Energy transfer between host and dopant molecules in blue organic light-emitting devices

Blue organic light-emitting devices were fabricated with an activator of 4,4′-bis(9-ethyl-3-carbazovinylene)-1,1′-biphenyl doped into the various host materials such as N,N′-bis-(1-naphtyl)-N,N′-diphenyl-1,1-biphenyl-4,4′-diamine; 4,4′-bis(2,2′-diphenylyinyl)-1,1′-biphenyl; 2-methyl-9,10-di(2-naphthyl) anthracene; and 1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene to investigate optical properties of blue light emission in the host-dopant system. By spectroscopic analysis based on multi-peak fits to the emission spectra, we found that energy transfer between the host and dopant molecules have a strong correlation with key features; current density, luminous efficiency, and color index for the devices. Among the present dopant-host systems, the TPBi molecule was found to be the best molecule as a host material for our devices. In contrast, the DPVBi host induced a complex excimer (electromer) leading to a shoulder spectrum with a longer wavelength emission. It was found that the electromer significantly affects the optical and electrical properties of the device.