Achieving γ‐Phase CsPbI3 by Reducing Underlayer Surface Roughness.

Cesium lead iodide (CsPbI3) exhibits great potential in developing photovoltaic cells due to suitable optical bandgap and thermal stability. However, the photoactive γ‐phase normally exists at high‐temperatures ≈180 °C, and it is challenging to obtain γ‐phase CsPbI3 at room temperature. Here, it discovers that γ‐phase CsPbI3 is achievable by reducing the underlayer surface roughness to a certain level. This method is universal as demonstrated on the surface of poly(3,4‐ethylenedioxythiophene) poly(styrene sulfonate) (PEDOT:PSS), poly[bis(4‐phenyl)(2,4,6‐trimethylphenyl)amine] (PTAA), polystyrene (PS), and silicon substrates. Moreover, it is found that lower surface roughness resulted in smaller crystallite size in the CsPbI3 film, which is an important reason for achieving γ‐phase because the decrease in crystallite size will increase grain surface energy to suppress tilting of PbI6 octahedra and lattice distortion. This study offers a universal approach to obtain γ‐phase CsPbI3 for the development of high‐performance all‐inorganic perovskite solar cells and other optoelectronic devices. [ABSTRACT FROM AUTHOR]