Scaffold-guided crystallization of perovskite nanowire arrays

Solution-processable metal halide perovskites are being actively explored for optoelectronic devices, including active matrix displays, photodetectors, and solar cells. A critical challenge facing the widespread adoption of these materials is control over crystallization outcomes during film formation. Here, we introduce a method to grow metal halide perovskite crystals as vertical nanowire arrays with large surface areas for photophysical processes, such as exciton dissociation. The crystals are grown via a two-step process in which precursors are deposited into the cylindrical pores of anodized titanium oxide scaffolds in the first step and after immersing the infiltered scaffold in the second precursor solution, perovskite crystals start to nuclei. After 1 min of immersion, nanowires begin to form and longer immersion times will increase the nanowire’s dimension. The advantage of using this two-step method is that crystal nucleation is confined inside the TiO₂ pores, resulting in vertical growth of the nanowire arrays. FA/BAPbI₃ perovskite was chosen in this study. X-ray diffraction and photoluminescence analysis confirmed the formation of perovskite photoactive alfa polymorph. To analyze the optoelectronic properties of perovskite nanowire arrays, solar cell devices are fabricated with the porous TiO₂ and Spiro-MeOTAD as electron transport layers respectively.