Organic light emitting diodes using fluorine doped tin oxide thin films, deposited by chemical spray pyrolysis, as anode

Thin films of tin oxide doped with fluorine (SnO2:F) have been deposited by chemical spray pyrolysis. The SnO2:F thin films are crystallized in the excepted tetragonal structure, with a preferential orientation of their crystallites along the (2 0 0) direction. They exhibit a good transparency in the visible and a small resistivity (ρ = 4.23 × 10−4 Ω cm). These SnO2:F thin films have been used as anode in organic light emitting diodes (OLEDs). These organic devices are based on the bilayer 4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP), which is used as hole transporting layer (HTL) and aluminium (III) tris(8-hydroxyquinoline) (Alq3), which is used as electron transporting layer (ETL) and light emitting layer (EL). It is shown that if the electroluminescent signal of the OLEDs using SnO2:F as anode is smaller than that of OLEDs using indium tin oxide (ITO), this signal is significantly improved when the SnO2:F is covered by an ultra-thin gold film. This improvement can be attributed to a better matching between the work function of the anode and the highest occupied molecular orbital (HOMO) of the HTL, which improves the hole injection efficiency.