Expanding the conjugated benzene rings of phenothiazine phosphonic acid for efficient tin–lead mixed perovskite solar cells with a Sn/Pb ratio of 0.4 : 0.6

A novel molecule 4-(13 H -dibenzo[ b , i ]phenothiazin-13-yl)butyl phosphonic acid with the expanded π-conjugation was designed to solve the critical interfacial issues of tin–lead mixed perovskite solar cells, achieving a record efficiency for the Sn 0.4 Pb 0.6 branch.