Vortex Flow Induced Self-Assembly in CsPbI3 Rods Leads to Improved Electrical Response Towards External Analyte

We present a facile and versatile strategy for enabling CsPbI3 rods to self-assemble at an air-water interface. The CsPbI3 rods, which float at the air-water interface, align under the influence of the rotational flow field due to the vortex motion of a water subphase. The aligned CsPbI3 rods could be transferred onto various substrates without involving any sophisticated instrumentation. The temperature of the subphase, the concentration of the CsPbI3 aliquot, the rotational speed inducing vortex motion, and the lift-off position and angle of the substrate were optimized to achieve high coverage of the self-assembled rods of CsPbI3 on glass. The Rietveld refinement of the XRD profile confirms that the aligned CsPbI3 is in the pure orthorhombic phase ascribed to the Pnma space group. The hydrophilic carboxylic group of the oleic acid attaches to the Pb atoms of the halide perovskite rods, while their hydrophobic tails encapsulate the rods within their shell, creating a shielding barrier between the water and the perovskite surface like a reverse micelle. The aligned CsPbI3 rods exhibit a nearly 47-fold increment in current upon exposure to ammonia gas (amounting to 5.6 times higher sensitivity in ammonia sensing) compared to the non-aligned CsPbI3 rods.