The critical role of additives in binary halogen-free solvent systems for the general processing of highly efficient organic solar cells

With the rapid progress of organic solar cells (OSCs), avoiding processing with halogenated solvents has become an urgent task for the practical utilization of OSC technology. In this work, a non-halogenated solvent combination of methylbenzene and methylnaphthalene was developed to replace the use of the halogenated binary solvents chlorobenzene and 1-chloronaphthlene. We have systematically studied the effects of the binary solvents on the morphology, charge carrier mobility, and photovoltaic properties. Importantly, we have found that the halogen-free mixture solvent showed a wider applicability to various polymer: fullerene systems than that of the halogenated ones and realized a PCE of over 8% in the PTB7:PC71BM based OSC. Our work demonstrated that the use of the additive strategy for halogen-free solvent systems may provide a feasible route to address the critical environmental issues associated with large-scale manufacturing.