White organic electroluminescence from an exciplex based on the novel substituted aluminium quinolate complex

Abstract

A saturated white organic light-emitting device was obtained from an exciplex mechanism by using a novel blue-green fluorescent tris(5-mesitylsulfone-8-hydroxyquinolato)aluminium(III), Al(MSq)₃. Its absorption and photoluminescence appear at 3.25 eV and 2.56 eV. In photoluminescence, an exciplex, generated from an Al(MSq)₃/TPD blend, was found at 2.10 eV. The lifetime of the Al(MSq)₃/TPD blend is 22.3 ns, which is longer than that of either Al(MSq)₃ or TPD. Due to the exciplex formation, the orange light generated can be combined with the blue-green light generated from Al(MSq)₃ to achieve a white light emission. In an optimized electroluminescence device structure of [glass/ITO (200 nm)/PEDOT:PSS (75 nm)/blend (72 nm)/BCP (8 nm)/LiF (1 nm)/Al (200 nm)], the saturated white light emission was observed at Commision Internationale De L'Eclairage (CIE) coordinates of (0.35, 0.34). The EL spectrum of the device is also independent of the applied voltage. Its maximum brightness and efficiency are 26 cd m⁻² at 15.2 V/67 mA cm⁻², and 597 µW A⁻¹ at 12.5 V/28 mA cm⁻², respectively.