A Simple and Effective Way of Achieving Highly Efficient and Thermally Stable Bulk-Heterojunction Polymer Solar Cells Using Amorphous Fullcrene Derivatives as Electron Acceptor

摘要

Polymer solar cells have been considered as a promising alternative for renewable energy because of their potential for low-cost manufacturing.1 Until now, the most efficient solar cell was based on the bulk-heterojunction (BHJ) devices composed of a blend of poly(3-hexylthio-phene) (P3HT) electron donor and [6,6]-phenyl C_(61) butyric acid methyl ester (PC_(61)BM) electron acceptor that showed a power conversion efficiency (PCE) of ~5%. Within the BHJ film, it is critical to control the morphology of the blend to form an interpenetrating network with nanoscale phase separation between the donor and the acceptor at a distance of ~10 nm to maximize exciton dissociation and provide an effective pathway for charge transport and collection. The optimum morphology can be achieved by controlling the kinetics of segregation and crystallization of the components through careful adjustment of the parameters involved in the fabrication processes, such as solvent, blend ratio, thermal annealing, and other post treatment conditions. However, such a phase-separated morphological structure is not very thermodynamically stable because small molecules like PCBM and even polymers like P3HT can still have certain freedom to diffuse slowly or recrystallize over time especially under elevated temperatures. This gradual change in the microstructure will lead to reduced number of interfaces and result in degrading the performance of the device. This is detrimental to the long-term performance of polymer solar cells.