Perovskite Variant Research Articles

Antimony doped Cs2SnCl6 with bright and stable emission

Lead halide perovskites, with high photoluminescence efficiency and narrow-band emission, are promising materials for display and lighting. However, the lead toxicity and environmental sensitivity hinder their potential applications. Herein, a new antimony-doped lead-free inorganic perovskites variant Cs2SnCl6:xSb is designed and synthesized. The perovskite variant Cs2SnCl6:xSb exhibits a broadband orange-red emission, with a photoluminescence quantum yield (PLQY) of 37%. The photoluminescence of Cs2SnCl6:xSb is caused by the ionoluminescence of Sb3+ within Cs2SnCl6 matrix, which is verified by temperature dependent photoluminescence (PL) and PL decay measurements. In addition, the all inorganic structure renders Cs2SnCl6:xSb with excellent thermal and water stability. Finally, a white light-emitting diode (white-LED) is fabricated by assembling Cs2SnCl6:0.59%Sb, Cs2SnCl6:2.75%Bi and Ba2Sr2SiO4: Eu2+ onto the commercial UV LED chips, and the color rendering index (CRI) reaches 81.

Low-energy paths for octahedral tilting in inorganic halide perovskites

Instabilities relating to cooperative octahedral tilting is common in materials with perovskite structures, and in particular in the sub class of halide perovskites. In this work, the energetics of octahedral tilting in the inorganic metal halide perovskites CsPbI$_3$ and CsSnI$_3$ are investigated using first-principles density functional theory calculations. Several low energy paths between symmetry equivalent variants of the stable orthorhombic (\textit{Pnma}) perovskite variant are identified and investigated. The results are in favor of the presence of dynamic disorder in the octahedral tilting phase transitions of inorganic halide perovskites. In particular, one specific type of path, corresponding to an out-of-phase "tilt switch", is found to have significantly lower energy barrier than the others, which indicates the existence of a temperature range where the dynamic fluctuations of the octahedra follow only this type of path. This could produce a time averaged structure corresponding to the intermediate tetragonal (\textit{P4/mbm}) structure observed in experiments. Deficiencies of the commonly employed simple one-dimensional "double well" potentials in describing the dynamics of the octahedra are pointed out and discussed.

Lead free, air stable perovskite derivative Cs2SnI6 as HTM in DSSCs employing TiO2 nanotubes as photoanode

Cs2SnI6 is an air-stable and non-toxic perovskite variant photovoltaic material which exhibits p-type conductivity under doped conditions. In this work, we report the synthesis and stability studies of Cs2SnI6 towards its application as a solid-state Hole Transport Material (HTM) in Titania Nanotube (TNT) based Dye Sensitized Solar Cells (DSSCs). Cs2SnI6 crystals were synthesized using precipitation method and its stability was assessed using X-ray diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS) and Thermogravimetric Analysis (TGA). Cs2SnI6 doped with SnI2 was deposited onto the TNT photo-anode as the HTM layer through dip coating. Deposition time was varied to obtain a continuous layer of Cs2SnI6 HTM over TNT photo-anode and cell characteristics were studied. We were able to fabricate air stable, all solid-state solar cells with a Jsc of 6 mA/cm2, Voc of 536 mV and PCE of 1.3%. The study propounds contemporary analysis on Sn based perovskite systems, in the field of DSSCs.

Zero-Dimensional Organic-Inorganic Perovskite Variant: Transition between Molecular and Solid Crystal.

Low-dimensional organic-inorganic halide perovskites (OIHPs) have attracted intense interest recently for photovoltaic applications, due to their markedly high chemical stability as compared to the widely studied three-dimensional (3D) counterparts. However, low-dimensional OIHPs usually give much lower device performance than the 3D OIHPs. In particular, for the zero-dimensional (0D) OIHPs, it is believed that the strong intrinsic quantum-confinement effects can lead to extremely low carrier motility, which can severely limit the photovoltaic performance. Herein, we predict a new family of 0D perovskite variants that, surprisingly, exhibit outstanding optoelectronic properties. We show that the "atypical" carrier mobility of these new 0D perovskites is attributed to the strong electronic interaction between neighboring octahedrons in the crystal. These findings also suggest a new materials design strategy for resolving the low-performance issue commonly associated with the low-dimensional OIHPs for photovoltaic applications.

Highly Efficient Blue‐Emitting Bi‐Doped Cs2SnCl6 Perovskite Variant: Photoluminescence Induced by Impurity Doping

AbstractLead halide perovskites show excellent optoelectronic properties but are unsatisfactory in terms of stability and toxicity. Herein, bismuth (Bi)‐doped lead‐free inorganic perovskites Cs2SnCl6:Bi are reported as blue emissive phosphors. Upon Bi doping, the originally nonluminous Cs2SnCl6 exhibits a highly efficient deep‐blue emission at 455 nm, with a Stokes shift of 106 nm and a high photoluminescence quantum yield (PLQY) close to 80%. Hybrid density functional theory calculations suggest the preferred formation of [BiSn+VCl] defect complex, which is believed to be responsible for the optical absorption and the associated blue emission. The Cs2SnCl6:Bi also shows impressive thermal and water stability due to its inorganic nature and the formation of protective BiOCl layer. White light‐emitting diodes (LEDs) are constructed using Cs2SnCl6:Bi and commercial yellow phosphors combined with commercial UV LED chips, giving the Commission Internationale de I'Eclairage (CIE) color coordinates of (0.36, 0.37). This work represents a significant step toward the realization of highly efficient, stable, and environmentally benign next‐generation solid‐state lighting.

Optical and Electrical Properties of Perovskite Variant (CH3NH3)2SnI6

In recent years, lead halide perovskites have emerged as excellent photovoltaic materials for solar power generation. However, because they are toxic and chemically unstable in air, lead-free perovskites are also being investigated. In this study, the perovskite variant (CH3NH3)2SnI6 was studied. Polycrystalline films of (CH3NH3)2SnI6 were prepared using the thermal evaporation method. The films had a direct band gap of 1.81 eV with a strong absorption coefficient of ∼7 × 104 cm–1. In addition, the films were n-type with a carrier concentration of ∼2 × 1015 cm–3 and an electron mobility of ∼3 cm2 V–1 s–1. Moreover, the conductivity was increased by a factor of 4 under simulated solar illumination (100 mW cm–2). These results indicate that (CH3NH3)2SnI6 is a lead-free optical semiconductor suitable for solar cell applications.

The thermal stability and consolidation of perovskite variant Cs2SnCl6 using spark plasma sintering

AbstractDefect perovskites, a category of air and moisture stable perovskite molecular salts, have gained attention for photovoltaics in the search of alternatives to the organic lead‐based photovoltaics which show exceptional photovoltaic performance but suffer significant environmental instability and toxicity of Pb. Defect perovskites also have exceptional structural flexibility and diverse crystal chemistry, and thus, display potentials as host phases for incorporating high amounts of halides such as iodine and chorine. In this study, pure Cs2SnCl6, a lead‐free defect perovskite variant, was synthesized through a solution‐based route that produced particles ranging from 200 to 500 nm. The thermal stability of the as‐synthesized Cs2SnCl6 powders was investigated using thermogravimetric analysis (TGA), demonstrating stability up to 615°C, above which a phase decomposition occurs leading to the loss of constituent component of SnCl4. Consolidation of Cs2SnCl6 into dense pellets (≥94% theoretical density) was achieved via spark plasma sintering (SPS) at a low sintering temperature of 350°C. X‐ray diffraction confirms no phase decomposition in the SPS‐densified perovskite pellets as a result of rapid consolidation of the SPS sintering at a short duration and lower temperature, and the TGA analysis suggest a comparable thermal stability up to 627°C for the densified pellet, slightly better than the as‐synthesized powders. The thermal diffusivity of Cs2SnCl6 at room temperature was determined as 0.388 mm2·s−1 by laser flash measurement. This work further discussed the potential applications of the SPS‐densified Cs2SnCl6 beyond perovskite photovoltaics, introducing potential nuclear separations and waste forms for chlorine.

The air and thermal stabilities of lead-free perovskite variant Cs2SnI6 powder

Cs2SnI6, as an inorganic lead-free perovskite variant, is regarded as a more environment friendly photovoltaic material than methylammonium lead iodide perovskite. However, its air and thermal stabilities still remain unclear. In this paper, Cs2SnI6 powders were synthesized via a chemical bath deposition method. The crystalline phases, morphologies, and vibrational properties were investigated. Moreover, its phase and morphology can retain in air with high relative humidity over a week even a month. The thermal stability measurements indicate Cs2SnI6 is stable up to 270°C and then decomposes to CsI and SnI4. These results should pave the way for further application of Cs2SnI6 for more stable solar cells.

Plasmonic Solar Cells: From Rational Design to Mechanism Overview.

Plasmonic effects have been proposed as a solution to overcome the limited light absorption in thin-film photovoltaic devices, and various types of plasmonic solar cells have been developed. This review provides a comprehensive overview of the state-of-the-art progress on the design and fabrication of plasmonic solar cells and their enhancement mechanism. The working principle is first addressed in terms of the combined effects of plasmon decay, scattering, near-field enhancement, and plasmonic energy transfer, including direct hot electron transfer and resonant energy transfer. Then, we summarize recent developments for various types of plasmonic solar cells based on silicon, dye-sensitized, organic photovoltaic, and other types of solar cells, including quantum dot and perovskite variants. We also address several issues regarding the limitations of plasmonic nanostructures, including their electrical, chemical, and physical stability, charge recombination, narrowband absorption, and high cost. Next, we propose a few potentially useful approaches that can improve the performance of plasmonic cells, such as the inclusion of graphene plasmonics, plasmon-upconversion coupling, and coupling between fluorescence resonance energy transfer and plasmon resonance energy transfer. This review is concluded with remarks on future prospects for plasmonic solar cell use.

Octahedral rotation patterns in strainedEuFeO3and otherPbnmperovskite films: Implications for hybrid improper ferroelectricity

The control of octahedral rotations in perovskite heterostructures is an emerging strategy for inducing new functionality as evidenced by recent predictions of improper ferroelectricity, polar metals, and multiferroics. Many of these predictions are predicated on the presence of a specific rotation pattern (${a}^{-}\phantom{\rule{0}{0ex}}{a}^{-}\phantom{\rule{0}{0ex}}{c}^{+}$) in superlattices that exhibit the orthorhombic ($P\phantom{\rule{0}{0ex}}b\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}m$) perovskite structural variant. The authors use synchrotron diffraction to measure the octahedral rotation patterns in strained ferrite, manganite, and gallate perovskite films finding that compressive strain strongly favors ${a}^{+}\phantom{\rule{0}{0ex}}{a}^{-}\phantom{\rule{0}{0ex}}{c}^{-}$ rotation patterns and tensile strain weakly favors ${a}^{-}\phantom{\rule{0}{0ex}}{a}^{-}\phantom{\rule{0}{0ex}}{c}^{+}$ structures. In contrast, films grown on orthorhombic substrates exhibit the same rotation pattern orientation as the substrate, even for epitaxial conditions where strain would favor the opposite structural orientation. The results indicate that substrate imprinting is a more robust method than strain for controlling the rotation pattern in $P\phantom{\rule{0}{0ex}}b\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}m$-type perovskite films, a finding that should enable more efficient experimental pursuits of rotation-driven ferroic states in oxide heterostructures.

Ligand-Hole in [SnI6] Unit and Origin of Band Gap in Photovoltaic Perovskite Variant Cs2SnI6

Abstract Cs2SnI6, a variant of perovskite CsSnI3, is gaining interest as a photovoltaic material. Based on a simple ionic model, it is expected that Cs2SnI6 is composed of Cs+, I−, and Sn4+ ions and that the band gap is primarily made of occupied I− 5p6 valence band maximum (VBM) and unoccupied Sn4+ 5s conduction band minimum (CBM) similar to SnO2. In this work, we performed density functional theory (DFT) calculations and revealed that the real oxidation state of the Sn ion in Cs2SnI6 is +2 similar to CsSnI3. The +2 oxidation state of Sn originates from 2 ligand holes (L+) in the [SnI6]2− octahedron unit, where the ligand [I6] cluster has the apparent [I66−L+2]4− oxidation state, because the band gap is formed mainly by occupied I 5p VBM and unoccupied I 5p CBM. The +2 oxidation state of Sn and the band gap originate from the intracluster hybridization and stabilized by the strong covalency of the Sn–I bonds.

Support-Promoted Stabilization of the Metastable PZT Pyrochlore Phase by Epitaxial Thin Film Growth

Thin films of lead zirconium titanium oxide with the Zr/Ti ratio close to 52/48 have been grown by pulsed laser deposition on epitaxial (100)CeO2 buffered R-plane sapphire substrates. Instead of the expected perovskite structure, these films are pure cubic metastable pyrochlore phase. From X-ray diffraction in θ–2θ mode and θ-scans it appears than the films are fully {100} oriented with a mosaicity in the range 0.8°–0.9°. In-plane characterizations, including RHEED photographs, electron-channeling patterns, XRD ϕ-scans, and near grazing incidence XRD, are indicative of high-quality epitaxial growth, cube-on-cube, on the CeO2 sublayer. RBS analyses show that increasing the deposition temperature in the range 560–650°C does not affect the Zr/Ti ratio, while the lead content drops significantly from Pb/(Zr+Ti)=0.7 to 0.3 (a stoichiometry close to the composition of “Pb(Zr0.52Ti0.48)3O7”); simultaneously, the unit-cell constant decreases monotically from 10.40 to 10.15 Å. A comparison with results obtained on a variety of other substrates suggests that the driving force that imposes the growth of the pyrochlore phase at the expense of the perovskite-like one is not related to the misfit, but to the nature of the interface at the atomic scale, due to the close structural relations between fluorite and pyrochlore. This hypothesis is confirmed by the obtention of the usual perovskite variant when a (111)CeO2 sublayer is used.

The First Oxostannate(II): K2Sn2O3

A new SnIIO compound, the first oxostannate(II) of defined structure, has been obtained as brownish‐yellow single crystals. X‐Ray structure analysis reveals a complicated perovskite variant (Sn1O3Sn2 double layers) in which half of the anions are missing in a regular manner.