Shoyebmohamad F. Shaikh

Low temperature chemically synthesized rutile TiO2 photoanodes with high electron lifetime for organic dye-sensitized solar cells

Electron lifetime in mesoporous nanostructured rutile TiO2 photoanodes, synthesized via a simple, cost-effective, low temperature (50-55 °C) wet chemical process, annealed at 350 °C for 1 h and not employing any sprayed TiO2 compact layer, was successfully tailored with 0.2 mM TiCl4 surface treatment that resulted in light to electric power conversion efficiency up to 4.4%.

High‐Performance Platinum‐Free Dye‐Sensitized Solar Cells with Molybdenum Disulfide Films as Counter Electrodes

By using a radio-frequency sputtering method, we synthesized large-area, uniform, and transparent molybdenum disulfide film electrodes (1, 3, 5, and 7 min) on transparent and conducting fluorine-doped tin oxide (FTO), as ecofriendly, cost-effective counter electrodes (CE) for dye-sensitized solar cells (DSSCs). These CEs were used in place of the routinely used expensive platinum CEs for the catalytic reduction of a triiodide electrolyte. The structure and morphology of the MoS2 was analyzed by using Raman spectroscopy, X-ray diffraction, and X-ray photoemission spectroscopy measurements and the DSSC characteristics were investigated. An unbroken film of MoS2 was identified on the FTO crystallites from field-emission scanning electron microscopy. Cyclic voltammetry, electrochemical impedance spectroscopy, and Tafel curve measurements reveal the promise of MoS2 as a CE with a low charge-transfer resistance, high electrocatalytic activity, and fast reaction kinetics for the reduction of triiodide to iodide. Finally, an optimized transparent MoS2 CE, obtained after 5 min synthesis time, showed a high power-conversion efficiency of 6.0 %, which comparable to the performance obtained with a Pt CE (6.6 %) when used in TiO2 -based DSCCs, thus signifying the importance of sputtering time on DSSC performance.

Spraying distance and titanium chloride surface treatment effects on DSSC performance of electrosprayed SnO2 photoanodes

A facile electrospray synthesis method and potential dye sensitized solar cell (DSSC) application of SnO2 photoanodes (of ∼10 μm thickness) have been investigated. Nanocrystallites with irregular dimensions have similar crystallite sizes and appearance when the distance between fluorine–tin-oxide (FTO) substrate and metal capillary was increased from 4 to 8 cm (maximum limit). However, increase in metal capillary distance caused reduction in charge transfer resistance and a negative shift in the flat band potential. As a result, electron lifetime was increased with the open circuit voltage (410 to 510 mV). Under 1 sun light intensity, the SnO2 photoanode (obtained at 8 cm) by a thin layer of TiO2 exhibited as high as 5.56% power conversion efficiency which was ∼350% higher than only SnO2 (1.66%) photoanode. This enhanced DSSCs performance could be attributed to better dye adsorption and increased active surface area, or boosted light-harvesting efficiency. The presence of TiO2 layer on SnO2 photoanode was confirmed with X-ray diffraction and Raman shift analysis measurements. The electrochemical impedance spectroscopy revealed increased electron lifetime and suppressed charge recombination for SnO2 photoanode that was modified with TiO2 compact surface layer.

D-sorbitol-induced phase control of TiO2 nanoparticles and its application for dye-sensitized solar cells.

Using a simple hydrothermal synthesis, the crystal structure of TiO2 nanoparticles was controlled from rutile to anatase using a sugar alcohol, D-sorbitol. Adding small amounts of D-sorbitol to an aqueous TiCl4 solution resulted in changes in the crystal phase, particle size, and surface area by affecting the hydrolysis rate of TiCl4. These changes led to improvements of the solar-to-electrical power conversion efficiency (η) of dye-sensitized solar cells (DSSC) fabricated using these nanoparticles. A postulated reaction mechanism concerning the role of D-sorbitol in the formation of rutile and anatase was proposed. Fourier-transform infrared spectroscopy, 13C NMR spectroscopy, and dynamic light scattering analyses were used to better understand the interaction between the Ti precursor and D-sorbitol. The crystal phase and size of the synthesized TiO2 nanocrystallites as well as photovoltaic performance of the DSSC were examined using X-ray diffraction, Raman spectroscopy, field-emission scanning electron microscopy, high-resolution transmission electron microscopy, and photocurrent density-applied voltage spectroscopy measurement techniques. The DSSC fabricated using the anatase TiO2 nanoparticles synthesized in the presence of D-sorbitol, exhibited an enhanced η (6%, 1.5-fold improvement) compared with the device fabricated using the rutile TiO2 synthesized without D-sorbitol.

Sputtering and sulfurization-combined synthesis of a transparent WS2 counter electrode and its application to dye-sensitized solar cells

In this work, continuous and large-area tungsten sulfide (WS2) films, deposited by radio frequency sputtering followed by a sulfurization process, were applied as a low-cost platinum (Pt)-free counter electrode (CE) for dye-sensitized solar cells (DSSCs). The composition and structure of WS2 films were confirmed using X-ray diffraction, field-emission scanning electron microscopy, Raman spectroscopy and X-ray photoemission spectroscopy techniques. The WS2 CE was phase pure and considerably transparent. The cyclic voltammetry, electrochemical impedance spectroscopy and Tafel curve showed that the WS2 CE possesses high electrocatalytic activity and fast reaction kinetics for the reduction of tri-iodide to iodide, which can be attributed to its inherent catalytic property. Finally, TiO2-based DSSC with an optimized WS2 CE (sputtered for 10 min) showed as high as 6.3% power conversion efficiency, which was comparable to the performance of DSSC with a Pt-based CE (6.64%). Our study demonstrated the feasibility to develop low-cost, transparent, catalytically active, stable and abundant metal chalcogenide catalysts by an RF sputtering method to replace Pt CE for photovoltaic application.

Natural Carbonized Sugar as a Low-Temperature Ammonia Sensor Material: Experimental, Theoretical, and Computational Studies

Carbonized sugar (CS) has been synthesized via microwave-assisted carbonization of market-quality tabletop sugar bearing in mind the advantages of this synthesis method, such as being useful, cost-effective, and eco-friendly. The as-prepared CS has been characterized for its morphology, phase purity, type of porosity, pore-size distribution, and so on. The gas-sensing properties of CS for various oxidizing and reducing gases are demonstrated at ambient temperature, where we observe good selectivity toward liquid ammonia among other gases. The highest ammonia response (50%) of a CS-based sensor was noted at 80 °C for 100 ppm concentration. The response and recovery times of the CS sensor are 180 and 216 s, respectively. This unveiling ammonia-sensing study is explored through a plausible theoretical mechanism, which is further well-supported by computational modeling performed using density function theory. The effect of relative humidity on the CS sensor has also been studied at ambient temperature, which demonstrated that the minimum and maximum (20-100%) relative humidity values revealed 16 and 62% response, respectively.

Low-temperature solution-processed Zn-doped SnO2 photoanodes: enhancements in charge collection efficiency and mobility

An increase in charge collection efficiency and charge mobility from 78 to 89% and 0.02 to 0.04 cm2 V−1 s−1, respectively, in low-temperature solution-processed Zn-doped SnO2 photoanodes resulted in a two-fold enhancement in power conversion efficiency (PCE) as compared to Zn free SnO2 photoanodes in dye-sensitized solar cells (DSSCs).

Room-temperature successive ion transfer chemical synthesis and the efficient acetone gas sensor and electrochemical energy storage applications of Bi2O3 nanostructures

The acetone gas sensor and electrochemical supercapacitor applications of bismuth oxide (Bi2O3) nanostructures, synthesised using a facile and cost-effective quaternary-beaker mediated successive ion transfer wet chemical method and deposited onto soda-lime-glass (SLG) and Ni-foam substrates, respectively, are explored. The as-deposited Bi2O3 nanostructures on these substrates exhibit polycrystalline nature and a slight change in their surface appearance (i.e. upright-standing nanoplates on SLG and a curvy nanosheet structure on Ni-foam), suggesting the importance of the deposition substrate in developing Bi2O3 morphologies. The Bi2O3 nanoplate gas sensor on the SGL demonstrated a room temperature sensitivity of 41%@100 ppm for acetone gas, whereas the nanosheet structure of Bi2O3 on the Ni-foam elucidated a specific capacitance of 402 F g−1 at 2 mA cm−2, long-term cyclability, and rate capability with moderate chemical and environmental stability in a 6 M KOH electrolyte solution. The Bi2O3//graphite pencil-type asymmetric supercapacitor device revealed a specific capacitance as high as 43 F g−1, and an energy density of 13 W h kg−1 at 793 W kg−1 power density, turning a light emitting diode ON, with considerable full-brightness light intensity, during the process of discharging.

High Current Density Cation-exchanged SnO2-CdSe/ZnSe and SnO2-CdSe/SnSe Quantum-dot Photoelectrochemical Cells

Research on the combination of low and high-bandgap energy materials through an ion-mediated chemical transformation of the nanostructure of one material into another, especially metal chalcogenide quantum dot (QD) solar cells plays a very important role in the fast charge transformation process with high power conversion efficiencies (PCE) by reducing surface charge recombinations. Based on a coordination chemistry approach, the present study demonstrates the importance of cation-exchange process in developing bandgap engineering of tin oxide–cadmium selenide (SnO2–CdSe) with zinc selenide (ZnSe) and tin selenide (SnSe) to form SnO2–CdSe/ZnSe and SnO2–CdSe/SnSe electrodes, respectively. Experimental conditions are optimized from optical and photovoltaic performances. Our best performing cation-exchange interface-modified photoelectrochemical devices, i.e., SnO2–CdSe/ZnSe and SnO2–CdSe/SnSe have achieved improvements of 21% and 28%, respectively, in their PEC values, i.e., 3.78% and 4.41% with remarkable current densities of 19.82 and 28.40 mA cm−2 when compared with SnO2–CdSe (1.63% and 9.74 mA cm−2). This is due to (a) the fast transfer of photo-generated electrons from the CdSe QD sensitizer to SnO2 photoanode by engineering a synergistically favourable band gap and (b) mitigation of a reverse photogenerated electron flow in the presence of a high band gap buffer ZnSe/SnSe layer, which would otherwise cause excessive recombinations. A simple cation-exchange interface modification process can, in general, pave the way for improving the performance of QD-based solar cells.