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

Absorbers for planar perovskite solar cells are often prepared by two-step deposition methods, where a thick compact PbI2 layer is deposited followed by conversion to perovskite using CH3NH3I solution. The surface of the precursor layer quickly reacts with the CH3NH3I solution, which hinders further diffusion of CH3NH3I into the layer, consequently leading to significant amounts of residual PbI2 at room temperature. Here, we report a novel concept that employs a porous nanostructured PbI2 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 PbI2 on TiO2-coated FTO substrate and allows easy penetration of CH3NH3I solution into the whole PbI2 layer, thus facilitating fast and complete conversion. The amount of PbI2 residual can be controlled by varying the CH3NH3I 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.