Effect of processing additive on the nanomorphology of a bulk heterojunction material

Abstract

The bulk heterojunction (BHJ) material Si-PDTBT:PC70BM is sensitive to the use of a small amount of 1-chloronaphthalene (CN) as a processing additive; CN as a cosolvent (e.g., 4% in chlorobenzene) causes in a factor of 2 increase in the power conversion efficiency of BHJ solar cells.1 The morphology of the BHJ material, prepared with and without the CN additive is studied with top down transmission electron microscopy, cross-sectional transmission electron microscopy, and atomic force microscopy. The improved performance is the result of changes in the nanoscale morphology. Field-effect transistor measurements are consistent with the observed changes in morphology.