Abstract
Organic light-emitting diodes (OLEDs) are attracting increasing interest owing to their promising applications in flat panel displays and solid-state lighting. To make it applicable soon, manufacturing cost is the top priority to be considered. Therefore, this can explain why numerous researches have been paid much effort on design and fabrication of solution process. Nanomarkets estimates that the output value of solution-processable materials is 50 million US dollars in 2013, and will markedly increase to 800 million in 2019, again indicating that the importance of development of solution process. In this report, two different solution processes are employed to fabricate the emissive layers in OLED devices. In the first part, blue and green OLEDs are fabricated via solution process by using a novel phosphorescent material, bis[5-methyl-8-trifluoromethyl-5H-benzo(c) (1,5) naphthyridin-6-one] iridium(picolinate) (3-CF3BNO), which has a short excited-state lifetime (0.39 μs) and a relatively high quantum yield (72 %). Coupled with an appropriate host material, the resultant green OLED shows an efficacy of 52 and 61 lm/W and external quantum efficiency of 18 and 23 % at 100 and 1,000 cd/m2, the highest among all reported solution-processed green OLEDs. In the second part, to overcome the disadvantage of molecular material that is not easy to be used in contact-printing, a method of blending with molecular and polymer host is designed and fabricated to contact-print the emissive layer onto the OLED devices successfully. By using this method, the maximum luminance of fabricated blue, green, red, and white OLEDs is 29,000, 29,000, 4,000, and 18,000 cd/m2, respectively. That contact-printing can be achieved successfully may be attributed to the blended host, which is composed of a polymer host with a good film integrity and a molecular host with a fine electroluminescence character.