CHNHPbI grain growth and interfacial properties in meso-structured perovskite solar cells fabricated by two-step deposition.

Although the two-step deposition (TSD) method is widely adopted for the high performance perovskite solar cells (PSCs), the CHNHPbI perovskite crystal growth mechanism during the TSD process and the photo-generated charge recombination dynamics in the mesoporous-TiO (mp-TiO)/CHNHPbI/hole transporting material (HTM) system remains unexploited. Herein, we modified the concentration of PbI () solution to control the perovskite crystal properties, and observed an abnormal CHNHPbI grain growth phenomenon atop mesoporous TiO film. To illustrate this abnormal grain growth mechanism, we propose that a grain ripening process is taking place during the transformation from PbI to CHNHPbI, and discuss the PbI nuclei morphology, perovskite grain growing stage, as well as Pb:I atomic ratio difference among CHNHPbI grains with different morphology. These -dependent perovskite morphologies resulted in varied charge carrier transfer properties throughout the mp-TiO/CHNHPbI/HTM hybrid, as illustrated by photoluminescence measurement. Furthermore, the effect of CHNHPbI morphology on light absorption and interfacial properties is investigated and correlated with the photovoltaic performance of PSCs.