Polymer 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.

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.

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

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.

The I-V and L-V characteristics of LECs based on m-LPPP do not show the characteristic symmetric shape usually observed in LECs. In contrast to polymer LEDs, the current-voltage (I-V) and the luminance-voltage (L-V) characteristics for LECs, which are not operated in a frozen junction regime (see below) should be fairly symmetric. This holds even for different electrode materials, because... 

Figure 14.21 Eleotroluminesoenoe chemistry and spectrum (top) and (bottom) current density ( ) voltage-luminance (O) characteristics for indium-tin oxide/polymer 3 (above).

The basic structure of a single-layer polymer LED was briefly introduced in Section 1 and is shown in Fig. 29.2. The current-voltage (l-V) and luminance-voltage [L-V) characteristics of a typical ITO/PPV/Ca device are shown in Fig. 29.8. The luminance is approximately proportional to the current, indicating that the quantum efficiency is approximately constant over a wide range of currents. The voltage required to produce a given... 

Before ending this section, the current density-voltage-luminance characteristics of two PLEDs using Ag/Ca (solid symbol) and Ag/Al/CsF (open symbol) as a cathode, respectively, with 40 nm of poly(3,4-ethylene dioxythiophene) (PEDOT) polystyrene sulfonate) (PSS) as a polymer anode and 100 nm of F8BTas a green-emitting layer are depicted in Fig. 5.16. The thickness of the Ca, CsF, A1 and Ag layers is 50, 5, 80 and 100 nm, respectively. The Al/CsF instead of Cs was used as the cathode since the role of A1 on CsF is known to release Cs into the polymer [80], It can be seen that the Ca device shows much larger current density than the CsF/Al device, in contrast to the common belief that the lower work function of... 

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