Fig. 1

Schematics of scanning probe microscopies for perovskite solar cells, wherein TiO2 film is used as the electron transport layer, and 2,2’,7,7’-Tetrakis(N,N-di-p-methoxyphenylamino)−9,9’-spirobifluorene (Spiro-OMeTAD) film is used as the hole transport layer; details of such solar cell architecture can be found in a recent review12