Current density-voltage-brightness

FIGURE 10. Current density-voltage-brightness (J-B-V) relationships for devices... 

The cathode emits electrons that are accelerated towards the anode with a defined voltage, typically 50-30,000 V. There are basically two types of electrodes thermionic cathodes (tungsten or LaBs (lanthanum hexaboride)) and field emission cathodes. The Wehnelt cylinder controls the current density and brightness of the electron beam. Brightness is defined as current per unit area normal to the given direction, per unit solid angle, and a criterion for beam quality. 

Fig. 4.30 shows the 1931 CIE chromaticity diagram, with coordinates corresponding to the emission from electrophosphorescent PLEDs data points are shown for devices (open circles) biased at different current densities. In Fig. 4.30, the dotted line indicates different color temperatures the dotted oval indicates the approximate area where the human eye perceives the color as white. The CIE coordinates for the Ir(HFP)3 PFO-F(l%) PFO devices are (0.352, 0.388) at J = 1 mA/cm2, very close to the CIE coordinates for pure white light, (0.333, 0.333). The CIE coordinates show only minor shifts at different J. The stability of the CIE coordinates as a function of the brightness and applied voltage is much better than reported previously for PLEDs/OLEDs [11, 50-55]. 

Fig. 11.13 Brightness ( ) and current density ( ) characteristics of a ITO/PEDOT/[lr(DPF)3] PVK-PBD/Ca/Ag device with a lr(DPF)3 concentration of 1 wt.% as function of applied voltage [59].

While polyphenylsilane (1) and poly(l-methyl-2-phenyldisilane) (2) rather deteriorate the diode behavior polyaminophenylsilane (3) strongly reduces the onset voltage of the devices and more than doubles the power efficiency and brightness compared to the single-layer LEDs. (Figs. 2, 3) These results compare favorably to the data Kido et al. reported for double-layer devices using Alqs as emissive layer and polymethylphenylsilane (PMPS) as HTL [2]. In this case a luminescence of 115 cd/m was measured at a current of 10 mA. For the device Al/Alqs/polyaminophenylsilane/lTO, 130 cd/m were obtained at the same current density. 

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