High Efficiency Of Non-doped Blue Fluorescent Organic Light-emitting Diodes

Organic light-emitting diodes （OLEDs） have been widely investigated for theirpotential application in full-color flat panel display and solid state lighting. Recently, thediodes with phosphorescent materials of green and red have been widely used in our life.However, the blue-light emitting materials with high efficiency and stable performance arestill rare. The blue diodes with high-efficiency and stable performance are important tofull-color display and solid state lighting. In this paper we fabricate a series of non-doped bluefluorescent OLEDs based on DOPPP as a non-doped fluorescent blue-light emitter andmodifying the thickness of light-emitting layer or the materials of other layers. We mainresearch that how the EL properties of these diodes influenced by different carrier transportlayers and the thickness of light-emitting layer.The non-doped blue fluorescent OLEDs with a configuration of ITO/HIL/NPB/DOPPP/Alq3/LiF/Al have been fabricated. The HIL instead of MoO3、2T-NATA and m-MTDATArespectively. The current efficiency of the device with MoO3is the highes（t4.81cd/A）and theturn on voltage（5.6V）is the lowest. The thin-layer of MoO3reduces the turn on voltage andimproves the efficiency. In addition, we chose TCTA and NPB/TCTA to instead of HIL. Theturn on voltage of the device with TCTA is4.8V，the highest power efficiency is1.95lm/W, itis1.67times than device with NPB. The CIE coordinates of the device with NPB/TCTA,changing from (0.166,0.195) to (0.171,0.207) along with the luminance from75cd/m2to9889cd/m2, the difference just (0.005,0.012). Furthermore, we use TPBi/Alq3as doubleHTL instead of Alq3base on NPB/TCTA as double HIL. Keep the color purity and improvethe stability of the blue diodes.We fabricate the non-doped blue fluorescent OLEDs with thin light-emitting layer basedon DOPPP (the thickness is0.5nm,1nm and2nm respectively), the configuration isITO/MoO3/TCTA/DOPPP/TPBi/LiF/Al. The color-coordinate of the diodes are close to thedeep-blue region by decrease the thickness of DOPPP. Compare to the device with thethickness of DOPPP is20nm，the wavelengths of emission peak of the device with thinlight-emitting layer are blue-shifted8nm with the deep-blue color coordinate of (0.150, 0.148). In addition, we use NPB/TCTA instead of TCTA as double HTL, we achieve a peakcurrent efficiency of3.64cd/A which is1.4times than device with TCTA. The CIEcoordinates of the device with NPB/TCTA，changing from (0.151,0.151) to (0.151,0.144)along with the luminance from26cd/m2to5991cd/m2, the difference just (0.002,0.006).Theresults indicate that double transport layers probably a key factor that accounts for their goodstable performance in color.