Highly Efficient and Operational Stability Polymer Solar Cells Employing Nonhalogenated Solvents and Additives.

The power conversion efficiencies (PCEs) of potential polymer solar cells have been shown to rapidly exceed 15%. However, these high-performance devices are based on halogenated solvents that pose a significant hazard to the atmospheric environment and human beings. The use of nonhalogenated solvents makes the device less efficient because of its solubility issues. In this work, we report high-efficiency devices utilizing PffBT4T-2OD and [6,6]-phenyl C71 butyric acid methyl ester system from nonhalogenated solvents such as o-xylene ( o-XY) and 1-methylnaphthalene (Me) hydrocarbon solvent. When Me was used as the additive, the PCE of prepared devices improved from 1.83 to 10.13%, which is rather higher than that of the devices processed with traditional solvents combined with chlorobenzene and 1,8-diiodooctane (8.18%). Both atomic force microscopy and transmission electron microscopy confirmed that after nonhalogen solvents are treated, a more finely phase-separated dense morphology of active layers than after halogen solvents. At the same time, grazing incident wide-angle X-ray scattering patterns show that the combination of nonhalogenated solvents o-XY and Me ingeniously formed an ordered crystal and π-π stacking. Also, the stability of devices prepared from nonhalogenated solvents was significantly better than that of halogenated solvents under continuous illumination in the air without encapsulation.