Tanaji Gujar

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A Solution Chemistry Approach for the Selective Formation of Ultralong Nanowire Bundles of Crystalline Cd(OH)2 on Substrates

Advanced Materials, 2008

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Characterization of pulsed laser deposited Cu2ZnSnS4 thin films for Solar cell

MRS Proceedings, 2012

ABSTRACTIn the present work we report the synthesis of Cu2ZnSnS4 (CZTS) films by pulsed laser dep... more ABSTRACTIn the present work we report the synthesis of Cu2ZnSnS4 (CZTS) films by pulsed laser deposition (PLD) and the effect of sulfur annealing on structure, composition, morphological and optical characterization of CZTS thin films. Raman spectra of the films exhibited the characteristics peaks of Kesterite structure. However, annealing caused to transfer the films from amorphous state into crystalline state. Scanning electron microscope (SEM) images revealed that as-deposited film exhibited a crack free, smooth, densely packed and homogeneous surface which was changed to rigid granular appearance after annealing. Energy dispersive X-ray spectroscopy (EDS) determined the compositions of the CZTS thin films which was near stoichiometry for the annealed samples. Ultraviolet–visible (UV–Vis) spectra showed the band gap of as-deposited film was 1.60 eV which was decreased to 1.40 eV after annealing.

Nanostructured Hybrid Metal Mesh as Transparent Conducting Electrodes: Selection Criteria Verification in Perovskite Solar Cells

Nanomaterials

Nanostructured metal mesh structures demonstrating excellent conductivity and high transparency a... more Nanostructured metal mesh structures demonstrating excellent conductivity and high transparency are one of the promising transparent conducting electrode (TCE) alternatives for indium tin oxide (ITO). Often, these metal nanostructures are to be employed as hybrids along with a conducting filler layer to collect charge carriers from the network voids and to minimize current and voltage losses. The influence of filler layers on dictating the extent of such ohmic loss is complex. Here, we used a general numerical model to correlate the sheet resistance of the filler, lateral charge transport distance in network voids, metal mesh line width and ohmic losses in optoelectronic devices. To verify this correlation, we prepared gold or copper network electrodes with different line widths and different filler layers, and applied them as TCEs in perovskite solar cells. We show that the photovoltaic parameters scale with the hybrid metal network TCE properties and an Au-network or Cu-network wi...

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Electrochemically Deposited Nanograin Ruthenium Oxide as a Pseudocapacitive Electrode

Crystalline structure of ruthenium oxide (RuO2) was electrochemically deposited onto tin doped in... more Crystalline structure of ruthenium oxide (RuO2) was electrochemically deposited onto tin doped indium oxide (ITO) electrode and used as electrodes to form a supercapacitor in a 0.5M H2SO4 electrolyte. The structural and surface morphological observations revealed the formation of nanograins of RuO2 of tetragonal crystal structure. For electrochemical supercapacitor application, electrochemically prepared crystalline RuO2 was found to be stable for large number of cycles with the specific capacitance 498 F/g at a scan rate of 5 mV/s. The specific capacitance is found to be dependent on the scan rate and the capacitance values varied inversely with scan rate.

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Double peak emission in lead halide perovskites by self-absorption

Journal of Materials Chemistry C

We demonstrate that the often observed double peak emission in lead halide perovskites is caused ... more

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Impact of excess PbI2 on the structure and the temperature dependent optical properties of methylammonium lead iodide perovskites

Journal of Materials Chemistry C

Excess PbI2 in MAPbI3 thin films has no direct impact on the electronic structure but changes the... more

Compact Layers of Hybrid Halide Perovskites Fabricated via the Aerosol Deposition Process—Uncoupling Material Synthesis and Layer Formation

Materials

We present the successful fabrication of CH 3 NH 3 PbI 3 perovskite layers by the aerosol deposit... more We present the successful fabrication of CH 3 NH 3 PbI 3 perovskite layers by the aerosol deposition method (ADM). The layers show high structural purity and compactness, thus making them suitable for application in perovskite-based optoelectronic devices. By using the aerosol deposition method we are able to decouple material synthesis from layer processing. Our results therefore allow for enhanced and easy control over the fabrication of perovskite-based devices, further paving the way for their commercialization.

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Highly Reproducible and Efficient Perovskite Solar Cells with Extraordinary Stability from Robust CH3NH3PbI3: Towards Large-Area Devices

Energy Technology

TiO2 Nanorods Decorated with Pd Nanoparticles for Enhanced Liquefied Petroleum Gas Sensing Performance

Analytical Chemistry

Development of highly sensitive and selective semiconductor-based metal oxide sensor devices to d... more Development of highly sensitive and selective semiconductor-based metal oxide sensor devices to detect toxic, explosive, flammable, and pollutant gases is still a challenging research topic. In the present work, we systematically enhanced the liquefied petroleum gas (LPG) sensing performance of chemical bath deposited TiO2 nanorods by decorating Pd nanoparticle catalyst. Surface morphology with elemental mapping, crystal structure, composition and oxidation states, and surface area measurements of pristine TiO2 and Pd:TiO2 nanorods was examined by high resolution transmission electron microscopy with energy-dispersive X-ray spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and nitrogen adsorption-desorption characterization techniques. LPG sensing performance of pristine TiO2 and Pd:TiO2 nanorods was investigated in different LPG concentration and operating temperature ranges. The LPG response of 21% for pristine TiO2 nanorods is enhanced to 49% after Pd catalyst decoration with reasonably fast response and recovery times. Further, the sensor exhibited long-term stability, which could be due to the strong metal support (Pd:TiO2) interaction and catalytic properties offered by the Pd nanoparticle catalyst. The work described herein demonstrates a general and scalable approach that provides a promising route for rational design of variety of sensor devices for LPG detection.

Perovskite Solar Cells: Capturing the Sun: A Review of the Challenges and Perspectives of Perovskite Solar Cells (Adv. Energy Mater. 16/2017)

Advanced Energy Materials

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Capturing the Sun: A Review of the Challenges and Perspectives of Perovskite Solar Cells

Advanced Energy Materials

He received his Ph.D. degree from Delft University of Technology in 2014, for his work on donor m... more He received his Ph.D. degree from Delft University of Technology in 2014, for his work on donor materials for organic solar cells, and was a visiting scholar at the University of Cambridge. His current research interests include the development of perovskite solar cells, with a focus on low-cost hole transporting materials, environmental impact, and stability of the perovskite. Sven Huettner currently works as an Assistant Professor (Juniorprofessor) at the University of Bayreuth. He received his diploma in physics from the University of Bayreuth in 2005, and worked on his Ph.D. degree in a joint collaboration with Prof. Ullrich Steiner (University of Cambridge) and Prof. Thelakkat (University of Bayreuth). From 2010-2013 he worked as a postdoc in the group of Prof. Sir Richard Friend (University of Cambridge) in the field of optoelectronics. His current research is concerned with investigating structure-function relations of novel organic and hybrid semiconductors toward applications in photovoltaics, transistors, and sensors.

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Characterization of perovskite solar cells: Towards a reliable measurement protocol

APL Materials, 2016

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Effect of Thermal and Structural Disorder on the Electronic Structure of Hybrid Perovskite Semiconductor CH3NH3PbI3

The journal of physical chemistry letters, Jan 20, 2016

In this paper, we investigate the temperature dependence of the optical properties of methylammon... more In this paper, we investigate the temperature dependence of the optical properties of methylammonium lead iodide (MAPbI3 = CH3NH3PbI3) from room temperature to 6K. In both, the tetragonal (T> 163K) and the orthorhombic (T<163K) phase of MAPbI3, the band gap (from both ab-sorption and photoluminescence (PL) measurements) de-creases with decrease in temperature - in contrast to what is normally seen for many inorganic semiconductors, like; Si, GaAs, GaN etc. We show that in the perovskites reported here, the temperature co-efficient of thermal expansion is large and accounts for the positive temperature coefficient of the band gap. A detailed analysis of the exciton linewidth allows to distinguish between static and dynamic disorder. The low energy tail of the exciton absorption is reminiscent of Urbach absorption. The Urbach energy is a measure of the disorder, which is modelled using thermal and static disorder for both the phases separately. The static disorder component, man...

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Reversible Laser Induced Amplified Spontaneous Emission from Coexisting Tetragonal and Orthorhombic Phases in Hybrid Lead Halide Perovskites

Advanced Optical Materials, 2016

This enabled the fabrication of perovskites solar cells that convinced the solar cell community w... more This enabled the fabrication of perovskites solar cells that convinced the solar cell community with high performances such as power conversion effi ciencies of over 20%, [ 4,5 ] while offering the possibility for low cost production, e.g., by solution-processing. [ 6 ] Meanwhile, further device applications for organic-inorganic mixed halide perovskites have been discovered. For example, in 2014, low threshold levels for amplifi ed spontaneous emission showed that mixed halide perovskites can also be used for the facile fabrication of lasers with high quality factors. [ 7-10 ] Furthermore, it is known that most halide perovskite materials can exist in different crystal structures, depending on environmental conditions such as temperature. [ 11-13 ] Here, we show that a coexistence of tetragonal and orthorhombic phases within apparently the same crystalline grain can be optically induced into the halide perovskite CH 3 NH 3 PbI 3 at low temperatures, leading to amplifi ed spontaneous emission (ASE) simultaneously at two distinct wavelengths. The ASE feature associated with the (high temperature) tetragonal phase can be reproducibly written, read-out, and erased at 5 K by choosing appropriate The photoluminescence in a lead halide perovskite is measured for different temperatures (5-300 K) and excitation fl uences (21-1615 µJ cm −2). It is found that amplifi ed spontaneous emission (ASE) is observed for an excitation density larger than about 1 × 10 18 cm −3 for both the tetragonal phase above 163 K and the orthorhombic phase below about 163 K. The fl uence that is required to obtain this excitation density depends on temperature and phase since the nonradiative decay of excitations is temperature activated with different activation energies of 85 20 ± and 24 5 meV ± for the tetragonal and orthorhombic phase, respectively. The ASE from the tetragonal phase-usually prevailing at temperatures above about 163 K-can also be observed at 5 K, in addition to the ASE from the orthorhombic phase, when the sample is previously exposed to a fl uence exceeding 630 µJ cm −2 at a photon energy of 3.68 eV. This additional ASE can be removed by mild heating to 35 K or optically, by exposing the sample by typically a few seconds with a fl uence around 630 µJ cm −2. The physical mechanism underlying this optically induced phase transition process is discussed. It is demonstrated that this phase change can, in principle, be used for an all-optical "write-read-erase" memory device.

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Nanomaterials for Energy Production and Storage

Journal of Nanotechnology, 2012

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Mn doped and undoped ZnO films: A comparative structural, optical and electrical properties study

... Phys. 85 (1999), p. 2595. OJPS full text | Full Text via CrossRef | View Record in Scopus | C... more

Ultralong Cadmium Chalcogenide Nanotubes from One-Dimensional Cadmium Hydroxide Nanowire Bundles by Soft Solution Chemistry

The Journal of Physical Chemistry C, 2009

... Ultralong Cadmium Chalcogenide Nanotubes from One-Dimensional Cadmium Hydroxide Nanowire Bund... more

Studies on growth of ZnO thin films by a novel chemical method

Solar Energy Materials and Solar Cells, 2007

... View Within Article. Table 1. Comparison of standard 'd' values with observed &#x27... more ... View Within Article. Table 1. Comparison of standard 'd' values with observed 'd' values of the ZnO thin films for P1, P2 and P3 samples Serial number, Standard 'd' (Å), P1 'd' (Å), P2 'd' (Å), P3 'd' (Å), (h k l). 1, 2.81, 2.81, 2.81, 2.81, 1 0 0. ... Energy Mater. Sol. Cells 88 (2005), p. 227. ...

Photoelectrochemical studies of chemically deposited nanocrystalline p-type HgS thin films

Solar Energy, 2007

ABSTRACT Nanocrystalline mercury sulfide (HgS) thin films were deposited by chemical bath deposit... more ABSTRACT Nanocrystalline mercury sulfide (HgS) thin films were deposited by chemical bath deposition (CBD) method onto the glass and fluorine doped tin oxide (FTO) coated glass substrate from an aqueous alkaline bath (pH∼8) at room temperature (300K). Mercuric acetate and thiourea were used as Hg2+ and S2− ion sources, respectively. The photoelectrochemical (PEC) studies of HgS films were carried out, and the nanocrystalline films were found to be photoactive in polyiodide solution. The PEC cell configuration was p-HgS/0.1M (KOH–KI–I2)/C. From the current–voltage (I–V) characteristics, it is concluded that the HgS films are of p-type electrical conductivity. The photovoltaic output characteristics were used to calculate the fill factor (ff) and solar conversion efficiency (η). The low value of η may be due to the high value of series resistance (Rs) and interface states in the cell, which are responsible for the recombination mechanism.

Room temperature liquefied petroleum gas (LPG) sensor based on p-polyaniline/n-TiO2 heterojunction

Sensors and Actuators B: Chemical, 2008

In the present work, we report on the performance of a room temperature (300 K) liquefied petrole... more In the present work, we report on the performance of a room temperature (300 K) liquefied petroleum gas (LPG) sensor based on a p-polyaniline/n-TiO 2 heterojunction. The heterojunction was fabricated using electrochemically deposited polyaniline on chemically deposited TiO 2 on a stainless steel substrate. Both the methods (chemical bath deposition and electrodeposition) are simple, inexpensive and suitable for large-scale production. TiO 2 and polyaniline films were characterized for their structural as well as surface morphologies and LPG response was studied. The XRD analysis showed formation of polycrystalline TiO 2 while polyaniline exhibited amorphous nature. Morphological analysis using scanning electron microscopy (SEM) of the junction cross-section revealed formation of a diffusion free interface. The heterojunction showed the maximum response of 63% upon exposure to 0.1 vol% LPG at room temperature.

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Tanaji Gujar

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