From Binary to Ternary: Improving the External Quantum Efficiency of Small-Molecule Acceptor-Based Polymer Solar Cells with a Minute Amount of Fullerene Sensitization

Ternary blend is proved to be a potential contender for achieving high efficiency in organic photovoltaics, which can apparently strengthen the absorption of active layer so as to better harvest light irradiation. Much of the previous work in ternary polymer solar cells focuses on broadening the absorption spectrum; however, a new insight is brought to study the third component, which in tiny amounts influents the small-molecule acceptor-based device performance. Without contributing to complementing the absorption, a minute amount of fullerene derivative, Bis-PC70BM, can effectively play an impressive role as sensitizer in enhancing the external quantum efficiency of the host binary blend, especially for polymeric donor. Detailed investigations reveal that the minute addition of Bis-PC70BM can realize morphology modification as well as facilitate electron transfer from polymeric donor to small molecule acceptor via cascade energy level modulation, and therefore lead to an improvement in device efficiency.