Organic light-emitting diodes with varying thickness of bathocuproine layer

A series of organic light-emitting diodes (OLEDs) with or without a bathocuproine (BCP) layer inserted in the control device indium-tin-oxide (ITO)\ N,N'-bis-(1-naphthl)-diphenyl-1,1'-biphenyl-4,4'-diamine (NPB)\ tris(8-quinolinolato) aluminum (Alq)\LiF\Al have been fabricated and measured. Different influences of the BCP layer on electroluminescence (EL) of the OLEDs have been investigated. It is found that the highest efficiency of the OLED with a 1-nm BCP layer inserted between NPB and Alq increases to 3.99 cd/A, similar to 48% higher than that of the control device, while the EL efficiencies of the devices with other structures are similar to the latter. This phenomenon is ascribed to the hole-blocking effect of the BCP layer and the resulting higher density of carriers in the emission zone of the OLED. The EL performances of the OLEDs with different thicknesses of BCP layer are also discussed in details.