Exciplex emission and energy transfer in white light-emitting organic electroluminescent device

We report a white light organic electroluminescent (EL) device achieved through exciplex formation between organic materials as a green color light source. Exciplex formation at 500 nm originated from poly(N-vinylcarbazole) (PVK) and 2,5-bis(5-tert-bytyl-2-benzoxazolyl)thiophene (BBOT), exciplex formation at 550 nm between from N,N′-diphenyl-N,N′-bis(3-metylphenyl)-1,1′-biphenyl-4,4′-diamine (TPD) and BBOT was assumed to correspond to the complex formation covering the green color region. In the mixed emitting materials, the PL decay lifetimes of BBOT and poly(3-hexylthiophene) (P3HT) were increased as much as 35–68 and 1.5–19 ns, respectively. This indicates that the energy transfer occurred from PVK to BBOT and P3HT, enhancing the quantum efficiency of these materials. We achieved white light emission with brightness as great as 12.3 μW/cm2 at 20 V, corresponding to CIE coordinates of x=0.29 and y=0.353. The EL spectrum of the device was changed with a function of the applied voltage.