Abstract
This study involves polyspirofluorenes (sPF) modified by incorporation of charge transporting moieties on side-chain and chain-end to facilitate hole and electron injections. We investigate their electroluminescence behaviors with and without doping with orange fluorescent and red phosphor small molecules as the guest to obtain white and red emission devices. Three parts are included in this thesis. Firstly, by incorporation of triphenylamine (as hole receiver) and carbazole (as transporting bridge) as side-chain of sPF to yield TPA-Cz-sPF, balanced bipolar fluxes and charge mobilities can be realized. By using TPA-Cz-sPF as host material and (5,6,11,12)-Tetraphenylnaphthacene (rubrene) as guest material, single layer white emission LED is obtained having high efficiency of 21.07 cd/A (8.96%), and high luminance of 17,431 cd/m2. The present efficiency is the highest among reported white PLEDs. Secondly, we further modify sPF by incorporation of TPA and Cz on the same side-chain and of electron deficient 3-(4-phenyl)-4-phenyl-5-(4-tert-butylbenzene)-1,2,4-triazole (TAZ) group on polymer chain-end. The designed polymer exhibits improved bipolar injection transport capabilities and deeper blue emission as compared to that without chain-end modification. Single layer LED based on 50GsPF-end-TAZ achieves high efficiency of 6.08%, high luminance of 10,131 cd/m2, and deep blue emission with CIE (1.161, 0.052), revealing the present molecular design is a powerful methodology. Thirdly, We utilize the deep blue polymer 50GsPF-end-TAZ as host material, and dope with 2wt% red small molecule Bis(1-phenylisoquinoline) (acetylacetonate)iridium(III) (Ir(piq)2(acac)). Its single layer LED achieves high efficiency of 9.92% (12.06 cd/A), high luminance of 6,372 cd/m2, and red emission with CIE (0.67, 0.33) which is very closely to 1931 Commission International de l’Eclairage coordinate (CIEx,y 1931) saturation red light.