Nanostructures in Dye-Sensitized and Perovskite Solar Cells

Due to increase of attention in energy and environmental concerns, there has been much interest developed in clean and renewable energy technologies. The utilization of green and eco-friendly sunlight through solar cells like photovoltaic cells, photo-electrochemical cells, and dye-sensitize and perovskite solar cells (DSSCs and PSCs) produces energy demand. Due to high electron mobility, suitable band alignment, and high optical transparency, the binary and ternary transition metal oxide materials such as TiO2, SnO2, ZnO, WO3, Bi2O3 and SrTiO3, Zn2SnO4, BaSnO3, etc. have attracted considerable attention as DSSC and PSC electrode materials. Highly efficient solar cells with sustainable performance under severe mechanical deformations are in great demand in forming wearable power supply devices, essential for space technologies. In this regard, myriads of studies have progressed in developing the said metal oxides by various means of nanostructure forms. The aim of this chapter is to highlight research background, basic concepts, operating parameters, working principles, theoretical aspects, and selection of materials with essential properties for DSSCs and PSCs applications

Hybrid composite polyaniline-nickel hydroxide electrode materials for supercapacitor applications

Pristine and nanocomposite (NC) hybrid electrodes of polyaniline (PANI)-nickel hydroxide [Ni(OH)2] have been prepared by single and two-step electrodeposition processes, respectively, onto stainless-steel (SS) substrates. Enhanced reversibility and stability of amorphous PANI- Ni(OH)2 NC electrodes compared to single electrode materials have been explored. PANI has a nanofibrous morphology, Ni(OH)2 has nanoplatelet-type morphology, and the NC electrodes retain an overall nanofibrous morphology. The maximum specific capacitance (SC), obtained from integrated charge under voltammetric conditions, for PANI (electro-deposited for 5 min), NC (electrodeposition of Ni(OH)2 for 10 min and 20 min onto PANI electrode surface) and Ni(OH)2 (electrodeposited for 10 min) electrodes, are 0.59, 39.06, 32.36, and 113.8 F/g, respectively, suggesting higher electrochemical performance of Ni(OH)2 electrode compared to PANI and NC electrodes. The retention in SC values with faster scan rates from 10 to 100 mV/s for PANI, NC (10 min), NC (20 min) and Ni(OH)2 are 38.7, 61.1, 52.4, and 29.0 %, respectively, explicitly confirming a higher reversibility in NC electrodes. The retention in SC values with increase of cycle number up to 1000 for PANI, NC (10 min), NC (20 min) and Ni(OH)2 electrodes are 34.9, 61.5, 67.5, and 40.7 % respectively, demonstrating higher electrochemical stability of NC electrodes over pure-phase electrodes. Nearly 2.15, 79.36, 66.66 and 406.83 mC/cm2 charges on PANI, NC (10 min), NC (20 min) and Ni(OH)2 electrodes, respectively, are obtained. Inner to total charge and outer to total charge ratios have been used to explain contributing sites to total charge in pristine and NC electrodes

Low-concentration detection of H2S using temperature-dependent Cr-doped cobalt-oxide gas sensors

Among the existing metal-oxide gas sensors, cobalt oxide has the flexibility to revise the morphology through Cr-dopant to enhance sensing properties. Sensitive-surface of the chromium-doped cobalt oxide has proven its effective sensing nature to hydrogen sulfide gas. Interestingly, chromium-dopant increases the surface area, leading to particle size reduce and produces the more active sites for gas molecules. Also, the dopant creates impurity phases on the material which extends the sites for more reaction. To confirms these characteristics, the photoluminescence spectra showed intense peak that mimics the faster transport of electron to accelerate the sensing reaction. According to sensing measurement, the doped sensor is showing three-fold increase of response to 10 ppm gas and also, it detects the 2 ppm efficiently. The doped sensor warrants the stable response to gas due to higher reproducibility. Notably, the doped sensor detects the 1 ppm of gas at 120 s and recovery itself around 200 s. The doped sensor imparts response at room-temperature, affirming sensitive-surface. The doped sensor has shown the capable under humidity environment through response

Low-temperature ionic layer adsorption and reaction grown anatase TiO 2 nanocrystalline films for efficient perovskite solar cell and gas sensor applications

A low-temperature (90 °C) and directly grown anatase titanium dioxide (TiO2) nanocrystalline film using successive ionic layer adsorption and reaction (SILAR) for perovskite solar cell and gas sensor applications. TiO2 nanocrystalline electron transfer layer (ETL) improves the power conversion efficiency (PCE) of perovskite solar cells due to faster charge transport kinetics as well as slower charge recombination process. The optimized TiO2 nanocrystalline ETL (15 L) demonstrates as high as ~10% PCE with a short circuit current density of 18.0 mA/cm2, open circuit voltage of 0.81 V and fill factor of 66.3% in perovskite solar cells. Furthermore, room-temperature ammonia sensing characteristics of TiO2 nanocrystalline film (25 L) were  demonstrated for various concentration levels of ammonia in dry air conditions. A high room-temperature response of 80% was achieved at 100 ppm of ammonia with rapid response and recovery signatures of 30 and 85 s, and nearly fifteen days stability, respectively. The response of the sensor to other gases such as formaldehyde, petrol, ethanol acetone, and ammonia etc, indicated a high selectivity towards volatile organic compounds of ammonia gas. The room temperature operation, with high selectivity, repeatability and fast transition times, suggests potentially useful in flexible and cost-effective production in optoelectrochemical device technology

Gold sensitized sprayed SnO2 nanostructured film for enhanced LPG sensing

We report LPG sensing of gold (Au)-sensitized SnO2 nanostructured film fabricated by an easy spray pyrolysis deposition method whose surface morphology is confirmed by field-emission scanning electron microscopy and atomic force microscopy images and structure by X-ray diffraction pattern. Energy dispersive X-ray spectrometer analysis has carried out for finding elemental composition. The SnO2 film is uniform and consists of spherical particles of ∼10nm. The highest gas response observed at 780ppm LPG concentration for pristine SnO2 is 28%, at operating temperature 623K, which is greatly improved on Au sensitization up to 57% with 60s rapid response time at 598K operating temperature. The high gas response is due to electronic effect and catalytic spill-over effect of Au sensitization. The improved sensing mechanism has throughly been explored

Metal-free heterogeneous and mesoporous biogenic graphene-oxide nanoparticle-catalyzed synthesis of bioactive benzylpyrazolyl coumarin derivatives

We report the preparation of graphene oxide nanoparticles (GONPs), a metal-free, heterogeneous, non-toxic, reusable and mesoporous green-(acid)-catalyst obtained by sugar carbonization through a micro-wave chemical synthesis method for the synthesis of bio-active benzylpyrazolyl coumarin derivatives (BCDs) under thermal conditions (50 [degree]C) in ethanol solvent. The obtained products were purified by re-crystallization from ethanol, assuring usability of GONPs in multicomponent reactions (MCRs) that could find wide application in the synthesis of a variety of biologically potent molecules of therapeutic significance

Resistive Ammonia Gas Sensor Based on Non-Stoichiometric Copper Sulfide Thin Films

Resistive ammonia gas sensor is fabricated by using solution growth technique deposited copper sulfide (Cu1.8S) thin films. Structural and opto-electronic properties of the films are studied by X-ray diffraction, atomic force microscopy, optical absorbance and electrical resistance. Ammonia gas sensor response measured from 20 to 500 ppm concentration at room temperature (300 K). The sensor response is increases with gas concentration

Photosensitization of ZnO nanowire-based electrodes using one-step hydrothermally synthesized CdSe/CdS (core/shell) sensitizer

One-step assembled CdSe/CdS (core/shell) quantum dots (QDs) were deposited onto ZnO nanowires (NWs) and characterized for their structure, morphology and optical analyses. As deposited ZnO NWs array were wurtzite in structure. During a single hydrothermal cycle a layer of ~4nm CdSe/CdS QDs was formed onto ZnO NWs and overgrowth evidenced with an additional 2-5 layers due to which, (a) absorbance density, and (b) Raman Shift of 1LO mode (from 286cm-1 to 296cm-1) increased and (c) the photoluminescence intensity of the near band-edge emission peak at ~379nm decreased. Due to more accumulation of CdSe/CdS, photoelectrochemical cells of ZnO-based photoelectrodes designed for 1-4 cycles of CdSe/CdS onto indium-tin-oxide substrate demonstrated increasing power conversion efficiency trend from 0.18% to 1.29% whereas, for 5th cycle power conversion efficiency, due to an increased series resistance, decreased to 1.12% on account of an accumulation of several QDs