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 <i>o</i>-xylene (<i>o</i>-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 <i>o</i>-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