Blue-green, orange, and white organic light-emitting diodes based on exciplex electroluminescence of an oligoquinoline acceptor and different hole-transport materials

Exciplex electroluminescence colors ranging from blue-green to yellow-orange to white were observed in blends and bilayers of a blue light-emitting oligoquinoline acceptor, 6,6'-bis(2-4-diphenylquinoline) (B1PPQ), and different arylamine donors with varying ionization potential (IP) values. The blend composition is shown to be an effective tool to tune the exciplex electroluminescence colors for a given donor/acceptor (D/A) pair. In the D/A blends, exciplex emission was observed under both optical and electrical excitation. However, in the D/A bilayers, exciplex emission was observed only under electrical excitation, highlighting the critical role of the electron-hole capture at the D/A interface in the exciplex formation. Yellow (CIE = 0.41, 0.52) to orange (CIE = 0.57, 0.42) exciplex electroluminescence was achieved from binary blends of B1PPQ and an arylamine donor with an IP of 5.0 eV. Bilayers of B1PPQ with the same donor gave white electroluminescence colors (CIE = 0.35, 0.32) because of the contribution of both bulk (blue) and exciplex (orange) emissions. Blue-green electroluminescence colors (CIE = 0.16, 0.34) were observed in both blends and bilayers of B1PPQ and a donor with an IP of 5.3 eV. In the D/A bilayer diodes, the competing bulk and exciplex emissions were highly sensitive to the acceptor film thickness and the applied voltage. These results reveal the complex charge-transfer excited-state dynamics at D/A interfaces frequently encountered in multicomponent organic light-emitting diodes.