Blue Organic Light Emitting Diodes with Graded Junction

A blue organic light emitting diode(OLED) with a graded junction(GJ) at hole transporting layer(HTL) and emitted layer(EML) interface was constructed.Compared with the conventional heterojunction(HJ) OLED,GJ OLED exhibited significantly improved stability,and the half lifetime achieved 6998 h at initial luminance 100 cd/m2,which is more than 6 times longer than that of HJ OLED.And a Gaq thin layer is inserted in the TBADN/Alq interface,the step barrier from Alq Gaq to TBADN for electron injection is though formed.The GJ devices with Gaq layer show 20% higher efficiency than that of conventional and 7 times longer lifetime than that of HJ one.