Lowest OLEDs

Spiro-FPAl/TPBI/Bphen Cs/Al. A very low operating voltage of 3.4 V at luminance of 1000 cd/m2 was obtained, which is the lowest value reported for either small-molecule or polymer blue electroluminescent devices. Pure blue color with CIE coordinates (0.14, 0.14) have been measured with very high current (4.5 cd/A) and quantum efficiencies (3.0% at 100 cd/m2 at 3.15 V) [245]. In another paper, Spiro-FPA2 (126) was used as a host material with an OLED device structure of ITO/CuPc/NPD/spiro-FPA2 l%TBP/Alq3/LiF that produces a high luminescent efficiency of 4.9 cd/A [246]. 

Fig. 1.20. Schematic energy band diagram of a two-layer organic light emitting diode (OLED), in which tin-doped indium oxide (ITO) is used to inject holes into the highest occupied molecular orbital (HOMO) and a low work function metal to inject electrons into the lowest unoccupied molecular orbital (LUMO)...

In the dark, this reaction is likely to involve ion pairs of the lowest coordination, e.g., MjcOjc, whereas in the presence of UV irradiation other sites are involved, such as 02c. The presence of such ion pairs on the model surface can be seen in Fig. 11. The coordination of the oxygen ion appears to be the dominant feature in determining whether the adsorption is molecular or dissociative. Similar ion sites are probably to be involved in the H2/D2 equilibration reaction, and special configurations such as a triangular array of Ole ions maY play an important role. The increased yield of 02 after adsorption of hydrogen is most likely to arise from electron donation by the —H species, the hydrogen either forms more surface... 

Refer to Eigure 10.2. As shown, the lowest solubility of Ca in equilibrium with CaC03 is at a pH of approximately 9.3. This represents the optimum pH for adding lime or soda ash to precipitate calcium as CaC03. Raising the pH to about 11 practically dissolves all the CaC03. This is illustrated in the reaction below. The anion species responsible for raising the pH to 11 is the OlE. Thus, the chemical reaction is... 

An often harmful effect in conjugated polymers is aggregation via locally enhanced interchain interaction. It depresses the excited-state energy in the dimer/aggregate. If the oscillator strength of the lowest transition is lower than average this causes a prolongation of the fluorescence lifetime and, since nonra-diative channels are not affected, a decrease of the fluorescence efficiency that is detrimental for OLEDs. 

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