Well-Separated Photoinduced Charge Carriers on Hydrogen Production Using NiS2/TiO2 Nanocomposites

Photocatalytic hydrogen production is a sustainable and greenhouse-gas-free method that requires an efficient and abundant photocatalyst, which minimizes energy consumption. Currently, interests in transition metal chalcogenide materials have been utilized in different applications due to their quantum confinement effect and low band gaps. In this study, different wt % of NiS2-embedded TiO2 nanocomposites were synthesized by a facile hydrothermal method and utilized for photocatalytic hydrogen production under extended solar irradiation. Among the materials studied, the highest amount (4.185 mmol g-1) of hydrogen production was observed with 15 wt % of the NiS2/TiO2 nanocomposite. The highest photocatalytic activity may be due to the well separation of photoinduced charge carriers on the catalyst, which was confirmed by the electrochemical studies. Thus, we believe that these photocatalysts are promising candidates for future applications.

Hybrid Functional Study on Electronic and Optical Properties of the Dopants in Anatase TiO2

TiO2 was known as a golden heterogeneous photocatalyst due to its chemical stability, low cost, nontoxicity, and strong oxidizing power. However, anatase TiO2 predominantly absorbs the photon energy in the ultraviolet region (λ < 387.5 nm); therefore, to increase the utilization of sunlight, the approach of doping of metals and nonmetals into pure TiO2 is implemented. Here we incorporate the dopants of Zr, Si, V, W, Ge, Cr, Sn, Mo, and Pb into the TiO2 lattice and study the optoelectronic properties, including the formation energies and the electron charge distributions, using the Vienna ab initio Simulation Package (VASP) from the hybrid functional of Heyd, Scuseria, and Erhzerhof (HSE06). We observed that V-, Mo-, and Cr-doped systems introduce shallow impurity states within the band gap, and those states influence the shift of the absorbance spectra to visible light by enhancing the photocatalytic efficiency. W-doped anatase TiO2 structure reduces the band gap of the pure anatase TiO2 by 0.7 eV. Notably, this reduction occurs without the introduction of any impurity states between the band edges. Additionally, the absorption edge of the solar spectrum shifts toward lower photon energy from 3.5 to 3.1 eV. From Bader charge analysis, we observed that mainly the charge transfer occurred from the dopants and charge accumulation happened around nearby oxygen atoms. The ferromagnetism was observed in V-, Cr-, Mo-, and W-doped anatase TiO2 structures due to the charge imbalance of the spin-up and spin-down states.

Natural sensitizer extracted from Mussaenda erythrophylla for dye-sensitized solar cell

In this study, a natural dye from the flowers of Mussaenda erythrophylla extracted separately in ethanol and de-ionized water was employed as a photosensitizer in DSSCs. The quantitative phytochemical analyses were performed on both extracts. The existence of flavonoids (anthocyanin) and chlorophyll a pigments in the ethanol extract of the dye was confirmed by the UV-Visible spectroscopy. The stability study performed on the said ethanol extract confirmed that the dye extracted in ethanol was stable in the dark and did not degrade for nearly 50 days. The presence of the dye molecules and uniform adsorption of them on the P25-TiO2 surface were confirmed by fourier transform infrared spectroscopy and atomic force microscopy, respectively. Moreover, the influence of dye concentration and pH on the optical properties of the dye was also studied. The natural dye extracted in ethanol was employed in DSSCs, fabricated by utilizing the said dye sensitized P25-TiO2 photoanodes, [Formula: see text]/[Formula: see text] electrolyte, and Pt counter electrode. Photovoltaic performances of the fabricated devices were determined under simulated irradiation with the intensity of 100 mWcm-2 using AM 1.5 filter. The device fabricated with the P25-TiO2 photoanode sensitized by the dye extracted in ethanol at pH = 5 exhibited the best power conversion efficiency (PCE) of 0.41% with the JSC of 0.98 mAcm-2 which could be attributed to the optimum light absorption in the visible region of solar spectrum by the chlorophyll a and anthocyanin molecules in the extracted natural dye.

Resistance to the larvicide temephos and altered egg and larval surfaces characterize salinity-tolerant Aedes aegypti

Aedes aegypti, the principal global vector of arboviral diseases and previously considered to oviposit and undergo preimaginal development only in fresh water, has recently been shown to be capable of developing in coastal brackish water containing up to 15 g/L salt. We investigated surface changes in eggs and larval cuticles by atomic force and scanning electron microscopy, and larval susceptibility to two widely-used larvicides, temephos and Bacillus thuringiensis, in brackish water-adapted Ae. aegypti. Compared to freshwater forms, salinity-tolerant Ae. aegypti had rougher and less elastic egg surfaces, eggs that hatched better in brackish water, rougher larval cuticle surfaces, and larvae more resistant to the organophosphate insecticide temephos. Larval cuticle and egg surface changes in salinity-tolerant Ae. aegypti are proposed to respectively contribute to the increased temephos resistance and egg hatchability in brackish water. The findings highlight the importance of extending Aedes vector larval source reduction efforts to brackish water habitats and monitoring the efficacy of larvicides in coastal areas worldwide.

Air processed Cs2AgBiBr6 lead-free double perovskite high-mobility thin-film field-effect transistors

This study focuses on the fabrication and characterization of Cs₂AgBiBr₆ double perovskite thin film for field-effect transistor (FET) applications. The Cs₂AgBiBr₆ thin films were fabricated using a solution process technique and the observed XRD patterns demonstrate no diffraction peaks of secondary phases, which confirm the phase-pure crystalline nature. The average grain sizes of the spin-deposited film were also calculated by analysing the statistics of grain size in the SEM image and was found to be around 412 (± 44) nm, and larger grain size was also confirmed by the XRD measurements. FETs with different channel lengths of Cs₂AgBiBr₆ thin films were fabricated, under ambient conditions, on heavily doped p-type Si substrate with a 300 nm thermally grown SiO₂ dielectric. The fabricated Cs₂AgBiBr₆ FETs showed a p-type nature with a positive threshold voltage. The on-current, threshold voltage and hole-mobility of the FETs decreased with increasing channel length. A high average hole mobility of 0.29 cm² s⁻¹ V⁻¹ was obtained for the FETs with a channel length of 30 µm, and the hole-mobility was reduced by an order of magnitude (0.012 cm² s⁻¹ V⁻¹) when the channel length was doubled. The on-current and hole-mobility of Cs₂AgBiBr₆ FETs followed a power fit, which confirmed the dominance of channel length in electrostatic gating in Cs₂AgBiBr₆ FETs. A very high-hole mobility observed in FET could be attributed to the much larger grain size of the Cs₂AgBiBr₆ film made in this work.

Potential transition and post-transition metal sulfides as efficient electrodes for energy storage applications: review

Electrochemical energy storage has attracted much attention due to the common recognition of sustainable energy development. Transition metal sulfides and post-transition metal sulfides have been intensively been focused on due to their potential as electrode materials for energy storage applications in different types of capacitors such as supercapacitors and pseudocapacitors, which have high power density and long cycle life. Herein, the physicochemical properties of transition and post-transition metal sulfides, their typical synthesis, structural characterization, and electrochemical energy storage applications are reviewed. Various perspectives on the design and fabrication of transition and post-transition metal sulfides-based electrode materials having capacitive applications are discussed. This review further discusses various strategies to develop transition and/or post-transition metal sulfide heterostructured electrode-based self-powered photocapacitors with high energy storage efficiencies.

Electrochemical energy storage has attracted much attention due to the common recognition of sustainable energy development.

Selective and electronic detection of COVID-19 (Coronavirus) using carbon nanotube field effect transistor-based biosensor: A proof-of-concept study

In this work, we propose and demonstrate a carbon nanotube (CNT) field-effect transistor (FET) based biosensor for selective detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). CNT FETs were fabricated on a flexible Kapton substrate and the sensor was fabricated by immobilizing the reverse sequence of the RNA-dependent RNA polymerase gene of SARS-CoV-2 onto the CNT channel. The biosensors were tested for the synthetic positive and control target sequences. The biosensor showed a selective sensing response to the positive target sequence with a limit of detection of 10 fM. The promising results from our study suggest that the CNT FET based biosensors can be used as a diagnostic tool for the detection of SARS-CoV-2.

Lithium doped poly(3-hexylthiophene) for efficient hole transporter and sensitizer in metal free quaterthiophene dye treated hybrid solar cells

This work focuses on the role of Lithium doped Poly(3-hexylthiophene)(P3HT) in metal-free quaterthiophene (4T) dye treated Titanium dioxide (TiO₂) based hybrid solar cells. The dye treated hybrid solar cells with Lithium doped P3HT showed efficiencies (3.95%) of nearly a factor of four times higher than the pristine P3HT based control TiO₂/4T/P3HT devices (1.04%). The enhancement of the efficiency is mainly due to highly efficient charge collection attributed to enhanced charge transport and light harvesting properties of Lithium doped P3HT polymer. The optimized solar cells with Lithium doped P3HT showed a high short circuit current density over 13 mA/cm², under simulated irradiation of intensity 100 mW/cm² with AM 1.5 filter. This significant increase in current density in TiO₂/4T/doped P3HT solar cell is also confirmed by both the broadened External Quantum Efficiency spectrum and significant photoluminescence quenching upon replacement of pristine P3HT with doped P3HT on 4T dye treated TiO₂ electrode. With Lithium doped Spiro-OMeTAD instead of Lithium doped P3HT, similar devices showed efficiencies over 3.30% under simulated irradiation of 100 mW/cm² with AM 1.5 filter.

Perovskite Solar Cells: A Porous Graphitic Carbon based Hole Transporter/Counter Electrode Material Extracted from an Invasive Plant Species Eichhornia Crassipes

Perovskite solar cells (PSCs) composed of organic polymer-based hole-transporting materials (HTMs) are considered to be an important strategy in improving the device performance, to compete with conventional solar cells. Yet the use of such expensive and unstable HTMs, together with hygroscopic perovskite structure remains a concern - an arguable aspect for the prospect of onsite photovoltaic (PV) application. Herein, we have demonstrated the sustainable fabrication of efficient and air-stable PSCs composed of an invasive plant (Eichhornia crassipes) extracted porous graphitic carbon (EC-GC) which plays a dual role as HTM/counter electrode. The changes in annealing temperature (~450 °C, ~850 °C and ~1000 °C) while extracting the EC-GC, made a significant impact on the degree of graphitization - a remarkable criterion in determining the device performance. Hence, the fabricated champion device-1c: Glass/FTO/c-TiO2/mp-TiO2/CH3NH3PbI3-xClx/EC-GC10@CH3NH3PbI3-x Clx/EC-GC10) exhibited a PCE of 8.52%. Surprisingly, the introduced EC-GC10 encapsulated perovskite interfacial layer at the perovskite/HTM interface helps in overcoming the moisture degradation of the hygroscopic perovskite layer in which the same champion device-1c evinced better air stability retaining its efficiency ~94.40% for 1000 hours. We believe that this present work on invasive plant extracted carbon playing a dual role, together as an interfacial layer may pave the way towards a reliable perovskite photovoltaic device at low-cost.

Powder Pressed Cuprous Iodide (CuI) as A Hole Transporting Material for Perovskite Solar Cells

This study focuses on employing cuprous iodide (CuI) as a hole-transporting material (HTM) in fabricating highly efficient perovskite solar cells (PSCs). The PSCs were made in air with either CuI or 2,2',7,7'-Tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene (spiro-OMeTAD) as HTMs. A simple and novel pressing method was employed for incorporating CuI powder layer between perovskite layer and Pt top-contact to fabricate devices with CuI, while spiro-OMeTAD was spin-coated between perovskite layer and thermally evaporated Au top-contact to fabricate devices with spiro-OMeTAD. Under illuminations of 100 mW/cm² with an air mass (AM) 1.5 filter in air, the average short-circuit current density (J_SC) of the CuI devices was over 24 mA/cm², which is marginally higher than that of spiro-OMeTAD devices. Higher J_SC of the CuI devices can be attributed to high hole-mobility of CuI that minimizes the electron-hole recombination. However, the average power conversion efficiency (PCE) of the CuI devices were lower than that of spiro-OMeTAD devices due to slightly lower open-circuit voltage (V_OC) and fill factor (FF). This is probably due to surface roughness of CuI powder. However, optimized devices with solvent-free powder pressed CuI as HTM show a promising efficiency of over 8.0 % under illuminations of 1 sun (100 mW/cm²) with an air mass 1.5 filter in air, which is the highest among the reported efficiency values for PSCs fabricated in an open environment with CuI as HTM.

Polymer/Fullerene Blend Solar Cells with Cadmium Sulfide Thin Film as an Alternative Hole-Blocking Layer

In this work, chemical bath-deposited cadmium sulfide (CdS) thin films were employed as an alternative hole-blocking layer for inverted poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) bulk heterojunction solar cells. CdS films were deposited by chemical bath deposition and their thicknesses were successfully controlled by tailoring the deposition time. The influence of the CdS layer thickness on the performance of P3HT:PCBM solar cells was systematically studied. The short circuit current densities and power conversion efficiencies of P3HT:PCBM solar cells strongly increased until the thickness of the CdS layer was increased to ~70 nm. This was attributed to the suppression of the interfacial charge recombination by the CdS layer, which is consistent with the lower dark current found with the increased CdS layer thickness. A further increase of the CdS layer thickness resulted in a lower short circuit current density due to strong absorption of the CdS layer as evidenced by UV-Vis optical studies. Both the fill factor and open circuit voltage of the solar cells with a CdS layer thickness less than ~50 nm were comparatively lower, and this could be attributed to the effect of pin holes in the CdS film, which reduces the series resistance and increases the charge recombination. Under AM 1.5 illumination (100 mW/cm²) conditions, the optimized PCBM:P3HT solar cells with a chemical bath deposited a CdS layer of thickness 70 nm and showed 50% power conversion efficiency enhancement, in comparison with similar solar cells with optimized dense TiO₂ of 50 nm thickness prepared by spray pyrolysis.

Hybrid polymer/zinc oxide photovoltaic devices with vertically oriented ZnO nanorods and an amphiphilic molecular interface layer

We report on the effect of nanoparticle morphology and interfacial modification on the performance of hybrid polymer/zinc oxide photovoltaic devices. We compare structures consisting of poly-3-hexylthiophene (P3HT) polymer in contact with three different types of ZnO layer: a flat ZnO backing layer alone; vertically aligned ZnO nanorods on a ZnO backing layer; and ZnO nanoparticles on a ZnO backing layer. We use scanning electron microscopy, steady state and transient absorption spectroscopies, and photovoltaic device measurements to study the morphology, charge separation, recombination behavior and device performance of the three types of structures. We find that charge recombination in the structures containing vertically aligned ZnO nanorods is remarkably slow, with a half-life of several milliseconds, over 2 orders of magnitude slower than that for randomly oriented ZnO nanoparticles. A photovoltaic device based on the nanorod structure that has been treated with an amphiphilic dye before deposition of the P3HT polymer yields a power conversion efficiency over four times greater than that for a similar device based on the nanoparticle structure. The best ZnO nanorod:P3HT device yields a short circuit current density of 2 mAcm(-2) under AM1.5 illumination (100 mW cm(-2)) and a peak external quantum efficiency over 14%, resulting in a power conversion efficiency of 0.20%.