Polymer cell images provide insight

The first high-resolution 3D images to be taken of the inside of a polymer solar cell have provided insights into its nanoscale structure and operational principles.

Researchers from the Eindhoven University of Technology in Holland used 3D electron tomography to visualise the mixing of a polymer and metal-oxide blend. They then passed these images onto the Institute of Stochastics in Ulm, Germany, where they measured the typical distances between the two components and analysed its efficiency.

Writing about their findings online in Nature Materials, the research team said that the quantitative analyses of the structure matched exactly with the recorded performance of the solar cells in sunlight.

This may prove significant to improving the future efficiency of the technology. Currently, polymer solar cells lack the high efficiencies of their silicon counterparts. However, they benefit from being flexible, lightweight and suitable for a wide range of applications.

Their inefficiency is largely due to the different chemical nature of polymers and metal oxides that makes the nanoscale structure difficult to control.

The Eindhoven researchers have overcome this using a precursor compound that only converts the polymers into the metal oxide after it is incorporated in the photoactive layer. According to the researchers, this allows better mixing and enables extracting up to 50 per cent of the absorbed photons as charges in an external circuit.

The researchers hope to use the 3D imaging technique to improve their analysis over the morphology of the photoactive blend and improve the power conversion of the polymer cells even further.