J. Renewable Sustainable Energy - Journal of Renewable and Sustainable Energy

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Synthesis and incorporation of high quality FeS₂ nanoparticles within poly(3-hexylthiophene):Phenyl-C60-butyric acid methyl ester to increase the photosensitivity of composite material

Animesh Layek, Somnath Middya, and Partha Pratim Ray

J. Renewable Sustainable Energy 5, 031601 (2013); http://dx.doi.org/10.1063/1.4807613 (9 pages)

Online Publication Date: 24 May 2013

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In this study, high quality environment friendly FeS₂ nanoparticle was synthesized in hydrothermal route with capping reagent. Band gap energy of FeS₂ has been modified and applied in polymer:inorganic nanocomposite. Pyrite structure of FeS₂ nanoparticle has been confirmed by different structural characterization techniques. Thermal stability has been studied by thermogravimetric analysis technique. Finally, FeS₂ has been introduced within a poly(3-hexylthiophene):Phenyl-C60-butyric acid methyl ester (P3HT:PCBM) matrix at different weight ratios to increase the photosensitivity of the nanocomposite. The composite film of P3HT:PCBM:FeS₂ with weight ratio 2:1:0.2 shows highest photosensitivity. Increased photosensitivity has been explained from photoluminescence data.

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78.55.-m	Photoluminescence, properties and materials
78.66.-w	Optical properties of specific thin films
64.75.Jk	Phase separation and segregation in nanoscale systems
61.46.Df	Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

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Improved photoelectrochemical performance of Cu(In,Ga)Se₂ thin films prepared by pulsed electrodeposition

Sreekanth Mandati, Bulusu V. Sarada, Suhash R. Dey, and Shrikant V. Joshi

J. Renewable Sustainable Energy 5, 031602 (2013); http://dx.doi.org/10.1063/1.4807615 (7 pages)

Online Publication Date: 24 May 2013

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Solar cells based on polycrystalline Cu(In,Ga)Se₂ absorber layers have yielded the highest conversion efficiency among all the thin-film technologies. CIGS thin-films possess large optical absorption coefficient (≈10⁵ cm⁻¹) and a suitable bandgap of ≈ 1.20 eV for an ideal stoichiometry of CuIn_0.7Ga_0.3Se₂. In the present study, Direct Current (DC) and Pulsed Current (PC) electrodeposition techniques are employed to obtain the near ideal stoichiometric CIGS thin-films on a Mo foil using a two electrode system at a constant potential. Deposited films are annealed at 550 °C under Ar atmosphere. Characterization of the annealed CIGS films is performed using SEM-energy dispersive X-ray spectroscopy, X-ray diffraction, Raman spectroscopy, and photoelectrochemistry to study the morphology, stoichiometry, phase constitution, and the photoelectrochemical response. PC deposition offered suitable manipulation of various parameters, which has helped in obtaining a better quality stoichiometric single phase chalcopyrite structured CIGS thin films with the elimination of unwanted secondary phases like Cu_2−xSe. An improved photoelectrochemical performance, characteristic of a p-type semiconductor, is observed for the PC deposited CIGS films.

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81.15.Pq	Electrodeposition, electroplating
82.45.Fk	Electrodes
82.50.-m	Photochemistry
61.72.Cc	Kinetics of defect formation and annealing
78.30.Hv	Other nonmetallic inorganics
78.66.Li	Other semiconductors

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Effect of embedding silica nanoparticles and voids in the performance of c-Si solar cells

Sonali Das, Avra Kundu, Hiranmay Saha, and Swapan K. Datta

J. Renewable Sustainable Energy 5, 031603 (2013); http://dx.doi.org/10.1063/1.4807618 (11 pages)

Online Publication Date: 24 May 2013

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The effect of embedding nanoentities (silica and voids) on the optical and electrical performance of Si solar cells has been investigated in an attempt to decouple the Anti-Reflection (AR) properties of the standard nitride coated Solar Cells (SCs) and the scattering properties of the nanoentities. The decoupling will ensure the use of the scattering properties of the nanoentities without disturbing the optimized reflection characteristics of a standard SC. Lumerical^® Finite Difference Time Domain Solutions software has been used to simulate the optical performance of solar cells after embedding nanoentities in the emitter region. Simulation results indicate that total decoupling of the AR properties and the scattering properties of the nanoentities is not obtained. Electrical performance evaluation of the system reveals a substantial relative improvement (1.7%) in the efficiency of thick (200 μm) SCs which further increases for thin (2 μm) film cells (23%) when 100 nm radius nanovoids having 30% area coverage are embedded at a depth of 200 nm from the silicon surface. The relative improvement is compromised if the changes in the material parameters due to embedding nanoentities are taken in to account.

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88.40.jj	Silicon solar cells
02.70.Bf	Finite-difference methods
88.40.hj	Efficiency and performance of solar cells

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Electrodeposited CuIn_1−xGa_xSe₂ thin films from non-aqueous medium for solar cell applications

N. B. Chaure

J. Renewable Sustainable Energy 5, 031604 (2013); http://dx.doi.org/10.1063/1.4808023 (7 pages)

Online Publication Date: 24 May 2013

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Polycrystalline thin films of group I-III-VI, especially copper indium diselenide and its alloys with gallium (CuIn_xGa_1−xSe₂, CIGS) have proven to be a suitable absorbers layer to obtain high-efficiency solar cells. We have deposited CuIn_xGa_1−xSe₂ (CIGS) thin films by cost effective electrochemical technique from non-aqueous bath onto fluorine doped tin oxide (FTO) coated glass substrates. The electrochemical parameters have been investigated by cyclic voltammetry in a non-aqueous solution of ethylene glycol, consisting precursors of Cu, In, Ga, and Se. The structural, morphological, compositional, and optoelectronic properties of CIGS thin films were studied. The prominent X-ray diffraction peak (112) is systematically shifted from 2θ = 26.60 to 27.26°, with increase in the contents of Ga in CIGS precursor layer. The atomic percentage of Ga in CIGS thin film was further confirmed by energy dispersive x-ray analysis technique. Preliminary solar cell devices (Glass/FTO/CdS/CIGS/Au) showed photoactive behavior with good diode characteristics in dark and under illumination conditions.

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88.40.H-	Solar cells (photovoltaics)
81.15.Pq	Electrodeposition, electroplating
82.80.Fk	Electrochemical methods

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Application of Si_xN_y:H_z (SiN) as index matching layer in a-Si:H thin film solar cells

Chandra Bhal Singh, Sekhar Bhattacharya, Vandana Singh, P. Balaji Bhargav, Surajit Sarkar, Venkateswarlu Bhavanasi, and Nafis Ahmad

J. Renewable Sustainable Energy 5, 031605 (2013); http://dx.doi.org/10.1063/1.4807609 (7 pages)

Online Publication Date: 28 May 2013

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The difference in refractive indices of glass substrate and transparent conducting oxide (TCO) electrode causes optical reflection in thin film solar cells, which results in lower absorption of light for devices. An anti-reflection layer between glass and TCO is required to reduce the loss of light due to optical reflection. Silicon nitride (Si_xN_y:H_z) films have shown antireflection property. The refractive index of Si_xN_y:H_z films can be engineered by changing the silicon or nitrogen content in the film. Here, we report the optimization of refractive index of Si_xN_y:H_z to achieve a value between refractive index of glass (1.5) and TCO film (2.0). Si_xN_y:H_z films have been deposited in a RF-plasma enhanced chemical vapour deposition system operating at a frequency of 13.56 MHz. The substrate temperature was fixed at 300 °C. Fourier transform infrared analysis has been used to determine the nature of Si-N, N-H, and Si-H bonding in the films. Refractive index of films has been measured using spectroscopic ellipsometer. The optical reflectance and transmission of Si_xN_y:H_z and Si_xN_y:H_z/TCO layers have been measured using UV/VIS spectrometer. The gas flow rate ratio of N₂/SiH₄ has been varied from 235 to 470. Decrease in transmittance of Si_xN_y:H_z/TCO layer is observed with increase in silicon concentration in the film. Refractive index of Si_xN_y:H_z also increased with an increase of the silicon content in the films. The reflectance of TCO films has been decreased from 15% to 8% when Si_xN_y:H_z film is incorporated between glass substrate and TCO film. An improvement of around 20% has been observed in current density of solar cells having Si_xN_y:H_z film as refractive index matching layer with refractive index 1.83. Thus, Si_xN_y:H_z film as refractive index matching layer can be used to improve the solar cells device efficiency.

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88.40.H-

Solar cells (photovoltaics)

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Influence of sulfurization temperature on physical properties of Cu₂ZnSnS₄ thin films

T. Narayana, Y. P. Venkata Subbaiah, P. Prathap, Y. B. K. Reddy, and K. T. Ramakrishna Reddy

J. Renewable Sustainable Energy 5, 031606 (2013); http://dx.doi.org/10.1063/1.4808019 (7 pages)

Online Publication Date: 30 May 2013

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Copper Zinc Tin Sulfide (Cu₂ZnSnS₄ or CZTS) is gaining much attention recently as a potential light absorber alternative to CuInGaSe₂ due to its suitable energy band gap ∼1.5 eV with p-type conductivity, high optical absorption coefficient of ∼10⁵ cm⁻¹. Moreover, all its constituents are abundant in the crust of the earth and environmentally harmless. In the present investigation, CZTS thin films were prepared using simple two step process of, sulfurization of sequentially sputtered stack, Glass/Zn/Sn/Cu (hereafter CTZ) metallic precursors on soda lime glass substrate held at temperature 200 °C. The sputter power was optimized individually for Zn, Sn, and Cu layers. The sputtered CTZ precursors were annealed at different temperatures in the range, 300–550 °C with an increment of 50 °C for 2 h in the ambience of vaporized elemental sulfur. The XRD pattern revealed that the films sulfurized in the temperature range 300–400 °C showed various spurious (binary and ternary) phases and the films sulfurized at 450 °C exhibited a clear phase corresponding to CZTS that becomes predominant at 500 °C. The optimized (500 °C) CZTS thin films showed kesterite structure with (112) preferred orientation. The sharp Raman shift centered at 336 cm⁻¹ confirms the single phase CZTS for the precursors sulfurized at 500 °C. From the transmittance measurements, the energy gap is found to be 1.62 eV for optimized CZTS films. The optical profilometer studies indicated an increase in the surface roughness with the sulfurization temperature. AFM measurements revealed compact morphology with pyramidal texture.

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68.55.ag	Semiconductors
61.43.Fs	Glasses
61.72.Cc	Kinetics of defect formation and annealing
81.05.Kf	Glasses (including metallic glasses)
81.15.Cd	Deposition by sputtering
68.55.A-	Nucleation and growth

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Anti-reflective nanocomposite based coating for crystalline silicon solar cells with noticeable significance

Utpal Gangopadhyay, Sukhendu Jana, Sayan Das, Prajit Ghosh, and Anup Mondal

J. Renewable Sustainable Energy 5, 031607 (2013); http://dx.doi.org/10.1063/1.4808154 (9 pages)

Online Publication Date: 4 June 2013

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Novel Diamond-like Nanocomposite (DLN) thin film as Anti-Reflective Nanocomposite Based (ARNAB) coating for crystalline silicon (c-Si) solar cell is the main objective of this paper. The DLN film was deposited by plasma assisted chemical vapour deposition (PACVD) method and characterized by Fourier transform infrared, field emission scanning electron microscope, and high resolution transmission emission microscope. Results show that c-Si₃N₄ and c-SiC nanoparticle (3–5 nm) were embedded in a-C:H matrix, and they were interpenetrated by Si-C bonding, i.e., typical DLN structure. The optical properties of the film were investigated by UV-VIS-near-infrared and photoluminescence spectroscopy. The performance of ARNAB coating was evaluated by measuring the reflectance, external quantum efficiency (EQE), and conversion efficiency. The solar weighted average reflection from textured c-Si was reduced to 2.25% in wavelength range 300 nm–1100 nm, and more than 90% EQE of the solar cell was achieved within the broad wavelength range 560 nm–870 nm. The result has been also compared with conventional silicon nitride anti-reflection coating (ARC). Finally, 0.8% absolute increased of efficiency was achieved with ARNAB layer in comparison with silicon nitride AR coating. The ARNAB thin film has a great potential to be used as ARC for silicon based solar cell.

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88.40.H-	Solar cells (photovoltaics)
81.07.-b	Nanoscale materials and structures: fabrication and characterization
81.15.Gh	Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
88.40.J-	Types of solar cells

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Microwave synthesis of copper indium gallium (di)selenide nanopowders for thin film solar applications

Raghunandan Seelaboyina, Manoj Kumar, Alekhya Venkata Madiraju, Kshitij Taneja, Anup Kumar Keshri, Sarang Mahajan, and Kulvir Singh

J. Renewable Sustainable Energy 5, 031608 (2013); http://dx.doi.org/10.1063/1.4808201 (7 pages)

Online Publication Date: 4 June 2013

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This work reports on the synthesis of nanopowder and nanoink of Copper-Indium-Gallium-(di)Selenide (CIGS) (CuIn_0.7Ga_0.3Se₂) of 20–80 nm with a band gap of 1.1 eV by a facile microwave technique. For CIGS synthesis, precursor mixtures consisting of metal acetylacetonates and selenium powder in oleylamine were heated in a microwave at 180–210 °C for 20–60 min. The resultant nanopowder was characterized and optimized for particle size by dynamic light scattering, phase by X-ray diffraction, morphology, and elemental distribution by scanning electron microscopy and band-gap by UV-Vis-near-infrared spectroscopy. CIGS ink, suitable for spin coating and ink-jet printing, was prepared and thin film was deposited and characterized.

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81.07.Wx	Nanopowders
81.15.Lm	Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
81.16.-c	Methods of micro- and nanofabrication and processing
84.40.-x	Radiowave and microwave (including millimeter wave) technology
88.40.jn	Thin film Cu-based I-III-VI2 solar cells
68.55.ag	Semiconductors

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Comparative studies of structural and electrical properties of co-doped ZnO thin films prepared by direct current sputtering as a front contact for copper indium gallium di-selenide solar cell

Chandan Ashis Gupta, S. Mangal, and U. P. Singh

J. Renewable Sustainable Energy 5, 031609 (2013); http://dx.doi.org/10.1063/1.4807617 (7 pages)

Online Publication Date: 5 June 2013

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Doped and co-doped ZnO thin films are currently under intense investigation and development for optoelectronic and solar cell applications. Here in this study Aluminum and Boron (ZAB), Gallium and Boron (ZGB), and Gallium and Aluminum (ZGA) co-doped ZnO thin films were deposited on glass substrate using DC magnetron sputtering at room temperature. A comparative study of the above co-doped ZnO thin films was done on the basis of its structural and electrical properties for solar cell application. All thin films have shown excellent optical properties with more than 80% transmission in the visible range of the light. From the X-ray diffraction patterns, it is found that the films were polycrystalline in nature and the ZAB thin film is more crystalline than the other co-doped ZnO thin films. The surface morphology showed different growth structure of the films. For ZAB and ZGA thin films, the rounded grains were observed and for ZGB thin film some rounded as well as corn type grains were observed. The electrical properties of all the thin films were measured using Hall measurement system at room temperature. For ZGB and ZGA thin films, the resistivity was obtained in the order of 10⁻³ ohm cm and for ZAB thin film the lowest resistivity of the order of 10⁻⁴ ohm cm was obtained which is ideal for transparent conducting oxide thin films to be used as window cum-front contact in multi-junction solar cell such as CIGS solar cell.

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73.61.Ga	II-VI semiconductors
78.66.Hf	II-VI semiconductors
81.15.Cd	Deposition by sputtering
68.55.ag	Semiconductors
88.40.H-	Solar cells (photovoltaics)

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Growth and characterization of co-evaporated Cu₂ZnSnS₄ thin films

U. Chalapathi, S. Uthanna, and V. Sundara Raja

J. Renewable Sustainable Energy 5, 031610 (2013); http://dx.doi.org/10.1063/1.4808256 (5 pages)

Online Publication Date: 5 June 2013

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Thin films of Cu₂ZnSnS₄ (CZTS), a potential absorber layer for thin film heterojunction solar cells, have been successfully grown on soda-lime glass substrates held at 450 ∘C using co-evaporation technique. Cu, Sn, ZnS, and S, kept in molybdenum boats, are used as the source materials. The as-deposited films are annealed at 550 ∘C for an hour under sulphur atmosphere to improve the crystallinity and sulphur content. Films exhibited kesterite structure with (112) preferred orientation. The lattice parameters are found to be a = 0.544 nm and c = 1.098 nm. The crystallite size increased from 90 nm to 105 nm on annealing at 550 ∘C. Raman spectroscopy analysis of annealed films confirmed the CZTS phase formation with Cu₂S as the secondary phase. The grain size is found to increase from 0.5 μm to 0.8 μm on annealing at 550 ∘C. The direct band gap of the annealed films is found to be 1.55 eV. The films are p-type in nature.

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81.05.Hd	Other semiconductors
68.55.ag	Semiconductors
81.15.Dj	E-beam and hot filament evaporation deposition
61.66.Fn	Inorganic compounds
61.72.Cc	Kinetics of defect formation and annealing
78.30.Hv	Other nonmetallic inorganics

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Synthesis of vertically grown N,N′-dioctyl-3,4,9,10-perylenedicarboximide nanostructure for photovoltaic application

S. Pradhan and A. Dhar

J. Renewable Sustainable Energy 5, 031611 (2013); http://dx.doi.org/10.1063/1.4809789 (7 pages)

Online Publication Date: 5 June 2013

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We report here the formation of vertical N,N′-dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C₈) nanostructure with simple chemical treatment over thermally evaporated thin film of PTCDI-C₈. Here, we have used PTCDI-C₈ nanostructures as an electron accepting material and a conjugated polymer as an electron donor material in the solar cell device. The study shows that the utilization of nanostructure over bilayer architecture gives better performance. The higher donor/acceptor effective interface and its effect on the device performance are realized with the nanostructured PTCDI-C₈ layer.

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81.16.-c	Methods of micro- and nanofabrication and processing
61.46.Df	Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
73.61.Ph	Polymers; organic compounds
68.35.bm	Polymers, organics
82.35.Cd	Conducting polymers
81.05.Lg	Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials

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Studies on antimony telluride thin films as buffer layer for solar cell applications

Shivaji M. Sonawane and N. B. Chaure

J. Renewable Sustainable Energy 5, 031612 (2013); http://dx.doi.org/10.1063/1.4808258 (6 pages)

Online Publication Date: 7 June 2013

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Antimony telluride (Sb₂Te₃) is binary p-type compound of narrow band gap (0.3 eV) semiconductor, which has application in solar cell to make low resistive ohmic contact. Sb₂Te₃ acts as a diffusion barrier and may improve the ohmic contact due to top doping on CdTe surface. We have synthesized antimony telluride thin films by electrodeposition technique and studied their various properties. Three-electrode system was employed for the electrodeposition of Sb₂Te₃ thin films on fluorine tin oxide coated glass substrates. Sb₂O₃ and TeO₂ were used as an ionic source for Sb and Te ions, whereas tartaric acid was used as complexing agent and also supportive electrolyte. The electrochemical parameters were optimized by slow scan cyclic voltammetry (CV) experiment. The effects of deposition potential on morphology, structure, and composition have been studied. Various properties of Sb₂Te₃ film were studied by X-ray diffraction, atomic force microscopy (AFM), and energy dispersive X-ray analysis. Prominent (015) peak of Sb₂Te₃ was attributed at 2θ = 28.36° for as-deposited and heat treated samples. After heat treatment, crystallinity of the film was improved. The electrical properties of as-deposited and annealed films were studied by two probe method. Growth potential dependent I-V characteristics of FTO/Sb₂Te₃/Au diode were studied and found to be Schottky barrier diode. Compact, uniform, and void free films surface morphology is observed by AFM. The effect of deposition potentials on morphology, structure, and composition of Sb₂Te₃ thin films were studied.

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88.40.jm	Thin film III-V and II-VI based solar cells
73.30.+y	Surface double layers, Schottky barriers, and work functions
73.40.Ns	Metal-nonmetal contacts
81.40.Gh	Other heat and thermomechanical treatments

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X-ray photoelectron spectroscopy and X-ray diffraction studies on tin sulfide films grown by sulfurization process

M. V. Reddy, P. Babu, K. T. Ramakrishna Reddy, and R. W. Miles

J. Renewable Sustainable Energy 5, 031613 (2013); http://dx.doi.org/10.1063/1.4809788 (6 pages)

Online Publication Date: 7 June 2013

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Tin sulfide (SnS) thin films were grown by single zone sulfurization process using sputtered tin layers. Metallic tin (Sn) layers were grown on molybdenum (Mo) coated soda-lime glass substrates by DC magnetron sputtering. The sputtered Sn layers along with sulfur flakes were kept in a graphite box and sulfurized using a closed single zone quartz tube furnace at different temperatures that vary in the range of 200–350 °C for a fixed sulfurization time of 2 h. The X-ray photoelectron spectroscopy studies on these layers revealed approximately stoichiometric ratio of Sn/S at a sulfurization temperature of 350 °C. The X-ray diffraction studies revealed the presence of secondary phases such as SnS₂ and Sn₂S₃ at lower sulfurization temperatures that got suppressed with the rise of temperature. All the layers showed the (111) plane as preferential orientation with orthorhombic structure and its intensity increased with the increase of sulfurization temperature. The evaluated crystallite size of the layers was found to increase with the increase of sulfurization temperature.

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81.05.Hd	Other semiconductors
68.55.ag	Semiconductors
68.55.A-	Nucleation and growth
81.15.Cd	Deposition by sputtering
81.05.uf	Graphite
61.66.Bi	Elemental solids
61.66.Dk	Alloys

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Controlling the absorption spectrum within a thin amorphous silicon layer by using the size dependent plasmonic behaviour of silver nanoparticles

Aparajita Mandal and Partha Chaudhuri

J. Renewable Sustainable Energy 5, 031614 (2013); http://dx.doi.org/10.1063/1.4809787 (7 pages)

Online Publication Date: 11 June 2013

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In this paper, we have used Finite Difference Time Domain method for numerically calculating the absorption spectra within a thin layer of hydrogenated amorphous silicon (a-Si:H) with the front surface regularly patterned with spherical Ag nano particles. We have considered a wide range of particle radius (40 nm ≤ R ≤ 200 nm) for including nano particles that have dipole dominated extinction spectra as well as the particles that can support multipole plasmon resonances. On performing the size variation analysis, constant surface coverage values (S) have been maintained so that the shading effect by the nano particles array will remain same for all particle sizes. We demonstrate that, for effective contribution to the absorption within the a-Si:H layer, there exists a clear distinction between the smaller size nanoparticles which support dipolar resonance and the larger size nano particles capable of producing higher order plasmon modes in terms of S values. The larger particles require much greater coverage than that of smaller particles for efficient plasmonic enhancement. These observations can have considerable importance in designing plasmonic solar cells or other optoelectronic devices that involve various sized Ag nano particles to enhance the optical absorption within an absorber layer.

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81.05.Cy	Elemental semiconductors
78.40.Fy	Semiconductors
81.05.Gc	Amorphous semiconductors
73.20.Mf	Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.68.+m	Optical properties of surfaces
61.46.Df	Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
78.20.Ci	Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

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Conventional and global maximum power point tracking techniques in photovoltaic applications: A review

A. Pallavee Bhatnagar and B. R. K. Nema

J. Renewable Sustainable Energy 5, 032701 (2013); http://dx.doi.org/10.1063/1.4803524 (22 pages)

Online Publication Date: 13 May 2013

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Maximum Power Point Tracking (MPPT) is a technique employed to extract maximum power available from a photovoltaic (PV) module under varying atmospheric conditions. It traces the PV operating voltage corresponding to the maximum power point (MPP) and operates the panel at MPP. However, if a PV array is partially shaded, the conventional MPPT techniques track local MPP and fail to track global MPP. Also, if modules with different optimal currents are connected in series—parallel local MPPs occur in the P-V curves and conventional MPPT techniques fail to search global maxima. A lot of literature is available on global MPPT techniques to increase overall system efficiency. The power conditioning unit should, therefore, be capable of searching global maximum power point also. This paper aims at presenting a number of conventional and global MPPT techniques; these methods are discussed in detail on the basis of certain performance parameters.

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84.30.Jc	Power electronics; power supply circuits
85.60.-q	Optoelectronic devices
88.40.H-	Solar cells (photovoltaics)

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Technical impacts of grid-connected photovoltaic systems on electrical networks—A review

M. S. ElNozahy and M. M. A. Salama

J. Renewable Sustainable Energy 5, 032702 (2013); http://dx.doi.org/10.1063/1.4808264 (11 pages)

Online Publication Date: 30 May 2013

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This paper addresses the potential impacts of grid-connected photovoltaic (PV) systems on electrical networks. The paper starts by emphasizing the increased importance of generating electricity from PV arrays. The growth in PV installed capacity worldwide is elaborated; futuristic expansion plans for several countries as well as existing PV projects worldwide are highlighted. The paper continues by evaluating the most important impacts of PV electricity on electrical networks. Finally, the authors summarize the literature's findings regarding the maximum allowable PV penetration that can be safely integrated into existing networks.

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84.70.+p	High-current and high-voltage technology: power systems; power transmission lines and cables
88.40.H-	Solar cells (photovoltaics)
88.80.Cd	Grid-connected distributed energy resources

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Present and prospective energy use potentials of selected agricultural wastes in Nigeria

C. N. Anyanwu, C. N. Ibeto, I. S. Eze, and S. L. Ezeoha

J. Renewable Sustainable Energy 5, 032703 (2013); http://dx.doi.org/10.1063/1.4808046 (13 pages)

Online Publication Date: 4 June 2013

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The present study reviews the potential energy applications of wastes derived from rice, cocoa, and oil palm to augment energy needs while helping to abate environmental pollution. It also highlights the potentials of animal dungs for energy production in Nigeria. The country currently produces about 2.7 × 10⁶ tons of rice annually, containing 0.540 × 10⁶ tons of rice husk and a similar quantity of straw, which can be used for energy production. About 6.22 × 10⁹ MJ of energy can be derived from the 266 000 tons (which could rise to 490 000 tons by 2015) of cocoa pods, which are currently produced and discarded annually. This could be utilized to generate process heat, either through thermal cycle or biochemical conversion. With respect to oil palm wastes, Nigeria generated about 0.344 × 10⁶ tonnes of empty fruit bunches, 0.246 × 10⁶ tonnes of palm shells, 0.633 × 10⁶ tonnes of palm oil mill effluent, and 0.382 × 10⁶ tonnes of mesocarp fibre in 2012, which are capable of producing substantial amounts of energy. Nigeria's livestock population is increasing at an annual rate of 3.2%, with current dung production of 407 × 10³ tons/day (cow), 28 × 10³ tons/day (pigs), 6.6 × 10³ tons/day (chicken broilers), etc., which is estimated to produce 6.8 × 10⁶ m³ of biogas daily. Electricity derivable from this quantity of biogas can provide lighting for 2.4 × 10⁶ rural households in Nigeria.

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88.20.dj	Agriculture/forestry residues
88.05.Qr	Energy use in agriculture

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Commentary: Materials for a sustainable energy future

Barbara Goss Levi

J. Renewable Sustainable Energy 5, 032801 (2013); http://dx.doi.org/10.1063/1.4811094 (2 pages)

Online Publication Date: 11 June 2013

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Abstract Unavailable

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01.10.Fv	Conferences, lectures, and institutes
88.05.Bc	Energy efficiency; definitions and standards

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Transport and interfacial transfer of electrons in dye-sensitized solar cells based on a TiO₂ nanoparticle/TiO₂ nanowire “double-layer” working electrode

Aixiang Wei, Zhipeng Zuo, Jun Liu, Kangbao Lin, and Yu Zhao

J. Renewable Sustainable Energy 5, 033101 (2013); http://dx.doi.org/10.1063/1.4803525 (10 pages)

Online Publication Date: 3 May 2013

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Dye-sensitized solar cells (DSSCs) with different thickness TiO₂ nanoparticle films and a “double-layer” working electrode of TiO₂ nanoparticle/TiO₂ nanowire are fabricated. The influence of the TiO₂ nanoparticle films thickness and of a light-scattering layer of TiO₂ nanowire on the photovoltaic performance of DSSCs are investigated. The transport and interfacial transfer of electrons in DSSCs are investigated using intensity modulated photocurrent spectroscopy (IMPS), intensity modulated photovoltage spectroscopy (IMVS), and electrochemical impedance spectroscopy (EIS) to determine the lifetime, diffusion coefficient, and diffusion length of the electrons. The results indicate that the optimum TiO₂ nanoparticle films' thickness for DSSCs is about 14 μm. The introduction of the light-scattering layer leads to an obvious enhancement of the power conversion efficiency. This can mainly be attributed to the superior light-scattering ability, fast electron transport, and long electron lifetime, resulting in a larger electron diffusion coefficient and a higher charge collection efficiency, which are confirmed by IMPS, IMVS, and EIS.

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88.40.J-	Types of solar cells
61.46.Df	Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
82.45.Fk	Electrodes
82.80.Fk	Electrochemical methods

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Model study of combined wind and solar electricity production in Hungary

Imre M. Jánosi

J. Renewable Sustainable Energy 5, 033102 (2013); http://dx.doi.org/10.1063/1.4803528 (9 pages)

Online Publication Date: 3 May 2013

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Since large-scale and cheap energy storage is an unsolved problem, the main difficulty of using wind and solar electricity is caused by their intermittent nature. It is a widespread belief that the combination of the two renewable technologies generally improves the reliability and supply quality of electricity generation. Indeed, there are some locations where wind speeds are definitely larger during the nights because of the increased stability of the atmospheric boundary layer. However, a proper decision making requires to study the supposed benefits at the very location of designed installations. Here, we report on a model study, where the whole area of Hungary is evenly covered by wind generators and solar photovoltaic units of various composition and total rated power. The combined model output is compared to the recorded electricity consumption in Hungary. Our results indicate that the integrated output of combined renewable production can be definitely lower than the output of “pure” (either solar or wind) resource network of the same rated power. The main reasons are the lack of daily cycle of wind strength and the strong annual seasonality of insolation in the Carpathian basin. Benefits of combined production show up at unrealistically high rated power values which is a consequence of limited capacity factors of both renewable sources around Hungary.

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88.05.-b	Energy analysis
88.40.-j	Solar energy
88.80.-q	Energy delivery and storage
88.50.J-	Wind farms
88.80.F-	Energy storage technologies

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A comprehensive view on performance, emission, and combustion characteristics of biodiesel-diesel blends at advanced injection timings

A. Murugesan, D. Subramaniam, A. Avinash, and N. Nedunchezhian

J. Renewable Sustainable Energy 5, 033103 (2013); http://dx.doi.org/10.1063/1.4803745 (10 pages)

Online Publication Date: 3 May 2013

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In this article, an endeavor has been made to assess the operating characteristics of a diesel engine fuelled with methyl esters of pungamia, ethyl esters of pungamia, and ethyl esters of neem, added to diesel by percentage volume ranging from B20 to B80. The test runs on diesel fuel in the first phase of work were carried out under standard injection timing of 23° before top dead center (BTDC), so as to establish baseline for other parameters. The similar test procedures were repeated with an advanced injection timings of 26° BTDC and 28° BTDC fuelled with diesel and biodiesel–diesel blends varying from B20 to B100. Experimental results proved that the 3° advancement of injection timing from the standard injection timing proved promising outcomes for biodiesel operated engine, whereas 5° BTDC crank angle degree produced a higher exhaust gas temperature and higher levels of NO_x formation.

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88.05.Np	Environmental aspects
89.20.Bb	Industrial and technological research and development
89.20.Kk	Engineering
88.20.jj	Combustion

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Optimization of biohydrogen production by Enterobacter species using artificial neural network and response surface methodology

P. Karthic, Shiny Joseph, Naveenji Arun, and S. Kumaravel

J. Renewable Sustainable Energy 5, 033104 (2013); http://dx.doi.org/10.1063/1.4803746 (12 pages)

Online Publication Date: 3 May 2013

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Optimization studies on fermentative hydrogen production were investigated using a facultative bacteria namely, Enterobacter species (MTCC 7104). The present study emphasizes the application of mathematical tools such as response surface methodology (RSM) and artificial neural network (ANN) to predict the maximum yield of hydrogen from the optimized carbon and nitrogen source. The key components such as glucose, initial pH, xylose, tryptone, yeast extract, sucrose, and peptone were screened using the Plackett-Burman design. Furthermore, rotatable central composite design and analysis of variance were adopted to investigate the interactive effect of the significant variables (xylose concentration, initial pH, and peptone concentration). Maximum experimental hydrogen yield of 1.94 mol H₂/mol xylose was achieved at the optimal points predicted by the RSM. Modeling ability of ANN and RSM has also been evaluated on predicting the maximum hydrogen yield with the estimated values of root mean square error (RMSE), multiple correlation coefficients (R²), and standard error of prediction (SEP). The estimated values of RMSE, R², and SEP for ANN model and RSM model confirm that fitness and prediction accuracy of ANN model were higher when compared to RSM model. Energy conversion efficiency and energy recovery analysis were performed for hydrogen production process using xylose as the source material.

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87.85.M-	Biotechnology
02.60.Pn	Numerical optimization
02.70.Rr	General statistical methods

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Solar cell parameters estimation from illuminated I-V characteristic using linear slope equations and Newton-Raphson technique

Shubham Raj, Ankit Kumar Sinha, and Ashish K. Panchal

J. Renewable Sustainable Energy 5, 033105 (2013); http://dx.doi.org/10.1063/1.4803748 (8 pages)

Online Publication Date: 3 May 2013

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To extract maximum output power from a solar cell, it is essential to know the solar cell parameters such as the photo-current (I_ph), the series resistance (R_se), the shunt resistance (R_sh), the reverse saturation current (I₀), and the diode ideality factor (n). This paper presents new and simple methods for estimating the cell parameters. First, R_se and R_sh are estimated from the intercepts of the linear slope equations dV/dI and dI/dV at the open circuit voltage (V_oc) and the short circuit current (I_sc) regions, respectively. The slopes of these equations also give I₀ and n, known as method-1. In method-2, using R_se and R_sh obtained by method-1, I₀ and n are estimated using Newton-Raphson technique. The methods presented here are applied to the illuminated I-V characteristics of silicon solar cells, an organic solar cell, and a dye sensitized solar cell previously reported in the literatures. The studies show that method-1 is more suitable for the solar cells with 70% or above fill factor whereas method-2 is suitable for all kinds of solar cells irrespective of fill factor.

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88.40.jr	Organic photovoltaics
02.60.-x	Numerical approximation and analysis

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The simultaneous effect of a fairing tower and increased blade flexibility on a downwind mounted rotor

M. Reiso and M. Muskulus

J. Renewable Sustainable Energy 5, 033106 (2013); http://dx.doi.org/10.1063/1.4803749 (11 pages)

Online Publication Date: 3 May 2013

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This is a parametric study on how blade and tower loads for a prototypical downwind offshore wind turbine are affected as the tower geometry and blade properties are changed. Downwind turbines have the potential to reduce the cost of energy, as blades can be more flexible and lighter, but the tower shadow induces additional structural vibrations. In order to reduce the latter, a fairing around the tower has been introduced. The length of the fairing is varied, adjusting the rotor overhang accordingly. Additionally, the blade weight and stiffness are adjusted. The blade and tower fatigue loads are, thereby, significantly decreased. In the first case, a maximum reduction of 8% and 28% (for the blade root bending and tower bottom moment, respectively) was achieved, compared to a downwind version of the National Renewable Energy Laboratory (NREL) 5 MW reference wind turbine on a monopile tower. Using softer and lighter blades resulted in loads even lower than for the conventional upwind rotor of the NREL turbine, up to 5% and 13% less for the blade and tower fatigue loads, respectively. The increased overhang increased the mean tower bending moments, suggesting that an optimal downwind turbine needs to be designed with a compromise between these fatigue and ultimate loads. The power production stayed approximately the same as that of a conventional wind turbine or was slightly higher.

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88.50.G-

Wind turbines

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Enhancement of efficiency of a conducting polymer P3HT:CdSe/ZnS quantum dots hybrid solar cell by adding single walled carbon nanotube for transporting photogenerated electrons

Shiv Kumar Dixit, Shikha Madan, Amandeep Kaur, Devinder Madhwal, Inderpreet Singh, P. K. Bhatnagar, P. C. Mathur, and C. S. Bhatia

J. Renewable Sustainable Energy 5, 033107 (2013); http://dx.doi.org/10.1063/1.4807475 (6 pages)

Online Publication Date: 21 May 2013

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Hybrid solar cells consisting of a composite of poly (3-hexylthiophene) (P3HT), single walled carbon nanotube (SWCNT), and cadmium selenide/zinc sulphide (CdSe/ZnS) coreshell quantum dots (QDs) have been fabricated in the present work. The bulk hetrojunction has been formed from the bilayer of P3HT:SWCNT composite and QDs using inter-diffusion process. Due to low percolation limit and high conductivity of SWCNT, the photo-generated electrons are collected at the electrode very fast (within few femto-seconds) enhancing the efficiency of the solar cell. The absorption measurements on the composite film show that the addition of SWCNT in the hybrid structure increases the absorption coefficient in the near infrared region and also makes the spectrum wider as compared to that of P3HT. The photoluminescence (PL) measurements show that the PL of hybrid P3HT, SWCNT, and QDs is quenched about ∼15 times as compared to that of P3HT film. This shows that a significant charge transfer of electrons occurs through SWCNT to the electrode. The morphology of P3HT:SWCNT:CdSe/ZnS was observed using atomic force microscopy. With this approach, we have been able to achieve power conversion efficiency of 5.4% using a standard solar simulator with an irradiance of 100 mW/cm².

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88.40.H-	Solar cells (photovoltaics)
81.05.Qk	Reinforced polymers and polymer-based composites
82.45.Fk	Electrodes
82.45.Wx	Polymers and organic materials in electrochemistry

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Volume 5, Issue 3 (partial)

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