High-efficiency and color stable blue-light-emitting polymers and devices

Novel fluorene-based blue-light-emitting copolymers with an ultraviolet-blue-light (UV-blue-light) emitting host and a blue-light emitting component, 4-N,N-diphenylaminostilbene (DPS) have been designed and synthesized by using the palladium-catalyzed Suzuki coupling reaction. It was found that both copolymers poly [2,7-(9,9-dioctylfluorene)-alt-1,3-(5-carbazolphenylene)] (PFCz) DPS1 and PFCz-DPS1-OXD show pure blue-light emission even with only 1% DPS units because of the efficient energy transfer from the UV-blue-light emitting PFCz segments to the blue-light-emitting DPS units. Moreover, because of the efficient energy transfer/charge trapping in these copolymers, PFCz-DPS1 and PFCz-DPS1-OXD show excellent device performance with a very stable pure blue-light emission. By using a neutral surfactant poly[9,9-bis(6′- (diethanolamino)-hexyl)-fluorene] (PFN-OH) as the electron injection layer, the device based on PFCz-DPS1-OXD5 with the configuration of ITO/PEDOT:PSS/PVK/ polymer/PFN-OH/Al showed a maximum quantum efficiency of 2.83 % and a maximum luminous efficiency of 2.50 cd A^-1. Its CIE 1931 chromaticity coordinates of (0.156, 0.080) match very well with the NTSC standard blue pixel coordinates of (0.14, 0.08). These results indicate that this kind of dopant/host copolymer could be a promising candidate for blue-light-emitting polymers with high efficiency, good color purity, and excellent color stability.