摘要
Fluorinated non-fullerene acceptors(NFAs) usually have planar backbone and a higher tendency to crystallize compared to their non-fluorinated counterparts, which leads to enhanced charge mobility in organic solar cells(OSCs). However, this selforganization behavior may result in excessive phase separation with electron donors and thereby deteriorate device efficiency.Herein, we demonstrate an effective approach to tune the molecular organization of a fluorinated NFA(INPIC-4 F), and its phase separation with the donor PBDB-T, by varying the casting solvent. A prolonged film drying time encourages the crystallization of INPIC-4 F into spherulites and consequently results in excessive phase separation, leading to a low device power conversion efficiency(PCE) of 8.1%. Contrarily, a drying time leads to fine mixed domains with inefficient charge transport properties,resulting in a moderate device PCE of 11.4%. An intermediate film drying time results in the formation of face-on π-π stacked PBDB-T and INPIC-4 F domains with continuous phase-separated networks, which facilitates light absorption, exciton dissociation as well as balanced charge transport towards the electrode, and achieves a remarkable PCE of 13.1%. This work provides a rational guide for optimizing the molecular ordering of NFAs and electron donors for high device efficiency.
Fluorinated non-fullerene acceptors(NFAs) usually have planar backbone and a higher tendency to crystallize compared to their non-fluorinated counterparts, which leads to enhanced charge mobility in organic solar cells(OSCs). However, this selforganization behavior may result in excessive phase separation with electron donors and thereby deteriorate device efficiency.Herein, we demonstrate an effective approach to tune the molecular organization of a fluorinated NFA(INPIC-4 F), and its phase separation with the donor PBDB-T, by varying the casting solvent. A prolonged film drying time encourages the crystallization of INPIC-4 F into spherulites and consequently results in excessive phase separation, leading to a low device power conversion efficiency(PCE) of 8.1%. Contrarily, a drying time leads to fine mixed domains with inefficient charge transport properties,resulting in a moderate device PCE of 11.4%. An intermediate film drying time results in the formation of face-on π-π stacked PBDB-T and INPIC-4 F domains with continuous phase-separated networks, which facilitates light absorption, exciton dissociation as well as balanced charge transport towards the electrode, and achieves a remarkable PCE of 13.1%. This work provides a rational guide for optimizing the molecular ordering of NFAs and electron donors for high device efficiency.
基金
supported by the Natural Science Foundation of Hubei Province(2018CFA055)
the National Natural Science Foundation of China(21774097,21504065,51573077,21875111)
the Fundamental Research Funds For the Central Universities(WUT:195201017,2019IVB081)
U.K.EPSRC for funding High Resolution Mapping of Performance and Degradation Mechanisms in Printable Photovoltaic Devices(EP/M025020/1)
EPSRC for funding a studentship for E.L.K.Spooner via the Centre for Doctoral Training in New and Sustainable PV(EP/L01551X/1)