A Systematic Approach to Solvent Selection Based on Cohesive Energy Densities in a Molecular Bulk Heterojunction System

Abstract
The solubilities of 3,6‐bis(5‐(benzofuran‐2‐yl)thiophen‐2‐yl)‐2,5‐bis(2‐ethylhexyl)pyrrolo[3,4‐c]pyrrole‐1,4‐dione (DPP(TBFu)2) and [6,6]‐phenyl‐C71‐butyric acid methyl ester (PC71BM) in a series of solvents are measured, and this data is used to calculate the Hansen solubility parameters of the two materials. The dispersion, polar, and H‐bonding parameters of DPP(TBFu)2 and PC71BM were found to be (19.3, 4.8, 6.3) and (20.2, 5.4, 4.5) MPa1/2, respectively, with an error of ± 0.8 MPa1/2. Based on the solubility properties of the two materials, three new solvents (thiophene, trichloroethylene and carbon disulfide) were utilized for the DPP(TBFu)2:PC71BM system which, after device optimization, led to power conversion efficiencies up to 4.3%.