Facile Dimension Transformation Strategy for Fabrication of Efficient and Stable CsPbI 3 Perovskite Solar Cells.

All-inorganic cesium lead triiodide (CsPbI 3 ) perovskite has received increasing attention due to its intrinsic thermal stability and suitable band gap for photovoltaic applications. However, it is difficult to deposit high-quality pure-phase CsPbI 3 films using CsI and PbI 2 as precursors due to the rapid nucleation and crystal growth by the solution coating method. Here, a simple cation-exchange approach is employed to fabricate all-inorganic 3D CsPbI 3 perovskite, where 1D ethylammonium lead (EAPbI 3 ) perovskite is first solution-deposited and then transformed to 3D CsPbI 3 via ion exchange between EA + and Cs + during thermal annealing. The large space between the PbI 3 - skeletons in 1D EAPbI 3 favors the cation interdiffusion and exchange for the formation of pure-phase 3D CsPbI 3 with full compactness and high crystallinity and orientation. The resulting CsPbI 3 film exhibits a low trap density of state and high charge mobility, and the perovskite solar cell shows a power-conversion efficiency of 18.2% with enhanced stability. This strategy provides an alternative and promising fabrication route for the fabrication of high-quality all-inorganic perovskite devices.