Computations Improve Blue OLED Performance

When it comes to organic light-emitting diodes used in display and lighting technologies, blue light remains a challenge: Fluorescence-based blue OLEDs are inefficient, and metal-doped phosphorescence-based versions are expensive to make. In 2012, Chihaya Adachi and coworkers at Kyushu University, in Japan, developed a new type of fluorescent OLED that is cheaper. But the efficiency of the device has a tendency to decrease at high current densities. By using computational methods to predict the relevant energy levels of charge-transfer molecules, the same team has now designed molecules that can be used to construct lower-cost blue OLEDs. These OLEDs have efficiencies that rival those of phosphorescence-based devices without suffering from efficiency “roll-off” (Nat. Photonics 2014, DOI: 10.1038/nphoton.2014.12). The molecules are bent in a way that stabilizes the structure needed for efficient fluorescence. The best blue-emitting molecule is made of a diphenylsulfone acceptor connected to two dihydroacridine donors (shown). An OLED device incorporating the compound has an overall efficiency of 19.5%, which is similar to that of phosphorescence-based devices.