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It is important to highlight that in certain specialized industries, humidity detection limit is increasingly stringent. The dynamic range of humidity measurement can be expanded from low relative humidity levels to measurements at the ppm, ppb, or even ppt level. The increasingly tight humidity detection limits, especially in some industries, make this growth all the more important. Two major obstacles prevent the development of high-performance low-humidity sensors based on nanostructured materials: first, the sensor's small water-molecule-absorbing capacity, and second, the restrictions imposed by some harsh environments. As of right now, there are few comprehensive reviews of studies done on trace and low humidity sensors. With any luck, the findings of this research will shed light on how low/trace humidity sensors should be developed, which should speed up the production of high-performance materials and encourage the use of better methods for controlling low humidity. Initially, our attention has been directed toward evaluating the contemporary market outlook and the significance of trace/low humidity sensors, encapsulating the evolutionary trends observed in recent years. We have explored the advancements made and the critical issues requiring attention over the past decade. In conclusion, we have provided a summary and offered insights into the future direction of low and trace humidity sensors. [ABSTRACT FROM AUTHOR]

Success in photovoltaic power generation has raised a huge possibility in metal halide perovskites to exhibit excellent photodetection performance with the same physics of photocarrier generation, and their collection at terminal electrodes is employable with less defect-assisted carrier recombination loss. To test this, nanostructured Ruddlesden–Popper (RP)-layered perovskite series were synthesized based on a cyclic organic moiety and Br– halide, resulting in (CH)2(MA)n−1PbnBr3n+1 [where CH2-(1-cyclohexenyl) ethylamine, MAmethylammonium, Brbromine, and n = 1–4], to explore how best its mono-to-few layer (n) 2D and quasi 2D-structures can offer photodetection performance with maximum absorbance in the unexplored blue-to-green band gap RP perovskites with maximum stability. Thermogravimetric analysis revealed that the very stable nature of these RP perovskites is accompanied by a linear rise in the structural phase transition temperatures, which range from 270 °C (CH)2PbBr4 (n = 1) to 304 °C (CH)2(MA)3Pb4Br13. The RP perovskites (CH)2(MA)n−1PbnBr3n+1 (n = 1–4) demonstrated sharp exciton emission peaks from blue (∼408 nm) to green (∼528 nm). The X-ray diffraction results confirmed the highly crystalline nature of quasi-2D perovskite thin films. Layer-dependent photoluminescence studies exhibit strong room-temperature exciton photoluminescence and high carrier lifetime. The transient photocurrent measurements for (CH)2(MA)3Pb4Br13 (n = 4) RP perovskite thin films show nearly six times the bias voltage changed from 1 to 5 V at 405 nm laser light excitation. In addition, with respect to performance, the (CH)2(MA)3Pb4Br13 photodetector has shown the highest responsivity (67.2 mA/W), ultrafast transient photocurrent response (122 nA), and high EQE (20.6%) as compared to (CH)2(MA)2Pb3Br10 (n = 3) and (CH)2(MA)-Pb2Br7 (n = 2) in ambient temperature. [ABSTRACT FROM AUTHOR]

We document the fabrication and investigations of a novel photodetector based on a WS 2 quantum dots and reduced graphene oxide (RGO) (WS 2 -QDs/RGO) heterostructure. The proposed photodetector is simple, scalable, cost-effective, and flexible and works in an ambient environment. An enhanced photodetection efficiency is observed due to the superior electronic properties of WS 2 -QDs and excellent electrical as well as thermal properties of the carrier transportation medium, RGO. For device fabrication, GO and WS 2 -QDs were separately synthesized via different chemistry followed by decorating WS 2 -QDs on RGO coated cotton textile. Characterization studies confirm the transformation of exfoliated WS 2 -2D flakes into WS 2 -0D quantum dots and graphene oxide (GO) to RGO. The optimized photodetection performance of WS 2 -QDs/RGO demonstrates its photoresponsivity of 5.22 mA W -1 at 1.4 mW mm -2 power density of a 405 nm illumination source. Other sensor parameters such as photosensitivity (∼20.2%), resolution (∼0.031 mW mm -2 μA -1 ), response time (1.57 s), recovery time (1.83 s), and specific detectivity (∼1.6 × 10 6 jones) are found for WS 2 -QDs/RGO sensor, and a few of these parameters are comparable and even superior to some of the devices as reported. Photosensing mechanism is explained in terms of charge transfer caused by appropriate band alignment across the interface between WS 2 -QDs and RGO, where dimensionality and quantum confinement of nanostructures synergistically enhance the overall performance of the heterostructure. The device flexibility is examined through bending, stretching, and twisting experiments and successfully demonstrated its potentiality. Sensor performance even after being soaked in water and subsequent drying shows the possibility of reuse. The attributes of flexibility, high sensitivity and responsivity, superior resolution, and cost-effectiveness of our novel flexible photodetector indicate its promising potential for flexible and wearable optical detectors operating in UV band. Although negative photoconductance of the WS 2 -QDs/RGO sensor is a major cause for not allowing the sensor to show its best performance, a trade-off is made with improved device design to qualify the expectations of being a competitive device, and this has been demonstrated with experimental facts.