French research group changes polymer molecular structure to improve PV properties

The French National Center for Scientific Research (CNRS), the Institute of Chemistry and Processes for Energy, Environment and Health (ICPEES), and the Institute of Physics and Chemistry of Materials of Strasbourg (IPCMS), have cooperated with French research company, Icube to improve the PV properties of a semiconductor polymer, by changing its molecular structure.

In a study, published in the Journal of Materials Chemistry, the scientists claim they have been able to achieve an efficiency of more than 10% for an organic cell by using their innovation.

In their research, the scientists have shown the subtle links that exist between the molecular structure of one of the essential constituents of the active layer – a fluorinated electron donor polymer – and the conversion efficiency of the organic PV cell.

The authors of the study found that two essential parameters contribute to the efficiency of the cell: The systematic variation of the proportion of fluorine atoms on the polymer backbone; and the length and bulk of the aliphatic chains.

The study has confirmed that the presence of fluorine atoms increases the cohesion between the polymer chains, and promotes the transport of charges between the polymer “boards”. It has also demonstrated that the aliphatic chains, when they increase, a fraction of the “polymer boards” is oriented flat on the substrate, thus promoting the charge transport perpendicular to the substrate.

The research group now intends to extend its analysis to all kind of polymers used in organic solar cells. The goal is to establish more universal macromolecular engineering rules to design even more efficient PV polymers.