Luminance-voltage characteristic

The current-voltage and luminance-voltage characteristics of a state of the art polymer LED [3] are shown in Figure 11-2. The luminance of this device is roughly 650 cd/m2 at 4 V and the luminous efficiency can reach 2 lm/W. This luminance is more than adequate for display purposes. For comparison, the luminance of the white display on a color cathode ray tube is about 500 cd/m2l5J. The luminous efficiency, 2 lm/W, is comparable to other emissive electronic display technologies [5], The device structure of this state of the art LED is similar to the first device although a modified polymer and different metallic contacts are used to improve the efficiency and stability of the diode. Reference [2] provides a review of the history of the development of polymer LEDs. 

Figure 11-2. Current-voltage and luminance-voltage characteristics of a stale of the art polymer LED.

FIGURE 10.17. Luminance-voltage characteristics of an LEC fabricated from BDOH-PF blended with PEO and a Li salt. (From Ref. 33.)... 

FIGURE 10.20. EL spectra of a thermally aligned ITO doped-PI PF2/6 Ca LED with the polarizer aligned parallel (filled circles) or perpendicular (open circles) to the rubbing direction. Inset Luminance-voltage characteristics for devices with doped (filled squares) and undoped (open circles) PI layers. (From Ref. 4.)... 

Fig. 4.13. Comparison of pLED on conventional ITO-coated glass substrate with pLED on ITO-free PET substrate, (a) Current density-voltage characteristics, (b) Luminance-voltage characteristics...

Fig. 6.6 Luminance-voltage characteristic for the polymer blend PCzDBT20/MEH-PPV (1/240). Adapted from Niu et al. [26] with permission from Wiley-VCH.

As can be seen from the typical luminance-voltage characteristic presented in Fig. 6.6, light generation requires a minimum voltage, the tum-on voltage, at which light emission commences. 

Figure 8. Luminance-voltage characteristics of polymer/Alq devices, (circles) PTPDES and (triangles) PTPDEK.

Figure 12. Luminance-voltage characteristics of white-light-emitting ITO/dye-dispersed PVK/Mg Ag device.

Figure 12.3 Device characteristics for a polymer light-emitting device showing (a) the current-voltage characteristic (open circles) and the luminance-voltage characteristic (filled squares) and (h) the ahsorhance (Ahs) and photoluminescence (PL) spectra. The electroluminescence is very similar to the PL.

Figure 11. Current-voltage and luminance-voltage characteristics for the IT0/PVK/6P/PPy/Al device. Inset The CIE color coordinates of the EL spectra of the ITO/PVK/6P/PPy/Al device under different applied voltages.

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