Nano-scale smooth surface of the compact-TiO2 layer via spray pyrolysis for controlling the grain size of the perovskite layer in perovskite solar cells

Abstract

The mechanism of perovskite film growth is critical for the final morphology and, thus, the performance of the perovskite solar cell. The nano-roughness of compact TiO₂ (c-TiO₂) fabricated via the spray pyrolysis method had a significant effect on the perovskite grain size and perovskite solar cell performance in this work. While spray pyrolysis is a low-cost and straightforward deposition technique suitable for large-scale application, it is influenced by a number of parameters, including (i) alcoholic solvent precursor, (ii) spray temperature, and (iii) annealing temperature. Among alcoholic solvents, 2-propanol and 1-butanol showed a smooth surface without any large TiO₂ particles on the surface compared to EtOH. The lowest roughness of the c-TiO₂ layer was obtained at 450 °C with an average perovskite grain size of around 300 nm. Increased annealing temperature has a positive effect on the roughness of TiO₂. The highest efficiency of the solar cell was achieved by using 1-butanol as the solvent. The decrease in the nano roughness of c-TiO₂ promoted larger perovskite grain sizes via a relative decrease in the nucleation rate. Therefore, controlling the spray pyrolysis technique used to deposit the c-TiO₂ layer is a promising route to control the surface nanoroughness of c-TiO₂, which results in an increase in the MAPbI₃ grain size.