Sudhanshu Mallick

A simple route to making counter electrode for dye sensitized solar cells (DSSCs) using sucrose as carbon precursor.

Dye sensitized solar cells (DSSCs) have attracted much attention in recent years due to low cost fabrication as compared to silicon-based and thin film solar cells. Though, platinum is an excellent catalytic material for use in preparation of counter electrodes (CEs) for DSSCs it is expensive. Alternatives to replacement of platinum (Pt) that have been examined are carbon materials, conductive polymers and hybrids. In this work, counter electrode for DSSCs was fabricated using carbon material obtained from graphitization of sucrose at high temperature. A slurry of the carbon produced from sucrose graphitization was made with polyvinylpyrrolidone (PVP) as a surfactant and a coating was obtained by doctor blading the slurry over the FTO glass substrate. The current density (Jsc) and open circuit voltage (V(OC)) of fabricated cell (area 0.25 cm(2)) was 10.28 mAc m(-2) and 0.76 V respectively. The efficiency of the cell was 4.33% which was just slightly lower than that obtained for similar cells using platinum based counter electrode.

Effect of annealing atmosphere on quaternary chalcogenide-based counter electrodes in dye-sensitized solar cell performance: synthesis of Cu2FeSnS4 and Cu2CdSnS4 nanoparticles by thermal decomposition process

The synthesis of stoichiometrically controlled quaternary chalcogenide nanoparticles through a simple, eco-friendly process is still a great challenge. Herein, earth-abundant quaternary chalcogenide nanoparticles, Cu2FeSnS4 (CFTS) and Cu2CdSnS4 (CCdTS), were synthesized via the thermal decomposition of metal precursors. The prepared CFTS and CCdTS films were used as alternative counter electrodes (CEs) in dye-sensitized solar cells (DSSCs). The effects of the annealing atmosphere on morphology, elemental composition, electrical properties and electrochemical catalytic activity of the CFTS and CCdTS films were investigated. Energy dispersive spectroscopy, Hall measurements, cyclic voltammetry, and electrochemical impedance spectroscopy analysis demonstrate that the sulfurized CFTS and CCdTS-based CEs are more efficient for tri-iodide reduction as compared to the N2-annealed CFTS and CCdTS-based CEs. The photoconversion efficiencies (PCEs) of DSSCs fabricated with sulfurized, annealed in N2 atmosphere CFTS and CCdTS as CEs are found to 7.36 ± 0.00%, 5.78 ± 0.12% and 7.12 ± 0.08%, 5.30 ± 0.00% respectively, while the DSSCs fabricated with conventional Pt-based CEs show an efficiency of 8.15 ± 0.09%. These results indicate that the annealing atmosphere of the CEs has an impact on the DSSCs performance.

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 I-/I3- 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.

Combinatorial chemical bath deposition of CdS contacts for chalcogenide photovoltaics

Contact layers play an important role in thin film solar cells, but new material development and optimization of its thickness is usually a long and tedious process. A high-throughput experimental approach has been used to accelerate the rate of research in photovoltaic (PV) light absorbers and transparent conductive electrodes, however the combinatorial research on contact layers is less common. Here, we report on the chemical bath deposition (CBD) of CdS thin films by combinatorial dip coating technique and apply these contact layers to Cu(In,Ga)Se2 (CIGSe) and Cu2ZnSnSe4 (CZTSe) light absorbers in PV devices. Combinatorial thickness steps of CdS thin films were achieved by removal of the substrate from the chemical bath, at regular intervals of time, and in equal distance increments. The trends in the photoconversion efficiency and in the spectral response of the PV devices as a function of thickness of CdS contacts were explained with the help of optical and morphological characterization of the CdS thin films. The maximum PV efficiency achieved for the combinatorial dip-coating CBD was similar to that for the PV devices processed using conventional CBD. The results of this study lead to the conclusion that combinatorial dip-coating can be used to accelerate the optimization of PV device performance of CdS and other candidate contact layers for a wide range of emerging absorbers.

Electrochemical Synthesis of Novel Zn-Doped TiO2 Nanotube/ZnO Nanoflake Heterostructure with Enhanced DSSC Efficiency

The paper reports the fabrication of Zn-doped TiO2 nanotubes (Zn-TONT)/ZnO nanoflakes heterostructure for the first time, which shows improved performance as a photoanode in dye-sensitized solar cell (DSSC). The layered structure of this novel nanoporous structure has been analyzed unambiguously by Rutherford backscattering spectroscopy, scanning electron microscopy, and X-ray diffractometer. The cell using the heterostructure as photoanode manifests an enhancement of about an order in the magnitude of the short circuit current and a seven-fold increase in efficiency, over pure TiO2 photoanodes. Characterizations further reveal that the Zn-TONT is preferentially oriented in [001] direction and there is a Ti metal-depleted interface layer which leads to better band alignment in DSSC.Graphical Abstract

Low-temperature synthesis of Cu2CoSnS4 nanoparticles by thermal decomposition of metal precursors and the study of its structural, optical and electrical properties for photovoltaic applications

Copper-based chalcogenide quaternary semiconductors Cu2CoSnS4 (CCTS) have emerged as a promising material for thin film photovoltaic devices due to their opto-electrical properties and earth-abundant composition. The present study reports the synthesis of CCTS nanoparticles by a robust, solvent free, single step thermal decomposition process and their application in photovoltaics. Detailed studies of the effect of synthesis parameters (temperature, time) on crystallization, and the elemental composition of CCTS nanoparticles are reported. Physical, optical and electrical characterization of the as-synthesized nanoparticles and sulfurized films were carried out. The morphology and elemental composition of the synthesized nanoparticles are found to be similar to the nanoparticles synthesized by conventional solution processes. Electrical properties of the CCTS films are reported for the first time and are found to be carrier mobility (µ) = 36 cm2 V−1 s−1, carrier concentration (n) = 2 × 1016 cm−3, resistivity = 3 × 10−3 Ω m. Mott–Schottky analysis confirmed the p-type conductivity of the CCTS film. The films fabricated from the as-synthesized nanoparticles showed a photoresponse under illumination (100 mW cm−2). The optimum optical band gap (1.46 eV) and photoresponse of the CCTS film indicate that it can act as a promising cost-effective absorber layer for thin film solar cells.

Effect of Nanograss and Annealing Temperature on TiO2 Nanotubes Based Dye Sensitized Solar Cells

In TiO2 nanoparticle based dye sensitized solar cells (DSSC), the electron injected from the dye has to cross multiple interparticle boundaries in random directions before reaching the electrode. For application in DSSCs, the directional pathway for electron transport through the nanotubes is known to reduce the recombination rate. In the present study, titania nanotubes with nanograss layer have been fabricated by anodization of titanium foil in fluoride containing organic electrolyte. Dye sensitized solar cells with photoanode made of titania nanotubes covered with nanograsswas found to have a higher efficiency than ones made with only titania nanotubes of the same length.This can be attributed to enhanced dye adsorption on nanotubes with nanograss. The efficiency of DSSC using titania nanotubes is also affected by the annealing conditions such as duration, temperature.

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 (FAPbI3) and methylammonium lead bromide (MAPbBr3) mixed compositions of hybrid organic–inorganic perovskite type solar cells have shown the highest efficiency of 22.1%. For FAPbI3, two different polymorphs exist at room temperature: one is the hexagonal non-perovskite phase (δ-phase) and the other is the perovskite cubic phase (α-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 FAPbI3 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 δ-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 δ-phase growth. Experimentally, with the detailed solvent-induced time dependent crystallization study, we have proved the effective elimination of the δ-phase and the stability of the FA1−xMAxPbI3 perovskite phase.

RF Sputtered Iridium (Ir) Film as a Counter Electrode for Dye-Sensitized Solar Cells

Iridium (Ir) films were deposited on fluorine-doped tin oxide substrate by radio-frequency sputtering at room temperature and the as-deposited films were used as counter electrodes (CE) for dye-sensitized solar cells (DSSC). The photo conversion efficiency (PCE) of DSSC fabricated with Ir-based CE was 7.2%. Electrocatalytic activity and electrochemical data for Ir-based CE were compared with those for conventional Pt-based CE. The results were indicative of potential use of Ir as an alternative CE material for DSSC.

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.