Dark spot formation relative to ITO surface roughness for polyfluorene devices
The failure behaviors of ITO/PEDOT;PSS/polyfluorene/Al devices are different depending on the surface roughness of the sputtered ITO anode film. The spikes on ITO surface are responsible for the initial local shorts of the device, which develop into dark spots very quickly. Indium adsorption is observed on the polymer and Al cathode interface. A chemical etching procedure is used to smoothen the ITO surface without changing the ITO thickness and the sheet resistance. Devices made out of smooth ITO show minimum changes at polymer-cathode interface during operation.