Enhanced brightness and efficiency in organic light-emitting diodes using SiO2 as buffer layer and electron-blocking layer

A novel device structure was fabricated with an inorganic SiO2 layer inserted between hole-transporting and electron-transporting layer. In device indium-tin oxide (ITO)/poly [2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylenevinylene](MEH-PPV)/tris-(8-hydroxyquinoline) aluminum (Alq3)/Al, the recombination zone lies in MEH-PPV layer, but in ITO/MEH-PPV/SiO2/ Alq3/Al (device A), the recombination zone moves to Alq3 layers. In another device ITO/N,N′-bis-(1-naphthyl)-N, N′-diphenyl-1,1′-biphenyl-4-4′-diamine (NPB)/Alq3/LiF/Al, the brightness and efficiency were enhanced by inserting SiO2 between NPB and Alq3 layers, and it results from an improved balance of holes and electrons. Our experimental results demonstrate that the SiO2 layer acts as not only a buffer layer but also an electron-blocking layer in these devices.