Stability of the interface between indium-tin-oxide and poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) in polymer light-emitting diodes

A cause for degradation of polymer light-emitting diodes is the oxidation o f the polymer by oxygen diffusing out of the indium-tin-oxide (ITO) anode. This problem can be solved by the introduction of an organic hole-injecting film, poly-(3,4-ethylenedioxythiophene) (PEDOT) doped with poly(styrenesul fonate) (PSS), between the ITO and the emissive polymer. Indeed, a dramatic improvement of the lifetime and also the luminous efficiency has been obse rved. However, our Rutherford backscattering (RBS) studies show that the IT O/PEDOT:PSS interface is not stable. In as prepared glass/ITO/PEDOT:PSS sam ples 0.02 at. % indium was found in the PEDOT:PSS film. Annealing in a nitr ogen atmosphere at 100 degrees C during 2500 h increased the indium concent ration to 0.2 at. %. Upon exposure to air much faster degradation of the IT O/PEDOT:PSS interface was observed; after several days in air the amount of indium reached a saturation concentration of 1.2 at. %. The degradation of the interface can be explained by etching of the ITO due to the strong aci dic nature of PEDOT:PSS. (C) 2000 American Institute of Physics. [S0003-695 1(00)05040-3].