Experimental evaluation of room temperature crystallization and phase evolution of hybrid perovskite materials

To overcome the problems of thermal, moisture and photo-stability of existing methylammonium based perovskites, formamidinium-based compositions are introduced for photovoltaic application. Formamidinium lead iodide (FAPbI(3)) and methylammonium lead bromide (MAPbBr(3)) mixed compositions of hybrid organic-inorganic perovskite type solar cells have shown the highest efficiency of 22.1%. For FAPbI(3), two different polymorphs exist at room temperature: one is the hexagonal non-perovskite phase (delta-phase) and the other is the perovskite cubic phase (alpha-phase). The non-perovskite phase can be detrimental to the solar cell performance. To eradicate the undesired phase, a systematic evaluation of phase formation and crystallization is necessary. Here, we investigated the room temperature crystallization of the perovskite and non-perovskite phases of FAPbI(3) by solvent and antisolvent induced crystallization methods using a two-step sequential deposition method. For each phase, the volume fraction is estimated using the X-ray diffraction technique. At room temperature, the d-phase is found to grow as long one dimensional nanorods and its volume fraction increases with the dipping time. It is observed that the presence of an antisolvent has a moderate control on the d-phase growth. Experimentally, with the detailed solvent-induced time dependent crystallization study, we have proved the effective elimination of the d-phase and the stability of the FA(1)-(x)MA(x)PbI(3) perovskite phase

Liquid phase high shear exfoliated graphene nanoplatelets as counter electrode material for dye-sensitized solar cells

Graphene nanoplatelets (GNPs) are prepared from natural graphite by a simple and low-cost liquid phase high shear exfoliation method. The as-prepared GNPs are used as a counter electrode (CE) material for dye-sensitized solar cells (DSSCs). To confirm the Exfoliated GNPs, structural and morphological studies are carried out using X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and selected area electron diffraction (SAED) studies. The electrochemical behaviour of GNPs as a counter electrode material is evaluated and compared with standard Platinum (Pt) electrode using cyclic-voltammetry (CV) and electrochemical impedance spectroscopy (EIS). These studies indicated that electrocatalytic activity towards redox mediator exhibited by the GNPs based electrode is comparable to standard Pt counter electrodes. DSSCs are fabricated using the counter electrodes made of GNPs and the photo-conversion efficiency is found to be 6.23% under standard test conditions, which is comparable to Pt based DSSCs proving them as potential alternative materials for counter electrodes. (C) 2017 Published by Elsevier Inc

Anomalous magnetic behavior in nanocomposite materials of reduced graphene oxide-Ni/NiFe2O4

Magnetic Reduced Graphene Oxide-Nickel/NiFe2O4 (RGO-Ni/NF) nanocomposite has been synthesized by one pot solvothermal method. Respective phase formations and their purities in the composite are confirmed by High Resolution Transmission Electron Microscope and X Ray Diffraction, respectively. For the RGO-Ni/NF composite material finite-size effects lead to the anomalous magnetic behavior, which is corroborated in temperature and field dependent magnetization curves. Here, we are reporting the behavior of higher magnetization values for Zero Field Cooled condition to that of Field Cooled for the RGO-Ni/NF nanocomposite. Also, the observed negative and positive moments in Hysteresis loops at relatively smaller applied fields (100 Oe and 200 Oe) are explained on the basis of surface spin disorder. (C) 2014 AIP Publishing LLC

Improving the performance of carbon-based perovskite solar modules (70 cm2) by incorporating cesium halide in mesoporous TiO 2

We present the fabrication of highly efficient large-area carbon-based perovskite solar cells (C-PSCs) using CsX (X = Cl, Br, and I)-modified mesoporous (mp) TiO2 beads of 40 nm size as an electron transport material. Here, triple-layered scaffolds made of cesium halide-modified TiO2 exhibit efficient charge extraction as confirmed by enhanced photoluminescence quenching and inhibit the UV-activated degradation processes of perovskite, leading to an enhanced operational stability. Among the three cesium halide modifications, devices containing CsBr-modified TiO2 showed the highest short-circuit current density, yielding a photoconversion efficiency (PCE) of 12.59% of the device, with 0.7 cm(2) active area and 11.55% for a large-area module (70 cm(2)). These devices are stable in an ambient atmosphere (25 degrees C, 65-70% RH) over 2700 h as well as at a high temperature (85 degrees C) over 750 h with virtually no hysteresis