Hybrid perovskites have attracted much attention as a promising photovoltaic material in the past few years. Typically, these hybrid perovskites such as methyl ammonium lead halides (MAPbX3) undergo dimensionality reduction from three-dimensional (3D) to zero-dimensional (0D), and finally to PbX2, upon continuous moisture exposure. Our current study shows that 0D-perovskite-related structures exhibit a reversible transformation from a transparent state to a colored 3D state upon exposure to humidity. Fluorescence imaging of individual microcrystals reveals that the structural phase transition could be visualized in the solid state, wherein the crystals transform into cubic crystals. The plausible reason for this transformation is proposed to be a dynamic dissolution and recrystallization of the excess methyl ammonium halide with varying humidity. The thermal and moisture stability are found to be greatly enhanced in the transformed 3D perovskite. Excellent device stability is also demonstrated when the devices are kept under moist (∼70% RH) conditions.
Structural stability, electronic structure and optical properties of CH3NH3BaI3 hybrid perovskite is examined from theory as well as experiment. Solution-processed thin films of CH3NH3BaI3 exhibited a high transparency in the wavelength range of 400 nm to 825 nm (1.5 eV to 3.1 eV for which the photon current density is highest in the solar spectrum) which essentially justifies a high bandgap of 4 eV obtained by theoretical estimation. Also, the XRD patterns of the thin films match well with the {00l } peaks of the simulated pattern obtained from the relaxed unit cell of CH3NH3BaI3, crystallizing in the I4/mcm space group, with lattice parameters, a = 9.30Å, c = 13.94Å. Atom projected density of state and band structure calculations reveal the conduction and valence band edges to be comprised primarily of Barium d -orbitals and Iodine p-orbitals, respectively. The larger band gap of CH3NH3BaI3 compared to CH3NH3PbI3 can be attributed to the lower electro-negativity coupled with the lack of d -orbitals in the valence band of Ba 2+ . A more detailed analysis reveals the excellent chemical and mechanical stability of CH3NH3BaI3 against humidity, unlike its lead halide counterpart, which degrades under such conditions. We propose La to be a suitable dopant to make this compound a promising candidate for transparent conductor applications, especially for all perovskite solar cells. This claim is supported by our calculated results on charge concentration, effective mass and vacancy formation energies.PACS numbers: 81.10.Dn, 61.50.Ah, 61.10.Nz, 42.70.Qs, Recently, compounds in the organic-inorganic halide perovskite family (AB X 3 : A is an organic cation, B is an inorganic cation, and X is a halide element) have garnered a lot of attention in the solar photovoltaic community. This is due to their superior optoelectronic properties, easy synthesis techniques and variety of compounds that can be obtained via simple substitutions of the A, B and X ions. Specifically, solar cells, with (CH 3 NH 3 ) + as the A cation and Pb 2+ as the B cation, have shown a rapid growth in the solar-to-electricity power conversion efficiency.1-5 The lead halide perovskite solar cell was first introduced by Kojima et al in 2009, wherein it was used in a dye-sensitized solar cell architecture.6 Much of the research in recent times has focused on solid-state cells with different architectures, hole transport layers, compositional engineering, and synthesis techniques.1,3,7-10 Even then, there are some caveats associated with the various components of the CH 3 NH 3 PbX 3 -based solar cells: the stability of the absorber material in ambient conditions and the presence of Pb to name a couple. Active research to address these problems is being conducted worldwide through suitable replacements to both the CH 3 NH 3 and Pb cations.Tunability of the properties by changing the constituent elements gives this class of material more scope of research and applicability.11-13 Such tunability in the bandgap has been observed in the oxide perovskites, wher...
1% La doped BaSnO3 thin films of different thicknesses, ranging from 15 to 300 nm, were obtained on single crystal Lanthanum Aluminate-Strontium Aluminate Tantalate [LSAT(001)] substrates via Pulsed Laser Deposition. The films grow epitaxially on these substrates (cube-on-cube epitaxy) and are almost relaxed with a strain of ≈0.51% for 300 nm films. All films show n-type conducting behavior with their conductivity varying from 65.36 S cm−1 to 465.11 S cm−1 as the thickness of the film is increased. Low temperature carrier concentration measurements indicate that the films are degenerate semiconductors. Films with a thickness ≥30 nm exhibit metal to semiconductor transition (MST) at low temperatures. Temperature dependent resistivity analysis of the films shows evidence of electron-electron interaction rather than weak localization as the governing transport mechanism below MST. The transition temperature shifts toward lower values at higher thicknesses, strengthening the metallic transport in such films.
Highly conducting and transparent thin films of La x Ba1 − x SnO3 (x = 0, 0.01 and 0.05) were grown on quartz substrates via pulsed laser deposition. Conductivity increases in orders of magnitude upon vacuum annealing of the as–deposited films. This is attributed to the significant enhancement in carrier concentration due to the increased oxygen vacancy defects (V O ∙ ∙ ). Enhanced carrier concentration improves the metallicity in the films at room temperature. Metal to semiconductor transition (MST) is observed in the films with n e ⩾ 1019 cm−3 at low temperatures. The MST shifts towards absolute zero temperature as the carrier concentration in the film increases. Low–temperature resistivity analysis suggests that the charge transport is mainly governed by strong electron–electron interaction. UV–Vis spectroscopy confirms a 60%–80% transmittance in the visible range (400–800 nm) for all the films. Due to the large change in carrier concentration, Burstein Moss (BM) shift is observed, and the bandgap ranges between 3.65–3.98 eV. The effective mass of electron and refractive index estimated from the BM shift and transmittance are found to be 0.6 m e and 2, respectively.
Artificial synapses, such as ferroelectric field‐effect transistors, aspire the brain‐like computation in real life and are likely to replace conventional computing methods in the future. Amorphous SiZnSnO (a‐SZTO)‐based ferroelectric field‐effect transistor is fabricated using the organic poly(vinylidene fluoride‐trifluoroethylene) P(VDF‐TrFE) ferroelectric gate insulating layer. First, the ferroelectric properties of P(VDF‐TrFE) are analyzed depending on the crystallization temperature for artificial synaptic transistor applications. The ferroelectricity becomes prominent with the evolution of the β‐phase till 140 °C and degrades thereafter. The a‐SZTO‐based ferroelectric field‐effect transistors employing P(VDF‐TrFE) show anticlockwise hysteresis, typical for a ferroelectric field‐effect transistor. The nonlinearity for the potentiation and depression and the dynamic range is confirmed to be increased with higher β‐phase concentration. The rise in the concentration is related to the elevated thermodynamic stability of the β‐phase between curie temperature and the melting point. Utilizing the parameters obtained from the a‐SZTO‐P(VDF‐TrFE) synaptic transistor, the simulation studies exhibit a high recognition rate of 86.8%, which makes it a promising candidate for artificial intelligence applications.
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