ORGANIC PHOTODIODES ON PRINTED ITO COATINGS

Abstract

We describe the fabrication and characterization of organic photodiodes on solution cast ITO (tin doped indium oxide) bottom electrodes. ITO coatings were produced by gravure printing process on PET and PEN substrates. The sheet resistance could be decreased by heat treatment at 120°C under forming gas atmosphere ( N 2/ H 2) to 1.5 kΩ. The transmission of the ITO coated PET and PEN substrates is more than 80% in the visible range. The printed films were hardened under UV-irradiation at low temperatures (< 130°C) and used as the bottom electrode of an organic photodiode (OPD), consisting of a stacked layer of copper phthalocyanine ( p -type material), perylene tetracarboxylic bisbenzimidazole ( n -type material) and Aluminium tris(8-hydroxyquinoline). The performance of the photodiodes with printed ITO on plastic substrates could be improved by adding a smoothing layer of PEDOT/PSS (Baytron® P) on the ITO coated films and was then similar to the performance of photodiodes with semi-transparent gold as anode. These results demonstrate the suitability of the printed ITO layers as bottom electrode for organic photodiodes. Furthermore the influence of different treatments (forming gas and oxygen plasma treatment) of the ITO bottom electrode on the current-voltage characteristics of the OPDs was studied.