Search

Abstract MAPbI3 is the most attractive perovskite, but toxicity and instability issues hinder its commercial applications. Stability can be improved by halide mixing; however, Pb‐free perovskites are designed to alleviate the toxicity and to enable green photovoltaics (PVs). To this end, MAPbI3‐xClx, FASnI3‐xClx and CsSbCl4 films are deposited by spay pyrolysis technique in atmospheric conditions. SEM images demonstrated that through this process, high quality film fabrication is possible. Color of the precursor solutions changes with stirring time. High crystallinity and existence of mixed‐phases are confirmed by XRD analysis. Compositions greatly impact the morphology and optical properties. Value of α is larger than 105 cm−1 for all films. Band gaps of FASnI3‐xClx and CsSbCl4 are 1.46 eV and 1.52 eV, which are more suitable for PVs, optoelectronic applications than MAPbI3‐xClx (Eg = 1.59 eV). The efficiency was obtained as 16.34%, 9.90%, and 13.08% for deposited MAPbI3‐xClx, FASnI3‐xClx, and CsSbCl4 films. The lower efficiency can further be enhanced by optimizing parameters, and in this study it was found as 20.78%, 11.93%, and 18.02%. Theoretical calculations show the films can easily produce O2 by a strong oxidation process. Thus, the favorable characteristics of FASnI3‐xClx and CsSbCl4 make alternative Pb‐free perovskites for PV, electronic, and optoelectronic applications.

Abstract In this paper we explain the temperature dependence of excitonic effective mass and charge carrier conduction mechanism occurs in CH3NH3PbI3−xClx thin films prepared by chemical dip coating (CDC), spray pyrolysis (Spray) and repeated dipping-withdrawing (Dipping). Hall Effect study confirmed that prepared CH3NH3PbI3−xClx samples are p-type semiconductor having carrier concentration of the order of ~ 1016 cm−3. The charge carrier mobility, mean free path and mean free life time were found to decrease with increasing temperature due to polaronic effect. The excitonic effective mass is estimated to (0.090–0.196)me and excitonic binding energy (15–33) meV, well consistent with Wannier-Mott hydrogenic model and the nature of exciton is likely to be Mott-Wannier type. From electrical measurement, it was observed that charge carrier conduction in CH3NH3PbI3−xClx is governed by migration of $${\mathrm{I}}^{-}$$ I - and CH3N $${\mathrm{H}}_{3}^{+}$$ H 3 + vacancies and vacancy-assisted diffusion processes depending on temperature.

In this paper, we have investigated the nonlinear optical response and theoretical efficiency of CH3NH3PbI3−xClx thin films from the optical transmission and reflection measurements. The dispersion of the complex refractive index is evaluated using the Wemple–DiDomenico single oscillator model. The oscillator energy (E0) of CH3NH3PbI3−xClx follows by an empirical relationship with optical bandgap (Eg) as E0 ≈ 2.41 Eg for chemical dip coating, spray, and E0 ≈ 1.63 Eg for dipping deposited samples, respectively. The long wavelength refractive index, average oscillator wavelength, and oscillator strength are also determined using the Sellmeier oscillator equation. The estimated third-order nonlinear optical susceptibility is found to be the order of 10−12 esu. The incident photon and charge carrier interaction in CH3NH3PbI3−xClx is studied from the dielectric response of the samples. The charge carrier excitation is found higher at lower wavelength and experienced bulk excitation in volume while surface excitation on the surface region. The optical conductivity of CH3NH3PbI3−xClx is notably high, which leads to an increase in carrier transfer through the extrinsic halide perovskite material expedient for higher conversion efficiency. The highest theoretical efficiency of CH3NH3PbI3−xClx is estimated to be 17.4%, which is in excellent agreement with the experimental report. From photosensitivity study, it is confirmed that CH3NH3PbI3−xClx films are highly photosensitive. All these results comprehend that CH3NH3PbI3−xClx is a potential candidate for photonic applications.

Hydrostatic pressure dependent structural, electronic, elastic and optical properties of Heusler compounds Cr2YAl (Y=Mn, Co) are investigated by the first-principles calculations. Present study shows good agreement between the calculated and experimental values of lattice parameters of these compounds. The gradual decrease of lattice parameter and unit cell volume with the increase of pressure eliminates the possibility of phase transition up to the considered pressure range 0–30 GPa. The absence of negative frequency in the phonon dispersion curves at various external pressures up to 30 GPa confirm the dynamical stability of these compounds. The values of Pugh's ratio, Poisson's ratio and Cauchy pressure indicate the ductility of Cr2CoAl while those criteria confirm the brittleness of Cr2MnAl. Pressure dependent behaviour of the elastic constants of these compounds shows the mechanical stability over the studied pressure range (0–30 GPa). Crystal stiffening of both the compounds is indicated by the increase of Debye temperature with increasing hydrostatic pressure. The pressure dependent band structure and density of states (DOS) calculations reveal the half- and the near half-metallic behaviour of Cr2MnAl and Cr2CoAl, respectively up to 20 GPa while those disappears at pressure around 30 GPa. The variations of optical constants with pressure is consistent with the results of the electronic structure calculations. High reflectivity (>45%) of both the compounds makes them attractive for optoelectronic device applications.

In 2021 May, the Dark Energy Spectroscopic Instrument (DESI) began a 5 yr survey of approximately 50 million total extragalactic and Galactic targets. The primary DESI dark-time targets are emission line galaxies, luminous red galaxies, and quasars. In bright time, DESI will focus on two surveys known as the Bright Galaxy Survey and the Milky Way Survey. DESI also observes a selection of “secondary” targets for bespoke science goals. This paper gives an overview of the publicly available pipeline ( desitarget ) used to process targets for DESI observations. Highlights include details of the different DESI survey targeting phases, the targeting ID ( TARGETID ) used to define unique targets, the bitmasks used to indicate a particular type of target, the data model and structure of DESI targeting files, and examples of how to access and use the desitarget code base. This paper will also describe “supporting” DESI target classes, such as standard stars, sky locations, and random catalogs that mimic the angular selection function of DESI targets. The DESI target-selection pipeline is complex and sizable; this paper attempts to summarize the most salient information required to understand and work with DESI targeting data.

Nano-fiber structure of ZnO and Ni doped ZnO (Ni:ZnO) transparent thin films have been deposited on glass substrate at 350 °C at an ambient atmosphere via spray pyrolysis technique. The structural, surface morphological and opto-electrical properties of ZnO and Ni doped ZnO thin films have been investigated. The XRD patterns show that the films are of polycrystalline in nature having preferential orientation (0 0 2) plane for ZnO changes to (1 0 1) by Ni doping in ZnO matrix. Optical study exhibits red shifting in band gap energy with Ni doping due to sp-d hybridization and display high absorption coefficient of the order of 107 m−1. The photoluminescence (PL) spectra indicate blue emissions in all samples. Electrical measurement confirms the resistivity of the film decreases remarkably with Ni doping and electrical transport is mainly thermally activated. From Hall Effect study, it is confirmed that all the samples are n-type having carrier concentration of the order of 1018 cm−3. Both mobility and carrier concentrations of the films became higher than ZnO sample with the increase of Ni concentration.