ESEM imaging of polyfluorene blend cross-sections for organic devices

We report the use of environmental scanning electron microscopy (ESEM) to determine the phase separation in the cross-section of a 200 nm thick polyfluorene blend film, of the type used in polymer photovoltaic devices and LEDs. The micron and sub-micron surface phases are found to penetrate through the film to the underlying substrate, whilst smaller surface features do not necessarily propagate through the film. The observed cross-sectional structure helps to explain the optoelectronic response of these blends and shows that ESEM is an effective tool in the characterisation of polymer blend cross-sections. (C) 2002 Elsevier Science B.V. All rights reserved.