The Challenge

One new class of OPVs is based on blends of semi-conducting polymers. As the polymers are coated onto the flexible substrates, the molecules self-assemble to form a complex composite material. It has become clear that the performance of the polymer photovoltaic films is very sensitive to variations in the processing conditions in which the devices are made. It is believed that processing conditions influence nanoscale structure and the resulting performance is strongly influenced by the nanoscale structure but in situ measurements of the structural evolution during processing are needed to understand this effect.

The Solution

Real time in situ studies of the changes in morphology during the coating process itself, were monitored with X-ray diffraction techniques using Diamond beamlines I22, I16 and I07. During the experiment, the substrate was coated with the polymer solution and the drying and self-organisation processes were characterised by grazing incidence X-ray diffraction (GIXD) and grazing incidence small angle X-ray scattering (GI-SAXS). Grazing incidence diffraction probes the nanoscale structure of thin films and is ideally suited to the investigation of these complex composite materials.

The Benefits

The experiments allowed the researchers to gain an insight into the mechanism by which the processing conditions can affect the resulting nanoscale structure of the organic photovoltaic films. Understanding the relationship between the processing conditions and the structure will lead to design control of the materials to give the optimum morphology for the most efficient photovoltaic device performance.