Patterns of efficiency and degradation of composite polymer solar cells

Bulk-heterojunction plastic solar cells (PSC) produced from a conjugated polymer, poly(2-methoxy-5-(3′,7′-dimethyloctyl-oxy)-1,4-phenylenevinylene) (MDMO-PPV), and a methanofullerene [6,6]-phenyl C61-butyric acid methyl ester (PCBM) were investigated using photocurrent imaging techniques to determine characteristic patterns of efficiency and degradation. The solar cells with power efficiencies of up to 2.6% showed significant inhomogeneities and variations depending on the preparation steps (e.g. aluminum deposition), suggesting there is still room for improvements. A characteristic feature of the well-known photoinduced and dark cell degradation is the formation of islands of higher efficiency. Degradation mechanisms appear to have a morphological component. The imaging technique will open opportunities for combinatorial plastic solar cell research.