Over 17.5% efficiency ternary organic solar cells with enhanced photon utilization via a medium band gap non-fullerene acceptor

作者：Cao, Congcong; Lai, Hanjian; Chen, Hui; Zhu, Yulin; Pu, Mingrui; Zheng, Nan; He, Feng^*

来源：Journal of Materials Chemistry A, 2021, 9(30): 16418-16426.

DOI：10.1039/d1ta04454k

• PERFORMANCE
• ENABLES

The light harvesting and photocurrent generation from acceptors largely determine the photovoltaic performance of organic solar cells (OSCs). We have designed and prepared two medium band gap non-fullerene acceptors (NFAs), BTIC-EH-2ThBr and BTIC-BO-2ThBr, containing end groups with low electron affinity. The absorption spectrum and the energy level are simultaneously finely tuned through the weak electron-withdrawing end group to serve as an excellent third component in ternary organic solar cells (TOSCs). The emission spectra of BTIC-EH-2ThBr and BTIC-BO-2ThBr mostly overlap with the absorption spectrum of the Y6 film, and efficient energy transfer is achieved from BTIC-EH-2ThBr or BTIC-BO-2ThBr to Y6. A cascade in the energy alignment could also be obtained. The morphology of the PM6:Y6:BTIC-EH-2ThBr blend film has been optimized with the addition of BTIC-EH-2ThBr as a third component. The introduction of a medium band gap molecule, BTIC-EH-2ThBr, alleviates excessive aggregation behavior and the crystallinity of the PM6:Y6 blend film. In this way, a high efficiency ternary device has been obtained with improved charge separation, transportation, collection and reduced exciton recombination. Overall, a TOSC based on PM6:Y6:BTIC-EH-2ThBr delivers the highest photovoltaic performance of 17.54% with enhanced photo utilization.