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 (rho = 4.23 x 10(-4) Omega 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 (111) tris(8-hydroxyquinoline) (Alq(3)), 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. (C) 2008 Elsevier B.V. All rights reserved.