Blue light emitting diodes with bathocuproine layer

Several hole transport molecules (N,N′-diphenyl-N,N′-(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine; 4,4-bis[N-(1-naphthyl)-N-phenylamino]biphenyl; 4,4′,4″-tris[N-(1-naphthyl)-N-phenylamino]triphenylamine (TNATA); MTDATA) are blue light emitters [SPIE 3797 (1999) 120]. Realisation of monolayer structures is very easy but their performances are too weak. To improve them, we have built some multilayer structures with electron transport layer (tris(8-hydroxyquinolinate) aluminium (Alq3); bis(10-hydroxybenzo(h)quinolinate) beryllium (Bebq2)) and a bathocuproine (BCP) layer to confine the radiative recombinations in the hole transport layer. To improve hole injection, we inserted poly(3,4-ethylenedioxythiophene) (PEDOT) layer between the indium–tin-oxide anode and the hole transporting layer. The best results are obtained with the four-layer structure PEDOT/TNATA/BCP/Bebq2 (λ=508 nm), luminance=5500 cd/m2 at 10.2 V.