Towards increasing the stability of perovskite solar cells, the addition of Cs is found to be a rational approach. Recently triple cation based perovskite solar cells were found to be more effective in terms of stability and efficiency. Heretofore they were unexplored, so we probed the Cs/MA/FA (cesium/methyl ammonium/formamidinium) cation based perovskites by X-ray photoelectron spectroscopy (XPS) and correlated their compositional features with their solar cell performances. The Cs content was found to be optimum at 5%, when incorporated in the (MAFA)Pb(IBr) lattice, because the corresponding device yielded the highest fill factor compared to the perovskite without Cs and with 10% Cs. XPS studies distinctly reveal how Cs aids in maintaining the expected stoichiometric ratios of I : Pb, I : N and Br : Pb in the perovskites, and how the valence band (VB) edge is dependent on the Cs proportion, which in turn governs the open circuit voltage. Even at a low content of 5%, Cs resides deep within the absorber layer, and ensures minimum distortion of the VB level (compared to 0% and 10% Cs perovskites) upon Ar sputtering, thus allowing the formation of a stable robust material that delivers excellent solar cell response. This study which brings out the role of Cs is anticipated to be of paramount significance to further engineer the composition and improve device performances.

A molybdenum dioxide/multiwalled carbon nanotubes (MoO2/MWCNT) hybrid composed of spherical flowerlike nanostructures of MoO2, interconnected by MWCNTs has been prepared by a one-step hydrothermal route. The growth of MoO2 nanoparticles into spherical floral shapes with a monoclinic crystalline structure is steered by the dioctyl sulfosuccinate surfactant. The one-dimensional electron transport pathways provided by MWCNTs, which are in direct contact with MoO2 nanostructures, impart an enhanced reversible lithium storage capacity (1143 mA h g(-1) at a current density of 100 mA g(-1) after 200 cycles), high rate capability (408 mA h g(-1) at a high C-rate of 1000 mA g(-1)) and good cycling stability to the MoO2/MWCNT hybrid relative to neat MoO2. Surface potential mapping of the electrodes by Kelvin probe force microscopy, revealed a lower localized work function for the MoO2/MWCNT hybrid as compared to the neat oxide. This makes the MoO2/MWCNT hybrid more easily oxidizable than neat MoO2. Such a distinctive topology achieved for the MoO2/MWCNT hybrid, wherein the MWCNTs prevent the agglomeration of MoO2 nanostructures and thus preserve good electrical connectivities, makes it different in terms of both morphology and performance from all previously reported MoO2-based anode materials to date.

We report a facile method to synthesize poly(3,4-ethylenedioxythiophene) (PEDOT) films at room temperature in a waterproof ionic liquid, 1-ethyl-3-methylimidazolium bis(perfluoroethylsulfonyl)imide (EMIPFSI), by electropolymerization. The ionic liquid leads to the formation of randomly oriented nanofibers and particles confined to submicrometer-sized domains in the film microstructure. X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray (EDX) studies provide information about the intercalation of the cation apart from the reported anion in the polymer film, and on how the imidazolium ion controls the growth of PEDOT nanostructures.

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As-deposited sol-gel derived amorphous tungsten oxide films transform into nanostructured films with an interconnected framework of grains and pores and a dominant triclinic crystalline phase upon annealing at 250°C. Transmission electron microscopy and scanning electron microscopy images clearly reveal the annealing-induced microstructural evolution for the film. Subsequent to lithium intercalation, the film annealed at 250°C shows quasi-reversible structural changes, as ascertained by X-ray diffraction and Fourier transform infrared spectral data. Dynamic transmission modulation for film revealed a high optical modulation of 72% ͑ = 650 nm͒ and a coloration efficiency maximum of 132 cm 2 C −1 at 800 nm under a lithium intercalation level of x = 0.20. X-ray photoelectron spectroscopy of the W 4f core levels demonstrated a progressive increase in the W 5+ content at the expense of W 6+ proportion as the insertion coefficient was raised from 0 to 0.25, with 0.20 as the threshold value above which the W 5+ content exceeds the W 6+ proportion. A new W 4+ state also appears which acts to lower the coloration efficiency for x ജ 0.22. The presence of charged oxygen interstitials in the vicinity of electrochemically active tungsten sites is also responsible for the coloration efficiency decline at high ion insertion levels.

Composite thin films of poly(3,4-ethylenedioxythiophene) (PEDOT)-enwrapped functionalized multiwalled carbon nanotubes (MWCNTs) have been synthesized over multiple length scales by electropolymerization of the monomer without the use of any other supporting electrolyte. The functionalized MWCNTs are incorporated into the positively charged polymer deposit as counterions during oxidative electropolymerization. The morphology, electrochemistry, and electrochromism of the PEDOT-MWCNT films have been compared with those of control PEDOT films doped by triflate ions. Such a comparison enabled us to demonstrate the profound effect of MWCNTs as counterions, realized in terms of better electropolymerization rate, higher conductivity, faster color-bleach kinetics, higher charge storage capacity, and substantially amplified coloration efficiency (eta = 414 cm(2) C(-1), lambda(max) = 575 nm, E = -1.5 V) in comparison to the values of eta reported to date for PEDOT. The strong interaction between the polymer and MWCNTs, the interconnected nanotubular structures, and the porous framework of the film allow facile charge transport and larger ion uptake during redox switching. Electrochemical investigations on devices based on PEDOT-MWCNT and control PEDOT films established the practical utility of PEDOT-MWCNT films as they show lower charge-transfer resistance, higher diffusional capacitance, and a much smaller amplitude of impedance as compared to control PEDOT films.

A potential driven self-assembly of sodium dodecyl sulfate/tungsten oxide aggregates at the electrolyte-electrode interface followed by template extraction and annealing yielded mesoporous thin films of electrochromic tungsten oxide (WO(3)). Electron microscopy images revealed that the films are characterized by a hitherto unreported hybrid structure comprising nanoparticles and nanorods with a tetragonal crystalline phase of WO(3) with the measured lattice parameters: a = 0.53 nm and c = 0.37 nm. In addition to pentagonal voids characteristic of the tetragonal WO(3) phase at the lattice scale, open channels and pores of 5-10 nm in diameter lie between the nanoparticles, which cumulatively promote rapid charge transport through the film. This resulted in colouration efficiency (η(max)∼90 cm(2) C(-1) at λ = 900 nm) and switching kinetics (colouration time =  3 s and bleaching time =  2 s for a 50% change in transmittance) higher and faster than previously reported values for mesoporous WO(3) films. Repetitive cycling between the clear and blue states has no deleterious effect on the electrochromic performance of the film, which is suggestive of its potential as a cathode in practical electrochromic windows.