Vortex flow induced self-assembly in CsPbI3 rods leads to an improved electrical response towards external analytes.

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.

High sensitivity NH3 gas sensor with electrical readout made on paper with perovskite halide as sensor material.

In this paper we report a cheap, paper electronics based solid state gas sensor to detect NH3 gas selectively with a detection capability of better than 1 ppm. The sensor uses perovskite halide CH3NH3PbI3 (MAPI) as the active sensor material grown on a paper. This paper based sensor works at room temperature. The current through the paper sensor increases by one order on exposure to only 10 ppm NH3 gas. The calibrated sensitivity is ~55% for 1 ppm of NH3 gas in Nitrogen or Air. The current noise limited resolution estimated to be ~10 ppb. This work establishes perovskite halide as a new solid state gas sensing material that can reach sub ppm sensitivity using simple paper electronics. Use of paper and also solution method used to grow the active material makes the sensor cost effective and easy to manufacture. This type of disposable high sensitive paper sensor can be used for detection of NH3 as a marker in exhaled breathes for non-invasive diagnosis. The sensor formed on the paper, since it supports unheated operation, needs less than few nanowatt power for its operation.

Fast response paper based visual color change gas sensor for efficient ammonia detection at room temperature.

We show that a cheap, disposable type rapid paper sensor (working at room temperature) can be made using perovskite halide CH3NH3PbI3 (MAPI) to detect presence of the toxic ammonia gas (NH3)by just color change, where the black colored MAPI film (on the paper) changes to yellow color in presence of a very low concentration of NH3 gas. The sensor can detect presence of NH3 gas in open or closed atmosphere down to around 10 ppm with a response time of nearly 10 sec which decreases to few seconds when the concentration exceeds 20 ppm. The easy to fabricate sensor paper being a visual sensor does not need any other extra equipment for its operation. The sensor is not sensitive to moisture with RH upto 90% and does not also respond to gases like Methane (CH4), Nitrous Oxide (N2O), Carbon dioxide (CO2) etc in the test chamber each up to a concentration of 500 ppm. Conversion/decomposition of MAPI to PbI2 on exposure to NH3 has been proposed as the mechanism of color change and the mechanism has been established using a collection of techniques like XRD, EDX, UV-Visible absorption and Photo Luminescence.