Morphology evolution by controlling solvent-solute interactions using a binary solvent in bulk heterojunction solar cells

Improved power conversion efficiency of poly(indacenodithiophene-co-phananthrene-quinoxaline) (PIDT-PhanQ)/[6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) based bulk- heterojunction (BHJ) solar cells was achieved upon adding tetrahydrofuran (THF) as a co-solvent to 1,2-dichlorobenzene (DCB). This reasonably large enhancement is achieved due to THF changes the morphology in the active layer by reducing the solvent-solute interaction. The Flory-Huggins interaction parameter and cohesive energy densities for PIDT-PhanQ and PD71BM with different solvents were further studied to understand the underlying phase separation mechanism in BHJ films. (C) 2013 AIP Publishing LLC.