Organic light-emitting diodes (OLEDs) are fabricated by using metallophthalocyanine and subphthalocyanine as electron-transport materials. The performance of the electroluminescence in the device ITO/CoPc/NPB/Alq<sub>3</sub>/TPBi/Pcs/Mg: Ag is systematically investigated. The turn-on voltage, maximum luminance and maximum current efficiency of the device with a SnPc electron-transport layer can reach 7.6 V, 7550 cd/m<sup>2</sup> and 3.26 cd/A, respectively. Meanwhile, the turn-on voltage, maximum luminance and maximum current efficiency of the device with a SubPc layer are 5.4 V, 10059 cd/m<sup>2</sup>, and 6.4 cd/A. The results demonstrate that a relatively unique feature of Subphthalocyaninethe, which could transport electron effectively, and tell us that central metal atoms determined the electron-transport ability of metallophthalocyanine.
We fabricated white organic light-emitting devices (WOLEDs) based on three different configurations for yellow emissive layer (Y-EML), using phosphorescent yellow bis[2-(4-tert-butylphenyl)benzothiazolato-N,C<sup>2</sup>’]iridium (acetylacetonate) [(t-bt)<sub>2</sub>Ir(acac)]. The Y-EML was formed as undoped ultrathin layer, doped ultrathin layer with low (tbt) <sub>2</sub>Ir(acac) concentration and doped thin layer with the same amount of (t-bt)<sub>2</sub>Ir(acac) molecular as the undoped YEML. The results showed that the difference in configurations of the Y-EML affected not only the operating voltage but also the luminance and efficiency characteristics of the devices. Comparing device performance, it was found that devices based on the doped Y-EML showed low efficiency and yellow-dominated light emission, due to triplet exciton
hopping caused by different triplet energy. On the other hand, a device with the undoped Y-EML demonstrated the highest efficiency (79.0 cd/A at 1 550 cd/m<sup>2</sup> and 40.5 lm/W at 1 000 cd/m<sup>2</sup>), attributing to well confined charge carriers and excitons.
White organic light-emitting devices (WOLEDs) based on a double-emitting layer (EML) structure were fabricated, while phosphorescent blue and yellow emitters were employed. An ultra-thin layer of non-doped green tris(2-phenylpyridine) iridium [Ir(ppy)<sub>3</sub>], which was considered as delta-doping layer, was inserted between the two EMLs for optimization. Furthermore, effect of adjusting thickness of this thin layer on device performance was studied. The results showed that the optimized WOLED consisting of 1-nm Ir(ppy)<sub>3</sub> EML achieved a maximum luminance of 29,100 cd/m<sup>2</sup>, maximum external quantum efficiency of 7%, maximum current efficiency of 25.3 cd/A and maximum power efficiency of 7.8 lm/W, together with low efficiency roll-off over a wide luminance range. Meanwhile, the white emission with Commission Internationale del’Eclariage (CIE) coordinates of (0.382,0.446) at a driving voltage of 10 V were observed. The performance enhancement is ascribed to improved charge carrier balance through introduction the highly efficient Ir(ppy)<sub>3</sub> as the thin delta-doping layer.