Fullerene-based carboxylic acids for improving performance and stability of perovskite solar cells

We report a family of fullerene-based carboxylic acids with varied molecular structure affecting their ability to anchor to the surface of metal oxides, in particular SnO₂, used as electron-transport materials in n-i-p perovskite solar cells. Compounds having the lowest solubility and/or increased number of carboxyl groups per fullerene core tend to form more robust passivation coatings over SnO₂ and thus deliver the highest solar cell efficiencies and the best device operational stabilities. The results indicate the promise of further rational design of the fullerene-based acids with improved properties to achieve simultaneously a high solar light conversion efficiency and a long-term stability.