Towards anode with low indium content as effective anode in organic solar cells

In₂O₃ thin films (100 nm thick) have been deposited by reactive evaporation of indium, in an oxygen partial atmosphere. Conductive (σ = 3.5 × 10³ S/cm) and transparent films are obtained using the following experimental conditions: oxygen partial pressure = 1 × 10⁻¹ Pa, substrate temperature = 300 °C and deposition rate = 0.02 nm/s. Layers of this In₂O₃ thick of 5 nm have been introduced in AZO/In₂O₃ and FTO/In₂O₃ multilayer anode structures. The performances of organic photovoltaic cells, based on the couple CuPc/C₆₀, are studied using the anode as parameter. In addition to these bilayers, other structures have been used as anode: AZO, FTO, AZO/In₂O₃/MoO₃, FTO/In₂O₃/MoO₃ and FTO/MoO₃. It is shown that the use of the In₂O₃ film in the bilayer structures improves significantly the cell performances. However the open circuit voltage is quite small while better efficiencies are achieved when MoO₃ is present. These results are discussed in the light of surface roughness and surface work function of the different anodes.