Molecular engineering of tetracene-fullerene adducts: Searching for new electron acceptor materials used in polymer photovoltaic cells

It is well known that the electronic properties of organic semiconductors are largely determined by their solid state structures. In conjugated polymer-based photovoltaic devices, fullerene derivatives such as [6,6]-phenyl-C₆₁-butyric acid methyl esters (PCBM) are used prevalently as the electron acceptor materials because of their excellent processability, electron affinity and compatibility with donor conjugated polymers. However, the crystal packing of these materials is merely controllable even if the micro- or nanocrystals formed in polymer/PCBM blends are found to be critical to the overall performance. Our work herein is to develop new fullerene-based n-type materials through [4+2] Diels-Alder reaction between substituted tetracenes and C₆₀. The molecular structures, solid state structures and photovoltaic properties measured from a standard poly(3-hexylthiophene) (P3HT)/acceptor photovoltaic device of these new adducts are carefully correlated. The ultimate goal is searching for materials outperforming PCBM that can also provide room for solid state structure manipulation.