Electron blocking layer

PLD has also been utilized to produce bilayer electrolytes. In one study, aNiO-YSZ (anode support, tape cast)/NiO-SDC (AFL, screen-printed)/ScSZ-SDC (electrolyte bilayer, PLD)/SSC (cathode, screen-printed) cell showed excellent performance (0.5 and 0.9 W/cm2 at 550 and 600°C, respectively), with an OCV of 1.04 V at 600°C, indicating that the PLD technique was successful in depositing a sufficiently dense ScSZ electronic blocking layer to suppress electronic conduction normally observed across single-layer SDC electrolytes, and which typically result in lower OCV values (0.87 V, 600°C) [46, 127],... 

Fig. 32 Typical electrophosphorescent multilayer device architecture composed of a hole injection layer (HIL), a hole transport layer (HTL), a emission layer (EL), a hole blocking layer (HBL), an electron blocking layer (EBL), and finally an electron transporting layer (ETL). Shown are the HOMO and LUMO energy levels of the corresponding molecules [77]. The vacuum level is assumed to be constant...

Emissive Layer Electron Blocking Layer Hole Transport Layer... 

The approach to improving the carrier injection outlined in Section 4.4.4 has recently been extended to a multilayer structure with the addition of both an electron injecting (hole-blocking) layer and a hole injecting (electron-blocking) layer see X. Gong et ah, Adv. Mater., 2005, 17, 2053. 

It should be mentioned here that a6T is also used in other multilayer LEDs, e.g. in an ITO/a6T/tetra(tert-buty ) - sexiphenylene/tris(8- hydroxyquinoline)alumin -ium/Mg Ag LED, in which the quinoline acts as emitting layer whereas a6T enhances hole injection and the phenylene acts as an electron blocking layer, confining the electrons in the emitting layer [319]. 

Uchiyama e al. [67,315] used o(,a -dimethyl-anT with n = 4, 5, and 6 on ITO substrates with Al electrodes. The emission for all devices is orange/red. The observed quantum efficiency was 2.6 x 10 for a6T which is very low if compared with the values reported above. Also multilayer devices in which a4T and a5T act as an electron blocking layer and a6T acts as an emitting layer and a hole-transporting layer, were produced, which yielded 115 times and 1230 times higher quantum efficiencies, respectively. 

The monopolar devices with predominantly hole current were constructed by placing a thin Alq layer between NPB layers, which act as hole-transport and electron-blocking layers. The nearly monopolar characteristic of such devices was confirmed by observing only weak electroluminescence, which also precluded using it to evaluate the extent of operational degradation. On the other hand, the differences in absorption spectra of Alq and NPB permitted the separate photoexcitation of the thin Alq layer with 442 nm Hg line. In situ measurements revealed continuously decreasing photoluminescence... 

At the early stage of phosphorescent OLED development, red triplet devices often employed a conventional architecture— HTL, EML, and ETLs were placed between the electrodes. Additionally, a HBL was often inserted between the EML and the ETL. The general structure of a red phosphorescent OLED is shown in Figure 14.30. The device may also include a HIL and an exciton/electron-blocking layer (EBL) placed on the anode side of the EML. The effect of the blocking layers on device performance and criteria for material selection for the layers in triplet OLEDs will be discussed in Section 14.4.2.2. The structures of materials commonly used in red phosphorescent OLEDs are shown in Figure 14.31. 

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