A new silole monomer with two 4-(N,N-dimethylamino)phenyl substitutions on silicon atom as designed and synthesized.Three copolymers PF-N-HPS1,PF-N-HPS10 and PF-N-HPS20 were then obtained by copolymerizations of 2,7-fluorene derivatives with the silole monomer at feed ratios of 1%,10%,and 20%.Their UV-vis absorption,electrochemical,photoluminescent,and electroluminescent (EL) properties were investigated.PF-N-HPS possessed HOMO levels of 5.25-5.58 eV,and showed green emissions.Using PF-N-HPS as the emissive layer,three different polymer light-emitting diodes were fabricated as device A with ITO/PEDOT/PF-N-HPS/Al,device B with ITO/PEDOT/PF-N-HPS/Ba/Al,and device C with ITO/PEDOT/PF-N-HPS/TPBI/Ba/Al.For the device A,PF-N-HPS only showed very low EL efficiency of 0.06-0.33 cd/A,indicating that the Al cathode could not inject electron efficiently to the emissive polymers containing the 4-(N,N-dimethylamino)phenyl groups.For the device B,low work function Ba supplied better electron injections,and the EL efficiency could be improved to 0.85-1.44 cd/A.TPBI with a deep HOMO level of 6.2 eV could enhance electron transport and hole blocking.Thus modified recombinations and largely elevated EL efficiency of 4.56-7.96 cd/A were achieved for the device C.The separation of the emissive layer and metal cathode with the TPBI layer may also suppress exciton quenching at the cathode interface.
LIU ZhiTianHU SuJunZHANG LinHuaCHEN JunWuPENG JunBiaoCAO Yong
