CH₃NH₃PbI₃ grain growth and interfacial properties in meso-structured perovskite solar cells fabricated by two-step...

Although the two-step deposition (TSD) method is widely adopted for the high performance perovskite solar cells (PSCs), the CH₃NH₃PbI₃ perovskite crystal growth mechanism during the TSD process and the photo-generated charge recombination dynamics in the mesoporous-TiO₂ (mp-TiO₂)/CH₃NH₃PbI₃/hole transporting material (HTM) system remains unexploited. Herein, we modified the concentration of PbI₂ (C_(PbI2)) solution to control the perovskite crystal properties, and observed an abnormal CH₃NH₃PbI₃ grain growth phenomenon atop mesoporous TiO₂ film. To illustrate this abnormal grain growth mechanism, we propose that a grain ripening process is taking place during the transformation from PbI₂ to CH₃NH₃PbI₃, and discuss the PbI₂ nuclei morphology, perovskite grain growing stage, as well as Pb:I atomic ratio difference among CH₃NH₃PbI₃ grains with different morphology. These C_(PbI2)-dependent perovskite morphologies resulted in varied charge carrier transfer properties throughout the mp-TiO₂/CH₃NH₃PbI₃/HTM hybrid, as illustrated by photoluminescence measurement. Furthermore, the effect of CH₃NH₃PbI₃ morphology on light absorption and interfacial properties is investigated and correlated with the photovoltaic performance of PSCs.