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.