The supercapacitive charge storage as a function of electrolyte factors are critically reviewed.

The incessant demand for energy forces us to seek it from sustainable resources; and concerns on environment demands that resources should be clean as well. Metal oxide semiconductors, which are stable and environment friendly materials, are used in photovoltaics either as photoelectrode in dye solar cells (DSCs) or to build metal oxide p–n junctions. Progress made in utilization of metal oxides for photoelectrode in DSC is reviewed in this article. Basic operational principle and factors that control the photoconversion efficiency of DSC are briefly outlined. The d‐block binary metal oxides viz. TiO2, ZnO, and Nb2O5 are the best candidates as photoelectrode due to the dissimilarity in orbitals constituting their conduction band and valence band. This dissimilarity decreases the probability of charge recombination and enhances the carrier lifetime in these materials. Ternary metal oxide such as Zn2SnO4 could also be a promising material for photovoltaic application. Various morphologies such as nanoparticles, nanowires, nanotubes, and nanofibers have been explored to enhance the energy conversion efficiency of DSCs. The TiO2 served as a model system to study the properties and factors that control the photoconversion efficiency of DSCs; therefore, such discussion is limited to TiO2 in this article. The electron transport occurs through nanocrystalline TiO2 through trapping and detrapping events; however, exact nature of these trap states are not thoroughly quantified. Research efforts are required not only to quantify the trap states in mesoporous metal oxides but new mesoporous architectures also to increase the conversion efficiency of metal oxide‐based photovoltaics.

Polymorphs of 1D nanostructures of niobium pentoxide (Nb2O5) are synthesized by electrospinning. Pseudohexagonal (H−Nb2O5), orthorhombic (O−Nb2O5), and monoclinic (M−Nb2O5) structures of Nb2O5 are developed in this study by appropriate heat treatment. Morphological, structural, and electrochemical properties of these nanofibrous polymorphs are studied in detail. The H− and O− phases maintain the usual fibrous morphology, whereas the M− phase adopted a distorted nugget structure. These phases are evaluated for their application as cathode for lithium batteries. The M−Nb2O5 exhibits the highest capacity and better capacity retention compared to the other phases. The M−Nb2O5 delivers a specific capacity of 242(±3) and 218(±3) mAhg−1, cycled at a current of 50 mAg−1 in the voltage range, 1.0−2.6 V versus Li/Li+ at the end of second and 25th cycle, respectively. The electrospun M−Nb2O5 nuggets-based battery performs better than its particle/nanofiber counterpart and could be a cathode material of choice for 2 V due to the commercial viability of the electrospinning process and characteristics of the batteries developed herewith.

This article reviews the various hole transporting materials (HTMs) used in perovskite solar cells (PSCs) in achieving high photo conversion efficiency (PCE) and operational stability. The PSCs are the latest development in solution processable solar cells offering PCE (~22%) on a par with that of practically deployed silicon and thin film solar cells. HTMs and electron transporting materials (ETMs) are important constituents in PSCs as they selectively transport charges within the device, influence photovoltaic parameters, determine device stability and also influence its cost. This article critically approaches role of structure, electrochemistry, and physical properties of varied of choice of HTMs categorized diversely as small and long polymers, organometallic, and inorganic on the photovoltaic parameters of PSCs conceived in various device configurations. Achievements in tailoring the properties of HTMs to best fit for PSCs are detailed; a well designed HTM suppresses carrier recombination by facilitating the passage of holes but blocking electrons at the HTM/perovskite interface. Moreover, in many PSCs the HTM acts as the first line of defense to external degrading factors such as humidity, oxygen and photon dose, the extent of which depends on its hydrophobicity, permeability, and density.

A freestanding membrane composed of a nanofiber network of a graphene–polymer nanocomposite is fabricated by electrospinning and applied as an optical element in fiber lasers. The functionalization of graphene with conjugated organic molecules provides a handle for improving mechanical and thermal properties as well as tuning the optical properties. A small loading (0.07 wt%) of functionalized graphene enhances the total optical absorption of poly(vinyl acetate) (PVAc) by 10 times. The electrospun graphene–polymer nanocomposites exhibit wideband saturable absorbance for laser pulse shaping, and attain a larger modulation depth and smaller nonsaturable loss than single‐walled carbon nanotubes. The results show that electrospun graphene nanocomposites are promising candidates as practical and efficient photonic materials for the generation of ultrashort pulses in fiber lasers.

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understanding of device working mechanism whereas the notes below the line (red text) shows milestones towards scalability and stability. The text in black on the right (future) shows key questions that need to be addressed to completely understand the working of these devices for a commercially deployable device. For each Figure adapted in this timeline, a citation is added within the Figure itself. Crystal structure is reproduced with permission. [277] Copyright 2014, The Royal Society of Chemistry. Schematic of Al 2 O 3 is reproduced with permission. [7]

a Perovskite solar cells have attracted enormous interest since their discovery only a few years ago because they are able to combine the benefits of high efficiency and remarkable ease of processing over large areas. Whereas most of research has been carried out on glass, perovskite deposition and synthesis is carried out at low temperatures (o150 1C) to convert precursors into its final semiconducting form. Thus, developing the technology on flexible substrates can be considered a suitable and exciting arena both from the manufacturing view point (e.g. web processing, low embodied energy manufacturing) and that of the applications (e.g. flexible, lightweight, portable, easy to integrate over both small, large and curved surfaces). Research has been accelerating on flexible PSCs and has achieved notable milestones including PCEs of 15.6% on laboratory cells, the first modules being manufactured, ultralight cells with record power per gram ratios, and even cells made on fibres.Reviewing the literature, it becomes apparent that more work can be carried out in closing the efficiency gap with glass based counterparts especially at the large-area module level and, in particular, investigating and improving the lifetime of these devices which are built on inherently permeable plastic films. Here we review and provide a perspective on the issues pertaining progress in materials, processes, devices, industrialization and costs of flexible perovskite solar cells. Broader contextFor a number of years, solar cells had been considered as an inferior energy technology due to high cost -even in the renewable energy paradigm; however, more recently progress in materials processing and engineering of highly efficient and stable solar panels have helped them emerge as a frontline renewable energy technology with energy payback time that has been lowered from over a decade to a couple of years (at least in some parts of the world) during the last ten years. Commercial solar panels are typically manufactured on rigid platforms. Fabricating them on flexible substrates, such as transparent plastics and metallic foils, would enable effective harvesting of energy in a number of diverse areas from indoor electronics to automobiles and from building integrated photovoltaics to portable applications. Furthermore, it would open up web-based roll-to-roll fabrication conducive to massive throughputs. Solution processable perovskite solar cells offer promising opportunities towards this end. Being these cells the most efficient among the solution processable ones, with efficiency in their laboratory scale devices on par with the commercially available silicon and thin film counterparts, significant recent efforts devoted to their manufacturing on flexible substrates have seen efficiencies rise as high as 15.6% together with moderate stability. We approach the developments in this area by critically analyzing the factors affecting the final performance indicators such as efficiency, stability, and functionality and relate these to its proces...