 nm)/NPB (4 nm)/TPBI (30 nm)/Alq3 (20 nm)/Sm (30 nm)/Alq3 (50 nm). at a driving voltage of 10 V, the luminance of the device is 1242/667.8 cd/m2 obtained from top/bottom sides. CIE coordinates of the device from both sides are voltage independent, at a driving voltage of 5v the CIE coordinates of both side are (0.2902,0.3045) and (0.3073,0.3157).And at a driving votage of 15v are (0.3007,0.3135) and (0.3134,0.3207). And the maximum total electroluminescence efficiencies of the device are 5 cd/A.Top-emitting organic light-emitting device (TEOLEDs), giving off light through a transparent or semitransparent top electrode, can fabricated on arbitrary substrates and provide a high-aperture-ratio display. High-conductivity and transparent indium tin oxide (ITO) is used for the bottom emitting OLEDs. However, indium is a relatively scarce element and ITO films is the lack of mechanical stability. Thus, ITO-free TEOLEDs will be superior to bottom one.White OLED (WOLED) is of interest due to its application in full-color display or lighting. For lighting applications, in contrast to bottom-emitting WOLED, progress of top-emitting WOLED (TEWOLED) has fallen behind. The key challenge is the microcavity effect presenting in the TEOLEDs with a semitransparent metal top cathode, which leading to narrow EL spectra and angular color non-uniformity that are not beneficial for lighting devices. It can be overcome by applying an light outcoupling layer on top cathode to increases the transmission of the top electrode and reduces the microcavity effects. Besides, high color rendering index (CRI) is also important for the lighting devices, however, there is few reports on a high CRI TEWOLED and no report on the CRI angular characteristics of the TEWOLED.The improvement of the angular dependence characteristics of the device can be attributed to the low reflection and high transmission of the Sm cathode (about 5% and 45% in the visible region). And the CIE coordinates only shifted by (0.008,0.009) from 0 to 30°and shifted by (0.044,0.024) from 0 to 80°.The angular color uniformity of the TEWOLEDs could be imporved by introducing a light outcoupling layer on the top of the cathode.The color shifted only by (0.014,0.018) for MoOx light outcoupling layer from 0 to 60°we optimizated the RGB TEWOLED using Ag anode and LiF/Al/Ag(15 nm) cathode considering the angular color uniformity and the radiated power. A 35-nm MoOx was used as the light outcoupling layer. The device had relatively stable angular color uniformity and the CIE coordinates shifted by (0.027,0.019) from 0 to 60°. The CRI and the correlated color temperature (CCT) in forward direction of the device are 90 and 6750 K, respectively. And the CRI of this device is also less angular dependent. The CRI can reach 83 at viewing angle of 60°. The results indicated that a color-stable and high-CRI TEWOLED could be obtained by carefully desing the structure, and such a device could be used as a white lighting device.For full-color display applications, the combination of WOLED and color filters is a most promising technology. Nevertheless, WOLEDs usually exhibit broad EL spectra and match poorly with the transmission spectra of the color filters [15,16]. Thus, RGB colors filtered from WOLEDs are often less saturated and the color gamut of the display is narrow. Microcavity TEWOLEDs with three narrow emission peaks occurring at desired RGB wavelengths could well matched transmission spectra of RGB color filters to achieve a wide color gamut display, especailly for a near-to-eye display in which angular performance is less important. However, there is few systemic studys to the microcavity effect on the color gamut and color shift of the display basing on TEWOLED A two-peak TEWOLED with LiF/Al(1 nm)/Ag(20 nm)/MoOx (35 nm) as the cathode and Ag (150 nm)/Alq3 (75 nm)/Ag(20 nm)/Alq3 (45 nm)/Ag (20 nm) as anode were performed. we can see the calculated EL spectra and CIE coordinates agree very well with the experimental results. In the calculation, the layer thicknesses were adjusted on the order of a few percent, which is well within the experimental uncertainties.The angular dependence characteristics of such devices could be improved by using a low reflective metal in the MDPC. The CIE coordinates of this device only shift by (±0.013,0.013) from 0 to 80°.The CIE coordinates of this device only shift by (-0.018,0.009) from 0 to 30°. And the spectra of the TEWOLED is well matched the transmission spectra of RGB color filters. TEWOLED gives a greatly enhanced color gamut of 92.3% versus 84.2% of BEWOLED. The results indicated the TEWOLED with a MDPC anode could be a selective light souce for a near-to-eye display, such as headset microdisplay.