Thermal Annealing Effect on Active Layer Structure in All-Polymer Organic Solar Cells

Abstract

The structural evolution of the components for the active layers of all-polymer solar cells was studied by DSC, X-ray diffraction and optical microscopy. It was found that polymer donor (PTQ1) and polymer acceptor (PNDIT2) form lamellar structures with layers oriented parallel and perpendicular to the substrate, respectively. All films reveal π-π stacking in the direction normal to the film. During thermal annealing the structure improvement occurs only for the donor component. In a PTQ1/ PNDIT2 blend, two components form individual lamellar phases with the texture similar to that of the pure polymers. Upon annealing, the structure of PNDIT2 was found to be disturbed whereas the structure of PTQ1 phase improves. The micro-phase separation occurring during annealing of the PTQ1/ PNDIT2 blend is accompanied by the formation of large spherulitic objects.