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The performance of a blue polymer light-emitting diodes (PLED) was significantly improved by doping a controlled amount (1%) of a hole transport molecule N,N-bis-(1-naphthyl)-N,N-diphenyl-1,1biphenyl-4,4-diamine (NPB) into the emitting layer. Hole carrier mobility of the blue emitting polymer, BP105 (trade name of The Dow Chemicals Co.), increased from5.27 10 -7 cm -2 /Vs of the pristine BP105 to 1.80 10 -6 cm -2 /Vs with the addition of 1% NPB in BP105. The enhanced carrier mobility greatly promoted performance of a blue PLED device with a device structure of ITO/PEDOT:PSS/BP105+x% NPB/LiF/Ca/Al.Luminanceincreased from573 cd/m 2 to 2,720 cd/m 2 at6Vand efficiencyincreased from 1.1lm/Wto1.6lm/Wat1,000cd/m 2 with1%NPBinBP105.Themostimportantimprovementwasanincrease in the lifetime of the blue device from 80 to 120 hours at an initial luminance of 400 cd/m 2 .W e found that by choosing the appropriate dopant with goodenergy alignment and controlled dopant concentration, the performance of a blue PLED device could be greatly improved. |
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