Tin oxide as an emerging electron transport medium in perovskite solar cells

Electron transport medium (ETM) is one of the most important components determining the photovoltaic performance of organic-inorganic halide perovskite solar cells (PSCs). Among the metal oxide semiconductors, anatase (TiO2) is the most common material used as ETM in PSCs to facilitate charge collection as well as to support a thin perovskite absorber layer. Production of conductive crystalline TiO2 requires relatively higher temperatures (400–500 °C) which limits its application to glass substrates coated with fluorine tin oxide (FTO) as other tin oxides (e.g. indium tin oxide) degrade at temperatures above 300 °C. Furthermore, this renders it unsuitable for flexible devices, often based on low-temperature flexible plastic substrates. Pure tin oxide, one of the earliest metal oxide semiconductors, is often used in myriad electronic devices and has shown outstanding characteristics as an ETM in PSC systems. Thus, tin oxide can be considered a viable alternative to TiO2 due to its excellent electron mobility and higher stability than other alternatives such as zinc oxide. This review article gives a brief history of ETMs in PSC systems and reviews recent developments in the use of tin oxide in both pure and composite form as ETMs. Efficiencies of up to 21% have been reported in tin oxide based PSCs with photovoltages of up to ~1214 mV

Floristic diversity of Theog Forest Division, Himachal Pradesh, Western Himalaya

We provide a check list of the vascular plants of Theog Forest Division, Himachal Pradesh, Western Himalaya. Himachal Pradesh has been extensively surveyed in terms of flora by a large number of workers, albeit highly confined to prioritized areas. The floristic inventorization resulted in a total of 442 vascular plant species belonging to 311 genera and 117 families from an area of 512 km2. Out of these, 408 species belonged to Angiosperms, 7 to Gymnosperms and 27 to Pteridophytes. The predominant families among Dicotyledons were Asteraceae, Rosaceae and Lamiaceae. Among the Monocotyledons, the most represented family was Poaceae, followed by Liliaceae and Cyperaceae. Pinaceae and Pteridaceae were found to be the most represented families among the Gymnosperms and Pteridophytes, respectively. Species richness was highest in shrubberies, which formed an ideal habitat for many herbaceous species within different habitat types. Strategic eradication of weed species, especially obnoxious species such as Lantana camara and Parthenium hysterophorus is required for effective management in the area

Characterization of supercapacitive charge storage device using electrochemical impedance spectroscopy

In combination with an analogous circuit pattern, the electrochemical impedance (EIS) spectra aids in examining the physical origin of the different electrical components involved in the device. In this research, to illustrate the various physical processes taking place in energy-storing electrodes, the EIS spectra in the entire frequency area is divided into specific electrical elements such as resistors and capacitors with the help of Z view software and determined origin of their charge storage properties. The EIS spectra of activated carbon (AC) – TiO2 or MnO2 composites containing TiO2 in the range 5 – 20 wt% and nominal composition of MnO2 (5 wt% MnO2) are analyzed using the equivalent circuit fitting technique and the corresponding electrode parameters and performances are correlated

Hydrothermal syntheses of tungsten doped TiO 2 and TiO 2 /WO 3 composite using metal oxide precursors for charge storage applications

Synthesis of advanced functional materials through scalable processing routes using greener approaches is essential for process and product sustainability. In this article, syntheses of nanoparticles of titanium dioxide (TiO₂), tungsten trioxide (WO₃), WO₃-doped titanium dioxide (W-TiO₂) and TiO₂/WO₃ composite at hydrothermal conditions using corresponding metal oxide precursors are described. Electrochemical charge storage capabilities of the above materials are measured using cyclic voltammetry, charge-discharge cycling and electrochemical impedance spectroscopy in aqueous KOH electrolyte. The TiO₂ and the WO₃ nanoparticle showed a specific charge (Q) of ∼12 and ∼36 mA h g⁻¹ at a current density of 2 A g⁻¹ in 6 M KOH, respectively. The Q of TiO₂ increased upon W doping up to 25 mA h g−1 for 5 wt% W-TiO2 and the WO₃/TiO₂ composite showed the highest storage capability (Q ∼40 mA h g⁻¹). Changes in the charge storage capabilities of the doped and composite materials have been correlated to materials properties.Bhupender Pal acknowledges the Research & Innovation Department of Universiti Malaysia Pahang (http://ump.edu.my) for award of Postdoctoral Fellowship. This project is funded under Flagship Strategic Leap 3 of Universiti Malaysia Pahang (Grant Number # RDU 172201)

Exploration of Charge Storage Behavior of Binder-Free EDL Capacitors in Aqueous Electrolytes

Charge storage in electrochemical double-layer capacitors (EDLCs) is via the adsorption of electrolyte counterions in their positive and negative electrodes under an applied potential. This study investigates the EDLC-type charge storage in carbon nanotubes (CNT) electrodes in aqueous acidic (NaHSO4), basic (NaOH), and neutral (Na2SO4) electrolytes of similar cations but different anions as well as similar anions but different cations (Na2SO4 and Li2SO4) in a two-electrode Swagelok-type cell configuration. The physicochemical properties of ions, such as mobility/diffusion and solvation, are correlated with the charge storage parameters. The neutral electrolytes offer superior charge storage over the acidic and basic counterparts. Among the studied ions, SO42– and Li+ showed the most significant capacitance owing to their larger solvated ion size. The charge stored by the anions and cations follows the order SO42– > HSO4– > OH– and Li+ > Na+, respectively. Consequently, the CNT//Li2SO4//CNT cell displayed outstanding charge storage indicators (operating voltage ∼0–2 V, specific capacitance ∼122 F·g–1, specific energy ∼67 W h·kg–1, and specific power ∼541 W·kg–1 at 0.5 A·g–1) than the other cells, which could light a red light-emitting diode (2.1 V) for several minutes. Besides, the CNT//Li2SO4//CNT device showed exceptional rate performance with a capacitance retention of ∼95% at various current densities (0.5–2.5 A·g–1) after 6500 cycles. The insights from this work could be used to design safer electrochemical capacitors of high energy density and power density

Tailoring the charge storability of commercial activated carbon through surface treatment

Sustainability concerns in the electrochemical charge storage realm revitalized research on the electrochemical capacitors (ECs), or synonymously, supercapacitors (SCs), because of the renewability of their electrode materials and environmental benignity thereby, longer life cycle to improve materials circularity, and their inherent superior rate charging/discharging than batteries. As SCs store energy via the reversible adsorption of electrolyte ions on the electrode pores, maximizing the number of pores to accommodate the ions is the most desired way to improve the charge storability. In this regard, we report herewith a simple and facile approach for engineering the porosity of commercial activated carbon by refluxing it in nitric acid as a function of time; the BET surface area of the 72 h refluxed samples increased by 75 %. Charge storage properties of the modified electrodes are evaluated in a three-electrode system configuration in 1 M Na2SO4 electrolyte; a 75 % increase in the surface area led to an increase in specific capacitance over 110 % following a significant reduction in Warburg impedance. Besides, symmetric SC full cells were fabricated by varying the electrode mass between 3 and 14 mg·cm−2 in five steps. All the fabricated devices achieved a potential window of 1.8 V in 1 M Na2SO4. The highest mass loaded (∼14 mg·cm−2) device fabricated using the prepared material has delivered a maximum capacitance of ∼990 mF, the maximum areal capacitance of ∼494 mF·cm−2, an energy density of ∼13 mWh·cm−3, and a maximum power density of ∼2189 mW·cm−3. The device also maintained ∼97 % retention in capacitance with a remarkable coulombic efficiency of ∼97 % after 5000 cycles. The performance of the device is comparable with the commercial SCs used for low voltage DC hold-up applications such as embedded microprocessor systems. The procedure developed herewith supports easy recycling and reusing of the activation agent, and thereby reduces the release of toxic chemicals into the environment

Insights into the charge storage mechanism of binder-free electrochemical capacitors in ionic liquid electrolytes

Electrochemical capacitors (synonymously supercapacitors) working under an electrochemical double-layer charge storage mechanism (EDLC) are widely investigated because of their excellent power density and cycle life; however, their energy density is lower than those of lithium-ion batteries. Ionic liquids (ILs) are of great interest as electrolytes for EDLCs due to their wide operational voltage window. Here, we provide a systematic investigation on the influence of anions of ILs on the charge storage mechanism and electrochemical stability of EDLC electrodes. Two IL electrolytes, viz., [1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIMTFSI)], having similar cations but different anions and carbon nanotube (CNT) electrodes are chosen for this study. The CNT//BF4:TFSI//CNT-based device showed superior electrochemical performance (∼69 F•g-1 gravimetric specific capacitance, ∼949 W•kg-1 power density, and ∼139 Wh•kg-1 energy density at 0.5 A•g-1) to CNT//EMIMBF4//CNT and CNT//EMIMTFSI//CNT devices. The device using a mixture of BF4:TFSI (1:0.5) electrolytes has an operating voltage of 0-3.8 V and specific capacitance retention of ∼45% at 0.5 A•g-1 after 500 cycles. In the case of the IL mixture (BF4:TFSI), the combined anion structure and their properties play very crucial part in the improvement of the electrochemical performance of the CNT//BF4:TFSI//CNT device. The assembled Teflon Swagelok-type cell could light up green (3.3 V) and red (2.1 V) light-emitting diodes for more than 5 min

Characterization of electrochemical double layer capacitor electrode using self-discharge measurements and modeling

A simple protocol to characterize the electrochemical double layer capacitors (EDLCs) using self-discharge (open circuit discharge) data and a three-branch electrical model is presented. The method relies on recording the self-discharge data of EDLCs and using it to estimate the parametric values of the variables in the model (time constants, maximum voltage, resistances, and capacitances). Porous carbon and metal oxide electrodes in three choice electrolytes are used for the experiments and the simulations are performed using MATLAB Simulink platform. The simulated and experimental self-discharge data are in close agreement for the EDLC storage mode but not for the battery type storage. The results are further validated by simulating the galvanostatic charge discharge (GCD) cycling data and fitting them to the experimental GCD of the assembled devices with high accuracies. The model presented here thus enables determination of charge storage parameters as well as whether a device is capacitive from a single self-discharge data, thereby providing an excellent tool to characterize EDLCs for both academia and industry

Pseudocapacitive charge storage in thin nanobelts

This article reports that extremely thin nanobelts (thickness ~ 10 nm) exhibit pseudocapacitive (PC) charge storage in the asymmetric supercapacitor (ASC) configuration, while show battery-type charge storage in their single electrodes. Two types of nanobelts, viz. NiO–Co3O4 hybrid and spinal-type NiCo2O4, developed by electrospinning technique are used in this work. The charge storage behaviour of the nanobelts is benchmarked against their binary metal oxide nanowires, i.e., NiO and Co3O4, as well as a hybrid of similar chemistry, CuO–Co3O4. The nanobelts have thickness of ~ 10 nm and width ~ 200 nm, whereas the nanowires have diameter of ~ 100 nm. Clear differences in charge storage behaviours are observed in NiO–Co3O4 hybrid nanobelts based ASCs compared to those fabricated using the other materials—the former showed capacitive behaviour whereas the others revealed battery-type discharge behaviour. Origin of pseudocapacitance in nanobelts based ASCs is shown to arise from their nanobelts morphology with thickness less than typical electron diffusion lengths (~ 20 nm). Among all the five type of devices fabricated, the NiO–Co3O4 hybrid ASCs exhibited the highest specific energy, specific power and cycling stability

Floristic diversity of Theog Forest Division, Himachal Pradesh, Western Himalaya

We provide a check list of the vascular plants of Theog Forest Division, Himachal Pradesh, Western Himalaya. Himachal Pradesh has been extensively surveyed in terms of flora by a large number of workers, albeit highly confined to prioritized areas. The floristic inventorization resulted in a total of 442 vascular plant species belonging to 311 genera and 117 families from an area of 512 km2. Out of these, 408 species belonged to Angiosperms, 7 to Gymnosperms and 27 to Pteridophytes. The predominant families among Dicotyledons were Asteraceae, Rosaceae and Lamiaceae. Among the Monocotyledons, the most represented family was Poaceae, followed by Liliaceae and Cyperaceae. Pinaceae and Pteridaceae were found to be the most represented families among the Gymnosperms and Pteridophytes, respectively. Species richness was highest in shrubberies, which formed an ideal habitat for many herbaceous species within different habitat types. Strategic eradication of weed species, especially obnoxious species such as Lantana camara and Parthenium hysterophorus is required for effective management in the area