Tuning electron injection/transporting properties of 9,10-diphenylanthracene based electron transporters via optimizing the number of peripheral pyridine for highly efficient fluorescent OLEDs

Abstract

By incorporating different number of pyridine rings to the periphery of the 9,10-diphenylanthracene (DPA) core, four new pyridine-containing DPA derivatives, 3-(4-(10-phenylanthracen-9-yl)phenyl)pyridine (AnPy), 9,10-bis(4-(pyridin-3-yl)phenyl)anthracene (AnDPy), 3,3'-((2-(pyridin-3-yl)anthracene-9,10-diyl)bis(4,1-phenylene))dipyridine (AnTPy), 3,3'-(9,10-bis(4-(pyridin-3-yl)phenyl)anthracene-2,6-diyl)dipyridine (AnFPy) were designed and synthesized as electron transporters. Their photophysical properties, energy levels and electron mobilities can be readily regulated through tuning the quantity of the pyridine ring. Through optimizing electron injection/transporting properties, AnTPy exhibits not only a suitable lowest unoccupied molecular orbital (LUMO) energy level for electron injection into light-emitting layer (EML), but also a relatively high electron mobility of around 10−3 cm2 V−1 s−1, which is about two orders of magnitude higher than that of the widely used material Alq3. As expected, the blue fluorescent OLEDs with AnPy, AnTPy and AnFPy as an electron-transporting layer (ETL) exhibited superior performance compared to that using Alq3, remarkably lowering the driving voltages and improving efficiencies. In particular, the device with AnTPy as an ETL showed a maximum current efficiency of 14.4 cd A−1, a maximum power efficiency of 12.1 lm W−1, a maximum external quantum efficiency (EQE) of 8.15% and low efficiency roll-off even at an illumination-relevant luminance of 10,000 cd m−2. These results clearly demonstrated that tuning electron injection/transporting properties by optimizing the number of peripheral electron-withdrawing groups was an efficient strategy to achieve high-performance ETMs.