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Vikram L. Dalal

Bio: Vikram L. Dalal is an academic researcher from Indian Institute of Technology Roorkee. The author has contributed to research in topics: Amorphous solid & Thin film. The author has an hindex of 27, co-authored 222 publications receiving 2791 citations. Previous affiliations of Vikram L. Dalal include University of Delaware & University of Western Ontario.


Papers
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TL;DR: In this paper, the authors measured dielectric constant, mid-gap defect density, Urbach energy of tail states in CH3NH3PbIxCl1−x perovskite solar cells.
Abstract: We report on measurement of dielectric constant, mid-gap defect density, Urbach energy of tail states in CH3NH3PbIxCl1−x perovskite solar cells. Midgap defect densities were estimated by measuring capacitance vs. frequency at different temperatures and show two peaks, one at 0.66 eV below the conduction band and one at 0.24 eV below the conduction band. The attempt to escape frequency is in the range of 2 × 1011/s. Quantum efficiency data indicate a bandgap of 1.58 eV. Urbach energies of valence and conduction band are estimated to be ∼16 and ∼18 meV. Measurement of saturation capacitance indicates that the relative dielectric constant is ∼18.

229 citations

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TL;DR: In this paper, a photonic-plasmonic nanostructure was proposed to enhance the absorption of long-wavelength photons in thin-film silicon solar cells, with the promise of exceeding the classical 4n2 limit for enhancement.
Abstract: We describe a photonic-plasmonic nanostructure, for significantly enhancing the absorption of long-wavelength photons in thin-film silicon solar cells, with the promise of exceeding the classical 4n2 limit for enhancement. We compare identical solar cells deposited on the photonic-plasmonic structure, randomly textured back reflectors and silver-coated flat reflectors. The state-of-the-art back reflectors, using annealed Ag or etched ZnO, had high diffuse and total reflectance. For nano-crystalline Si absorbers with comparable thickness, the highest absorption and photo-current of 21.5 mA/cm2 was obtained for photonic-plasmonic back-reflectors. The periodic photonic plasmonic structures scatter and reradiate light more effectively than a randomly roughened surface.

109 citations

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TL;DR: In this paper, the influence of film thickness and collision processes on the internal photoemission process in metal-semiconductor systems was studied using a simple, one-dimensional random walk model.
Abstract: We have studied the influence of film thickness and collision processes upon the internal photoemission process in metal‐semiconductor systems. A simple, one‐dimensional random walk model has been used. The analysis shows that significantly larger yields may be expected for film thicknesses of the order of or less than electron‐phonon mean free paths. The influence of energy dependent mean free paths has also been studied. The results are in qualitative agreement with the results of Fermi‐age theory, but are somewhat different quantitatively.

94 citations

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TL;DR: This structural study highlights the interaction and the role of catalytic residues of MEHP hydrolase involved in the biodegradation of PMEs to phthalate.

93 citations

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TL;DR: In this article, the authors fabricated metallic photonic crystal back-reflectors using photolithography and reactive-ion etching and deposited them in a-Si:H solar cells.
Abstract: Photonic crystal back-reflectors offer enhanced optical absorption in thin-film solar cells, without undesirable losses. We fabricated metallic photonic crystal back-reflectors using photolithography and reactive-ion etching and deposited a-Si:H solar cells. The photonic crystal has triangular lattice symmetry, a pitch of 760 nm, and was designed with rigorous simulations. Scanning electron microscopy demonstrates excellent long range periodicity and conformal a-Si:H growth. The average light absorption increases by 7%, relative to a flat reference device, with an enhancement factor approaching 6 at near-infrared wavelengths. The photonic crystal back reflector strongly diffracts light and increases optical path lengths of solar photons.

91 citations


Cited by
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Journal ArticleDOI
TL;DR: Recent advances in the understanding and application of plasmon-induced hot carrier generation are discussed and some of the exciting new directions for the field are highlighted.
Abstract: The discovery of the photoelectric effect by Heinrich Hertz in 1887 set the foundation for over 125 years of hot carrier science and technology. In the early 1900s it played a critical role in the development of quantum mechanics, but even today the unique properties of these energetic, hot carriers offer new and exciting opportunities for fundamental research and applications. Measurement of the kinetic energy and momentum of photoejected hot electrons can provide valuable information on the electronic structure of materials. The heat generated by hot carriers can be harvested to drive a wide range of physical and chemical processes. Their kinetic energy can be used to harvest solar energy or create sensitive photodetectors and spectrometers. Photoejected charges can also be used to electrically dope two-dimensional materials. Plasmon excitations in metallic nanostructures can be engineered to enhance and provide valuable control over the emission of hot carriers. This Review discusses recent advances in the understanding and application of plasmon-induced hot carrier generation and highlights some of the exciting new directions for the field.

2,511 citations

Journal ArticleDOI
24 Dec 2004-Science

1,949 citations

Journal ArticleDOI
TL;DR: In this paper, the authors summarize what is known and unknown about charge transport in HOIPs, with particular emphasis on their advantages as photovoltaic materials and highlight the fundamental questions that need to be addressed regarding the charge-transport properties of these materials.
Abstract: Solution-processed hybrid organic–inorganic perovskites (HOIPs) exhibit long electronic carrier diffusion lengths, high optical absorption coefficients and impressive photovoltaic device performance. Recent results allow us to compare and contrast HOIP charge-transport characteristics to those of III–V semiconductors — benchmarks of photovoltaic (and light-emitting and laser diode) performance. In this Review, we summarize what is known and unknown about charge transport in HOIPs, with particular emphasis on their advantages as photovoltaic materials. Experimental and theoretical findings are integrated into one narrative, in which we highlight the fundamental questions that need to be addressed regarding the charge-transport properties of these materials and suggest future research directions. The charge transport properties of hybrid organic—inorganic perovskites, which can explain their excellent photovoltaic performance, are reviewed through an integrated summary of experimental and theoretical findings. The potential origins of these properties are discussed and future research directions are indicated.

1,161 citations

Journal Article
TL;DR: The highly automated PHENIX AutoBuild wizard is described, which can be applied equally well to phases derived from isomorphous/anomalous and molecular-replacement methods.
Abstract: Iterative model-building, structure refinement, and density modification with the PHENIX AutoBuild Wizard Thomas C. Terwilliger a* , Ralf W. Grosse-Kunstleve b , Pavel V. Afonine b , Nigel W. Moriarty b , Peter Zwart b , Li-Wei Hung a , Randy J. Read c , Paul D. Adams b* a b Los Alamos National Laboratory, Mailstop M888, Los Alamos, NM 87545, USA Lawrence Berkeley National Laboratory, One Cyclotron Road, Bldg 64R0121, Berkeley, CA 94720, USA. c Department of Haematology, University of Cambridge, Cambridge CB2 0XY, UK. * Email: terwill@lanl.gov or PDAdams@lbl.gov Running title: The PHENIX AutoBuild Wizard Abstract The PHENIX AutoBuild Wizard is a highly automated tool for iterative model- building, structure refinement and density modification using RESOLVE or TEXTAL model- building, RESOLVE statistical density modification, and phenix.refine structure refinement. Recent advances in the AutoBuild Wizard and phenix.refine include automated detection and application of NCS from models as they are built, extensive model completion algorithms, and automated solvent molecule picking. Model completion algorithms in the AutoBuild Wizard include loop-building, crossovers between chains in different models of a structure, and side-chain optimization. The AutoBuild Wizard has been applied to a set of 48 structures at resolutions ranging from 1.1 A to 3.2 A, resulting in a mean R-factor of 0.24 and a mean free R factor of 0.29. The R-factor of the final model is dependent on the quality of the starting electron density, and relatively independent of resolution. Keywords: Model building; model completion; macromolecular models; Protein Data Bank; structure refinement; PHENIX Introduction Iterative model-building and refinement is a powerful approach to obtaining a complete and accurate macromolecular model. The approach consists of cycles of building an atomic model based on an electron density map for a macromolecular structure, refining the structure, using the refined structure as a basis for improving the map, and building a new model. This type of approach has been carried out in a semi-automated fashion for many years, with manual model-building iterating with automated refinement (Jensen, 1997). More recently, with the development first of ARP/wARP (Perrakis et al., 1999), and later other procedures including RESOLVE iterative model-building and refinement (Terwilliger,

1,161 citations