Controlled growth of PbI₂ nanoplates for rapid preparation of CH₃NH₃PbI₃ in planar perovskite solar cells

Abstract

Absorbers for planar perovskite solar cells are often prepared by two‐step deposition methods, where a thick compact PbI 2 layer is deposited followed by conversion to perovskite using CH 3 NH 3 I solution. The surface of the precursor layer quickly reacts with the CH 3 NH 3 I solution, which hinders further diffusion of CH 3 NH 3 I into the layer, consequently leading to significant amounts of residual PbI 2 at room temperature. Here, we report a novel concept that employs a porous nanostructured PbI 2 layer consisting of nanoplates to rapidly prepare single phase perovskite layer. The non‐compact nanoplate morphology is achieved in a controllable manner by thermal evaporation of PbI 2 on TiO 2 ‐coated FTO substrate and allows easy penetration of CH 3 NH 3 I solution into the whole PbI 2 layer, thus facilitating fast and complete conversion. The amount of PbI 2 residual can be controlled by varying the CH 3 NH 3 I concentration. The growth of the nanoplates is governed by the intrinsic crystallographic structure of the deposited material, crystal characteristics of the underlying substrate, and deposition method. The introduced process enables planar perovskite solar cells with efficiency of 8.6% measured at maximum power point. This work opens a new route for rapid preparation of other three‐dimensional organic–inorganic hybrid perovskites by rational tailoring the metal halide morphology.