Self-Powered Humidity Sensor Driven by Triboelectric Nanogenerator Composed of Bio-Wasted Peanut Skin Powder.

The increasing number of IoT devices has led to more electronic waste production, which harms the environment and human health. Self-powered sensor systems are a solution, but they often use toxic materials. We propose using biocompatible peanut skin as the active material for a self-powered humidity sensor (PSP-SPHS) through integration with a peanut-skin-based triboelectric nanogenerator (PSP-TENG). The PSP-TENG was characterized electrically and showed promising results, including an open circuit voltage (162 V), short circuit current (0.2 µA), and instantaneous power (2.2 mW) at a loading resistance of 20 MΩ. Peanut skin is a great choice for the sensor due to its porous surface, large surface area, eco-friendliness, and affordability. PSP-TENG was further used as a power source for the PSP-humidity sensor. PSP-SPHS worked as a humidity-dependent resistor, whose resistance decreased with increasing relative humidity (%RH), which further resulted in decreasing voltage across the humidity sensor. This proposed PSP-SPHS exhibited a good sensitivity (0.8 V/RH%), fast response/recovery time (4/10 s), along with excellent stability and repeatability, making it a potential candidate for self-powered humidity sensor technology.

Highly Sensitive and Stable Humidity Sensor Based on the Bi-Layered PVA/Graphene Flower Composite Film.

Two-dimensional (2D) materials and their composites have gained significant importance as the functional layer of various environmental sensors and nanoelectronics owing to their unique properties. This work reports for the first time a highly sensitive, fast, and stable humidity sensor based on the bi-layered active sensing area composed of graphene flower (GF) and poly (vinyl alcohol) PVA thin films for multifunctional applications. The GF/PVA humidity sensor exhibited stable impedance response over 15 days, for a relative humidity (RH) range of (40-90% RH) under ambient operating conditions. The proposed bi-layered humidity sensor also exhibited an ultra-high capacitive sensitivity response of the 29 nF/%RH at 10 kHz and fast transient response of 2 s and 3.5 s, respectively. Furthermore, the reported sensor also showed a good response towards multi-functional applications such as non-contact skin humidity and mouth breathing detection.

A Full-Range Flexible and Printed Humidity Sensor Based on a Solution-Processed P(VDF-TrFE)/Graphene-Flower Composite.

A novel composite based on a polymer (P(VDF-TrFE)) and a two-dimensional material (graphene flower) was proposed as the active layer of an interdigitated electrode (IDEs) based humidity sensor. Silver (Ag) IDEs were screen printed on a flexible polyethylene terephthalate (PET) substrate followed by spin coating the active layer of P(VDF-TrFE)/graphene flower on its surface. It was observed that this sensor responds to a wide relative humidity range (RH%) of 8-98% with a fast response and recovery time of 0.8 s and 2.5 s for the capacitance, respectively. The fabricated sensor displayed an inversely proportional response between capacitance and RH%, while a directly proportional relationship was observed between its impedance and RH%. P(VDF-TrFE)/graphene flower-based flexible humidity sensor exhibited high sensitivity with an average change of capacitance as 0.0558 pF/RH%. Stability of obtained results was monitored for two weeks without any considerable change in the original values, signifying its high reliability. Various chemical, morphological, and electrical characterizations were performed to comprehensively study the humidity-sensing behavior of this advanced composite. The fabricated sensor was successfully used for the applications of health monitoring and measuring the water content in the environment.

Polarization Reversal Characteristics in Capacitors with a Metal/Insulator/Ferroelectric/Metal Structure.

A metal/insulator/ferroelectric/metal structure was fabricated using a covering of approximately 10 nm thick of an insulating polystyrene film on a ferroelectric poly(vinylidene fluoride-trifluoroethylene) film. To fabricate several samples, the thickness of the ferroelectric film was held constant while the thickness of the insulating film was varied from 8 to 24 nm. The polarization- voltage relationships were measured to extract the main parameters, in this case the remanent polarization, depolarization, coercive voltage and biased voltage values. As the insulating film becomes thicker, the remanent polarization and coercive voltage values tended to increase. On the other hand, depolarization and biased voltage values decreased. By analyzing the above mentioned parameters, a certain optimum insulator thickness could be predicted. This work shows that metal/insulator/ferroelectric/metal devices are more useful than metal/ferroelectric/metal capacitors.

Polarization Reversal Characteristics of Ferroelectric-Schottky Diode Hybrid Structure.

The polarization reversal characteristics were measured by fabricating a device with top electrode/n-type semiconductor/ferroelectric/bottom electrode structure. It was observed that the hysteresis curves were changed according to the polarity of the applied voltage. When a positive voltage was applied, depolarization was hardly observed. However, a significant depolarization occurred when a negative voltage was applied. An attempt was made to set up an equivalent circuit using a Schottky diode to model the semiconductor-ferroelectric structure. This study is expected to be useful for setting protocol of electronic device composed of semiconductor-ferroelectric hybrid structure.

Effect of Randomly Grown Morphology of ZnO Nanorods in Inverted Organic Solar Cells.

Here, we analyzed the photovoltaic properties of the inverted organic solar cells (IOSCs) by using randomly oriented medium density ZnO nanorods (ZnO-NR) synthesized hydrothermally at low temperature conditions to avoid morphological defects. The IOSC with ZnO-NR (length < 150 nm) of medium density and random orientation showed an improvement of 83% in power conversion efficiency compared to the cell with (length < 20 nm) hydrothermally grown ZnO-NR. The optimized hydrothermal growth conditions for ZnO-NR enhanced the photovoltaic performance indicators by reducing recombination rate evidenced by the photovoltaic data. The qualitative elemental analysis of the ZnO-NR based interface was performed by the EDX, which confirmed that the as-grown ZnO-NR contain the Zn and O elements.

Characterization of a Ferroelectric-Gated Graphene Memory Device Fabricated on a Flexible Substrate by Transfer Process.

The mechanical flexibility of both ferroelectric polymer and graphene provides the possibility for the memory device based on ferroelectric polymer and grapheme to operate on flexible substrate. Here, a memory device was fabricated on flexible substrate through the continuous transfer process of the two units with the ferroelectric polymer and the graphene hybrid film as one unit, and characterized. In particular, characteristics were maintained even with repetitive bending. The transfer process demonstrated in this paper is useful for implementing a memory device on a large-area substrate by consuming a very small amount of graphene.