The controllability of PbI2 morphology via nanorod-shaped underlying layer for solution-based perovskite two-step sequential deposition

Perovskite solar cells have attracted much attention recently because of their high conversion efficiency enabling to fabricate at low-cost solution-based process. However, the high-quality perovskite via two-step sequential deposition hinges on the morphological structure of lead iodide (PbI2) that directly affects its conversion into the perovskite. Herein, we demonstrate a facile approach to optimize the quality of two-step sequential perovskite by manipulating the morphology of PbI2 via the utilization of hydrothermally synthesized TiO2 nanorod arrays as the underlying layer. Our result reveals that the nanorod-shaped TiO2 arrays composed of internanorod spaces can offer an improved wettability to the solution-based PbI2 coating. The variation of inter-nanorod spaces with TiO2 nanorod lengths plays a crucial role in attaining the morphology of PbI2 film with tunable porous structure, facilitating the interfacial reaction with methylammonium iodide. The perovskite solar cell formed on the proper TiO2 nanorod arrays can deliver a better device performance than that of the improper counterparts, leading to the increase of the conversion efficiency from 11.98% to 13.05%. Such a boosted result from the optimized underlying layer can be ascribed for the improvement of the surface roughness and the converted process of PbI2, beneficial for achieving a high-quality perovskite film.