Optimized phase separation in low-bandgap polymer:fullerene bulk heterojunction solar cells with criteria of solvent additives

The correlation between the type of solvent additives with specific criteria such as aromatic additives (AAs) and non-aromatic additives (NAAs) and phase separation in the bulk heterojunction (BHJ) films is investigated. By strong interaction between NAAs and non-aromatic segment of polymers, a well-phase separated BHJ morphology with the finer fibrils is developed, thereby leading to balanced charge mobilities and a reduced charge recombination in BHJ solar cells.471