International Journal of Photoenergy The latest articles from Hindawi Publishing Corporation © 2014 , Hindawi Publishing Corporation . All rights reserved. Optical and Structural Characterization of Nickel Coatings for Solar Collector Receivers Thu, 21 Aug 2014 00:00:00 +0000 The development of spectrally selective materials is gaining an increasing role in solar thermal technology. The ideal spectrally selective solar absorber requires high absorbance at the solar spectrum wavelengths and low emittance at the wavelengths of thermal spectrum. Selective coating represents a promising route to improve the receiver efficiency for parabolic trough collectors (PTCs). In this work, we describe an intermediate step in the fabrication of black-chrome based solar absorbers, namely, the fabrication and characterization of nickel coatings on stainless steel substrates. Microstructural characteristics of nickel surfaces are known to favorably affect further black chrome deposition. Moreover, the high reflectivity of nickel in the thermal infrared wavelength region can be advantageously exploited for reducing thermal emission losses. Thus, this report investigates structural features and optical properties of the nickel surfaces, correlating them to coating thickness and deposition process, in the perspective to assess optimal conditions for solar absorber applications. Stefano Pratesi, Elisa Sani, and Maurizio De Lucia Copyright © 2014 Stefano Pratesi et al. All rights reserved. A Hybrid MCDM Model for Improving GIS-Based Solar Farms Site Selection Wed, 20 Aug 2014 07:29:42 +0000 The purpose of this research is to establish a decision model for improving the performance of solar farms. To investigate the interdependent interrelationship and influential weights among criteria for solar farms site selection, a hybrid MCDM model including decision-making trial and evaluation laboratory (DEMATEL) and DEMATEL-based analytic network process (DANP) based on geographical information systems (GIS) is utilized. The empirical results display that there are interdependence and self-effect relationships among criteria via DEMATEL technique. According to the influential network relation map (INRM), the dimension that administrators of solar energy industry should improve first when enhancing the performance of solar farms is orography. In the ten criteria, solar radiation is the most important criterion impacting solar farms site selection, followed by average temperature and distance to villages. Chao-Rong Chen, Chi-Chen Huang, and Hung-Jia Tsuei Copyright © 2014 Chao-Rong Chen et al. All rights reserved. Innovative Solar Tracking Concept by Rotating Prism Array Wed, 20 Aug 2014 00:00:00 +0000 Solar energy has become one of the most promising renewable energies and is the most widely used nowadays. In order to achieve an optimum performance, both photovoltaic and solar thermal applications are required to track the position of the sun throughout the day and year in the most effective way possible to avoid a high negative impact on the system efficiency. The present paper attempts to describe a novel semipassive solar tracking concentrator (SPSTC) in which, in order to track the sun, two independent arrays of polymethyl methacrylate (PMMA) prisms are implemented to refract sunlight by rotating said prisms, thus being able to redirect solar radiation as desired. The first set is responsible for eliminating one of the directional components of the solar radiation; the task is achieved by rotating the prisms within the array at a specific angle. The second set deals with another of the sunlight’s directional components, transforming its direction into a completely perpendicular pattern to the array. Having downward vertical radiation makes it possible to implement a stationary Fresnel lens to concentrate the solar radiation for any application desired. The system is designed and validated using simulation software to prove the feasibility of the concept. Héctor García, Carlos Ramírez, and Noel León Copyright © 2014 Héctor García et al. All rights reserved. Investigation on Thermal Degradation Process of Polymer Solar Cells Based on Blend of PBDTTT-C and BM Tue, 19 Aug 2014 11:41:04 +0000 The effects of thermal treatment on the photovoltaic performance of conventional and inverted polymer solar cells (PSCs) based on the combination of poly[(4,8-bis-(2-ethylhexyloxy)-benzo[1,2-b;4,5-b′]dithiophene)-2,6-diyl-alt-(4-(2-ethylhexanoyl)-thie-no[3,4-b]thiophene))-2,6-diyl] (PBDTTT-C) and [6,6]-phenyl C70-butyric acid methyl ester (PC70BM) are investigated. The transient photoconductivity, the absorption spectra, and the transmission electron microscopy (TEM) images have been employed to study the thermal degradation of the inverted PSCs. The degradation is attributed to the inefficient charge generation and imbalance in charge-carrier transport, which is closely associated with the morphological evolution of the active layer with prolonged heating time. Yu Ning, Longfeng Lv, Yunzhang Lu, Aiwei Tang, Yufeng Hu, Zhidong Lou, Feng Teng, and Yanbing Hou Copyright © 2014 Yu Ning et al. All rights reserved. Cadmium Sulfide Nanoparticles Synthesized by Microwave Heating for Hybrid Solar Cell Applications Tue, 19 Aug 2014 08:27:30 +0000 Cadmium sulfide nanoparticles (CdS-n) are excellent electron acceptor for hybrid solar cell applications. However, the particle size and properties of the CdS-n products depend largely on the synthesis methodologies. In this work, CdS-n were synthetized by microwave heating using thioacetamide (TA) or thiourea (TU) as sulfur sources. The obtained CdS-n(TA) showed a random distribution of hexagonal particles and contained TA residues. The latter could originate the charge carrier recombination process and cause a low photovoltage (, 0.3 V) in the hybrid solar cells formed by the inorganic particles and poly(3-hexylthiophene) (P3HT). Under similar synthesis conditions, in contrast, CdS-n synthesized with TU consisted of spherical particles with similar size and contained carbonyl groups at their surface. CdS-n(TU) could be well dispersed in the nonpolar P3HT solution, leading to a of about 0.6–0.8 V in the resulting CdS-n(TU) : P3HT solar cells. The results of this work suggest that the reactant sources in microwave methods can affect the physicochemical properties of the obtained inorganic semiconductor nanoparticles, which finally influenced the photovoltaic performance of related hybrid solar cells. Claudia Martínez-Alonso, Carlos A. Rodríguez-Castañeda, Paola Moreno-Romero, C. Selene Coria-Monroy, and Hailin Hu Copyright © 2014 Claudia Martínez-Alonso et al. All rights reserved. Sensitization of Perovskite Strontium Stannate SrSnO3 towards Visible-Light Absorption by Doping Mon, 18 Aug 2014 11:19:33 +0000 Perovskite strontium stannate SrSnO3 is a promising photocatalyst. However, its band gap is too large for efficient solar energy conversion. In order to sensitize SrSnO3 toward visible-light activities, the effects of doping with various selected cations and anions are investigated by using hybrid density functional calculations. Results show that doping can result in dopant level to conduction band transitions which lie lower in energy compared to the original band gap transition. Therefore, it is expected that doping SrSnO3 can induce visible-light absorption. Hungru Chen and Naoto Umezawa Copyright © 2014 Hungru Chen and Naoto Umezawa. All rights reserved. Integrating Photovoltaic Systems in Power System: Power Quality Impacts and Optimal Planning Challenges Sun, 17 Aug 2014 12:49:01 +0000 This paper is an overview of some of the main issues in photovoltaic based distributed generation (PVDG). A discussion of the harmonic distortion produced by PVDG units is presented. The maximum permissible penetration level of PVDG in distribution system is also considered. The general procedures of optimal planning for PVDG placement and sizing are also explained in this paper. The result of this review shows that there are different challenges for integrating PVDG in the power systems. One of these challenges is integrated system reliability whereas the amount of power produced by renewable energy source is consistent. Thus, the high penetration of PVDG into grid can decrease the reliability of the power system network. On the other hand, power quality is considered one of the challenges of PVDG whereas the high penetration of PVDGs can lead to more harmonic propagation into the power system network. In addition to that, voltage fluctuation of the integrated PVDG and reverse power flow are two important challenges to this technology. Finally, protection of power system with integrated PVDG is one of the most critical challenges to this technology as the current protection schemes are designed for unidirectional not bidirectional power flow pattern. Aida Fazliana Abdul Kadir, Tamer Khatib, and Wilfried Elmenreich Copyright © 2014 Aida Fazliana Abdul Kadir et al. All rights reserved. SiO2 Antireflection Coatings Fabricated by Electron-Beam Evaporation for Black Monocrystalline Silicon Solar Cells Sun, 17 Aug 2014 00:00:00 +0000 In this work we prepared double-layer antireflection coatings (DARC) by using the SiO2/SiNx:H heterostructure design. SiO2 thin films were deposited by electron-beam evaporation on the conventional solar cell with SiNx:H single-layer antireflection coatings (SARC), while to avoid the coverage of SiO2 on the front side busbars, a steel mask was utilized as the shelter. The thickness of the SiNx:H as bottom layer was fixed at 80 nm, and the varied thicknesses of the SiO2 as top layer were 105 nm and 122 nm. The results show that the SiO2/SiNx:H DARC have a much lower reflectance and higher external quantum efficiency (EQE) in short wavelengths compared with the SiNx:H SARC. A higher energy conversion efficiency of 17.80% was obtained for solar cells with SiO2 (105 nm)/SiNx:H (80 nm) DARC, an absolute conversion efficiency increase of 0.32% compared with the conventional single SiNx:H-coated cells. Minghua Li, Hui Shen, Lin Zhuang, Daming Chen, and Xinghua Liang Copyright © 2014 Minghua Li et al. All rights reserved. Materials, Designs, Fabrications, and Applications of Organic Electronic Devices Thu, 14 Aug 2014 05:46:59 +0000 Jwo-Huei Jou, Ramunas Lygaitis, K. R. Justin Thomas, and Liang-Sheng Liao Copyright © 2014 Jwo-Huei Jou et al. All rights reserved. An Improved Method for Sizing Standalone Photovoltaic Systems Using Generalized Regression Neural Network Mon, 11 Aug 2014 08:08:54 +0000 In this research an improved approach for sizing standalone PV system (SAPV) is presented. This work is an improved work developed previously by the authors. The previous work is based on the analytical method which faced some concerns regarding the difficulty of finding the model’s coefficients. Therefore, the proposed approach in this research is based on a combination of an analytical method and a machine learning approach for a generalized artificial neural network (GRNN). The GRNN assists to predict the optimal size of a PV system using the geographical coordinates of the targeted site instead of using mathematical formulas. Employing the GRNN facilitates the use of a previously developed method by the authors and avoids some of its drawbacks. The approach has been tested using data from five Malaysian sites. According to the results, the proposed method can be efficiently used for SAPV sizing whereas the proposed GRNN based model predicts the sizing curves of the PV system accurately with a prediction error of 0.6%. Moreover, hourly meteorological and load demand data are used in this research in order to consider the uncertainty of the solar energy and the load demand. Tamer Khatib and Wilfried Elmenreich Copyright © 2014 Tamer Khatib and Wilfried Elmenreich. All rights reserved. Investigation of Thermal Instability of Additive-Based High-Efficiency Organic Photovoltaics Sun, 10 Aug 2014 12:57:39 +0000 Most photovoltaics operate at high temperature under sunlight. In this work, the thermal instability of diiodooctane-based high-efficiency bulk heterojunction (BHJ) organic photovoltaics (OPVs) is studied. The BHJ layers were heated to various temperatures to investigate the changes in their physical properties using atomic force microscopy phase images. The mobilities of the carriers were characterized at various temperatures using the space-charge-limited current method, and the carrier lifetime was calculated by applying impedance spectroscopy to the simulated equivalent circuit of the OPV devices. En-Ping Yao, Yi-Jhe Tsai, and Wei-Chou Hsu Copyright © 2014 En-Ping Yao et al. All rights reserved. Low Temperature (180°C) Growth of Smooth Surface Germanium Epilayers on Silicon Substrates Using Electron Cyclotron Resonance Chemical Vapor Deposition Sun, 10 Aug 2014 08:44:28 +0000 This paper describes a new method to grow thin germanium (Ge) epilayers (40 nm) on c-Si substrates at a low growth temperature of 180°C using electron cyclotron resonance chemical vapor deposition (ECR-CVD) process. The full width at half maximum (FWHM) of the Ge (004) in X-ray diffraction pattern and the compressive stain in a Ge epilayer of 683 arcsec and 0.12% can be achieved. Moreover, the Ge/Si interface is observed by transmission electron microscopy to demonstrate the epitaxial growth of Ge on Si and the surface roughness is 0.342 nm. The thin-thickness and smooth surface of Ge epilayer grown on Si in this study is suitable to be a virtual substrate for developing the low cost and high efficiency III-V/Si tandem solar cells in our opinion. Furthermore, the low temperature process can not only decrease costs but can also reduce the restriction of high temperature processes on device manufacturing. Teng-Hsiang Chang, Chiao Chang, Yen-Ho Chu, Chien-Chieh Lee, Jenq-Yang Chang, I-Chen Chen, and Tomi T. Li Copyright © 2014 Teng-Hsiang Chang et al. All rights reserved. Photophysical Properties of Pheophorbide-a Derivatives and Their Photodynamic Therapeutic Effects on a Tumor Cell Line In Vitro Sun, 10 Aug 2014 08:42:47 +0000 Pheophorbide-a derivatives have been reported to be potential photosensitizers for photodynamic therapy (PDT). In this study, photophysics of pheophorbide-a derivatives (PaDs) were investigated along with their photodynamic tumoricidal effect in vitro. PaDs were modified by changing the coil length and/or making the hydroxyl group (–OH) substitutions. Their photophysical properties were studied by steady-state and time-resolved spectroscopic methods. The photodynamic tumoricidal effect was evaluated in the mouse breast cancer cell line (EMT6). Lifetime and quantum yield of fluorescence and quantum yields of triplet state and singlet oxygen were studied to determine the dynamic energy flow. The coil length of the substituted alkyl group did not significantly affect the spectroscopic properties. However, the substitution with the hydroxyl group increased the quantum yields of the triplet state and the singlet oxygen due to the enhanced intersystem crossing. In order to check the application possibility as a photodynamic therapy agent, the PaDs with hydroxyl group were studied for the cellular affinity and the photodynamic tumoricidal effect of EMT6. The results showed that the cellular affinity and the photodynamic tumoricidal effect of PaDs with the hydroxyl group depended on the coil-length of the substituted alkyl group. Kang-Kyun Wang, Jing Li, Bong-Jin Kim, Jeong-Hyun Lee, Hee-Won Shin, Si-Hwan Ko, Won-Young Lee, Chang-Hee Lee, Seok Hoon Jung, and Yong-Rok Kim Copyright © 2014 Kang-Kyun Wang et al. All rights reserved. Estimation of Monthly Sunshine Duration in Turkey Using Artificial Neural Networks Sun, 10 Aug 2014 08:35:44 +0000 This paper introduces an artificial neural network (ANN) approach for estimating monthly mean daily values of global sunshine duration (SD) for Turkey. Three different ANN models, namely, GRNN, MLP, and RBF, were used in the estimation processes. A climatic variable (cloud cover) and two geographical variables (day length and month) were used as input parameters in order to obtain monthly mean SD as output. The datasets of 34 stations which spread across Turkey were split into two parts. First part covering 21 years (1980–2000) was used for training and second part covering last six years (2001–2006) was used for testing. Statistical indicators have shown that, GRNN and MLP models produced better results than the RBF model and can be used safely for the estimation of monthly mean SD. H. M. Kandirmaz, K. Kaba, and M. Avci Copyright © 2014 H. M. Kandirmaz et al. All rights reserved. Effect of Different Deposition Power of In2O3 Target on the Characteristics of IGZO Thin Films Using the Cosputtering Method Sun, 10 Aug 2014 06:25:10 +0000 The (In, Ga, Zn)Ox (IGZO) thin films were deposited on glass substrates using cosputtering method in radio frequency magnetron sputtering system. Zn2Ga2O5 (Ga2O3-2 ZnO, GZO) and In2O3 ceramics were used as targets and dual guns were used to deposit the IGZO thin films. Deposition power of GZO target was 80 W and deposition power of pure In2O3 target was changed from 70 W to 100 W, and the deposition time was 30 min. The effect of deposition power of In2O3 target on the crystalline, surface, electrical, and optical properties of the IGZO thin films was investigated at room temperature in a pure Ar atmosphere. The cosputtered IGZO thin films showed a very smooth and featureless surface and an amorphous structure regardless of the deposition power of In2O3 target due to the room temperature sputtering process. However, the cosputtered IGZO thin films exhibited transparent electrode properties because they had high transmittance ratio and low resistivity. The value variations in the optical band gap values of the IGZO thin film were evaluated from the plots of . We would also show that the deposition power of In2O3 target would have a large effect on mobility and value of the IGZO thin films. Shang-Chao Hung, Kin-Tak Lam, Cheng-Fu Yang, and Yu-Jhen Liou Copyright © 2014 Shang-Chao Hung et al. All rights reserved. Crystalline Silicon Solar Cells with Thin Silicon Passivation Film Deposited prior to Phosphorous Diffusion Sun, 10 Aug 2014 00:00:00 +0000 We demonstrate the performance improvement of p-type single-crystalline silicon (sc-Si) solar cells resulting from front surface passivation by a thin amorphous silicon (a-Si) film deposited prior to phosphorus diffusion. The conversion efficiency was improved for the sample with an a-Si film of ~5 nm thickness deposited on the front surface prior to high-temperature phosphorus diffusion, with respect to the samples with an a-Si film deposited on the front surface after phosphorus diffusion. The improvement in conversion efficiency is 0.4% absolute with respect to a-Si film passivated cells, that is, the cells with an a-Si film deposited on the front surface after phosphorus diffusion. The new technique provided a 0.5% improvement in conversion efficiency compared to the cells without a-Si passivation. Such performance improvements result from reduced surface recombination as well as lowered contact resistance, the latter of which induces a high fill factor of the solar cell. Ching-Tao Li, Fangchi Hsieh, Shi Yan, Cuifeng Wan, Yakun Liu, Jing Chen, and Likarn Wang Copyright © 2014 Ching-Tao Li et al. All rights reserved. Significant Inhibition of Tumor Growth following Single Dose Nanoparticle-Enhanced Photodynamic Therapy Thu, 07 Aug 2014 10:54:18 +0000 Photodynamic therapy (PDT) for cancer treatment involves the pathology’s uptake of photosensitizers, which produce cytotoxic reactive oxygen species by photoirradiation. The use of nanoparticles as carriers of photosensitizers is one promising approach to this endeavor, owing to their small size, unique physicochemical properties, and easy/diverse functionalization. In the current work, we report on the in vivo assessment of PDT efficacy of these nanoconstructs in a murine model of human breast cancer, following a single (one-shot) nanoparticle dose and photoirradiation. Palladium-porphyrin (PdTPP) was administered intratumorally via injection of aqueous suspensions of either free PdTPP or MSN-conjugated PdTPP (MSN-PdTPP) at a dose of 50 μg. Mice were then exposed to a single photoirradiation session with total energy of 80 J. One month after one-shot PDT treatment, significantly greater reductions in tumor growth were observed in MSN-Pd treated animals than in PdTPP cohorts. Electron microscopy of tumor specimens harvested at various timepoints revealed excellent MSN-PdTPP uptake by cancer cells while immunohistologic analysis demonstrated marked increases in apoptotic response of MSN-PdTPP treated animals relative to PdTPP controls. Taken together, these findings suggest that considerable improvements in PDT efficacy can readily be achieved via the use of nanoparticle-based photosensitizers. Shih-Hsun Cheng, Chia-Hui Chu, Nai-Tzu Chen, Jeffrey S. Souris, Chin-Tu Chen, and Leu-Wei Lo Copyright © 2014 Shih-Hsun Cheng et al. All rights reserved. Enhanced Efficiencies for High-Concentration, Multijunction PV Systems by Optimizing Grid Spacing under Nonuniform Illumination Thu, 07 Aug 2014 09:34:25 +0000 The design of a triple junction solar cell’s front contact grid can significantly affect cell conversion efficiency under high concentration. We consider one aspect of grid design, choosing a linear grid within a distributed resistance cell model to optimize finger spacings at concentrations between 500 and 2500 suns under uniform and nonuniform illumination. Optimization for maximum efficiency under Gaussian irradiance profiles is done by SPICE analysis. Relative to the optimized uniform illumination designs, we find enhancements of 0.5% to 2% in absolute efficiencies for uniform spacing. Efficiency enhancement with nonuniform spacing under nonuniform illumination is also evaluated. Our model suggests that, at lower concentrations (<1000 suns), the penalty for using uniformly spaced fingers instead of nonuniformly spaced fingers is <0.1%. However, at a concentration of 2500 suns the penalty increases to 0.3%. Thus, relative to a uniform irradiance optimization, an absolute efficiency increase of 2.3% can be attained for an optimized nonuniform spacing given the Gaussian irradiance profile under consideration. Pratibha Sharma, Alex W. Walker, Jeffrey F. Wheeldon, Karin Hinzer, and Henry Schriemer Copyright © 2014 Pratibha Sharma et al. All rights reserved. Seismic and Power Generation Performance of U-Shaped Steel Connected PV-Shear Wall under Lateral Cyclic Loading Wed, 06 Aug 2014 00:00:00 +0000 BIPV is now widely used in office and residential buildings, but its seismic performance still remained vague especially when the photovoltaic (PV) modules are installed on high-rise building facades. A new form of reinforced concrete shear wall integrated with photovoltaic module is proposed in this paper, aiming to apply PV module to the facades of high-rise buildings. In this new form, the PV module is integrated with the reinforced concrete wall by U-shaped steel connectors through embedded steel plates. The lateral cyclic loading test is executed to investigate the seismic behavior and the electric and thermal performance with different drift angles. The seismic behavior, including failure pattern, lateral force-top displacement relationship, and deformation capacity, was investigated. The power generation and temperature variation on the back of the PV module and both sides of the shear wall were also tested. Two main results are demonstrated through the experiment: (1) the U-shaped steel connectors provide enough deformation capacity for the compatibility of the PV module to the shear wall during the whole cyclic test; (2) the electricity generation capacity is effective and stable during this seismic simulation test. Hongmei Zhang, Jinzhi Dong, Yuanfeng Duan, Xilin Lu, and Jinqing Peng Copyright © 2014 Hongmei Zhang et al. All rights reserved. One-Dimensional Nanostructured TiO2 for Photocatalytic Degradation of Organic Pollutants in Wastewater Tue, 05 Aug 2014 08:26:51 +0000 The present paper reviews the progress in the synthesis of one-dimensional (1D) TiO2 nanostructures and their environmental applications in the removal of organic pollutants. According to the shape, 1D TiO2 nanostructures can be divided into nanorods, nanotubes, nanowires/nanofibers, and nanobelts. Each of them can be synthesized via different technologies, such as sol-gel template method, chemical vapor deposition, and hydrothermal method. These methods are discussed in this paper, and the recent development of the synthesis technologies is also presented. Furthermore, the organic pollutants, degradation using the synthesized 1D TiO2 nanostructures is studied as an important application of photocatalytic oxidation (PCO). The 1D nanostructured TiO2 exhibited excellent photocatalytic activity in a PCO process, and the mechanism of photocatalytic degradation of organic pollutants is also discussed. Moreover, the modification of 1D TiO2 nanostructures using metal ions, metal oxide, or inorganic element can further enhance the photocatalytic activity of the photocatalyst. This phenomenon can be explained by the suppression of e−-h+ pairs recombination rate, increased specific surface area, and reduction of band gap. In addition, 1D nanostructured TiO2 can be further constructed as a film or membrane, which may extend its practical applications. Ting Feng, Gen Sheng Feng, Lei Yan, and Jia Hong Pan Copyright © 2014 Ting Feng et al. All rights reserved. A Facile and Waste-Free Strategy to Fabricate Pt-C/TiO2 Microspheres: Enhanced Photocatalytic Performance for Hydrogen Evolution Tue, 05 Aug 2014 07:18:14 +0000 A facile and waste-free flame thermal synthesis method was developed for preparing Pt modified C/TiO2 microspheres (Pt-C/TiO2). The photocatalysts were characterized with X-ray diffraction, field emission scanning electron microscopy, transmission electron microscope, ultraviolet-visible (UV-vis) diffuse reflectance spectra, X-ray photoelectron spectroscopy, and thermogravimetry analysis. The photocatalytic activity was evaluated by hydrogen evolution from water splitting under UV-vis light illumination. Benefitting from the electron-hole separation behavior and reduced overpotential of H+/H2, remarkably enhanced hydrogen production was demonstrated and the photocatalytic hydrogen generation from 0.4 wt% Pt-C/TiO2 increased by 22 times. This study also demonstrates that the novel and facile method is highly attractive, due to its easy operation, requiring no post treatment and energy-saving features. Hui Li, Xiaoyan Zhang, and Xiaoli Cui Copyright © 2014 Hui Li et al. All rights reserved. In-Line Sputtered Gallium and Aluminum Codoped Zinc Oxide Films for Organic Solar Cells Tue, 05 Aug 2014 06:03:03 +0000 Gallium and aluminum codoped zinc oxide (GAZO) films were deposited at different temperatures by in-line sputtering. Aluminum is thermally unstable compared to other elements in GAZO films. The grains of GAZO films increase with deposition temperature. Coalescence between grains was observed for GAZO films deposited at 250°C. The deposition temperature exhibits positive influence on crystallinity, and electrical and optical properties of GAZO films. The carrier concentration and mobility of GAZO films increase, while the electrical resistivity of GAZO films decreases with deposition temperature. The average optical transmittance of GAZO films rises with deposition temperature. In-line sputtering demonstrates a potential method with simplicity, mass production, and large-area deposition to produce GAZO films with good electrical and optical quality. The electrical resistivity of 4.3 10−4 Ω cm and the average optical transmittance in the visible range from 400 to 800 nm of 92% can be obtained for GAZO films deposited at 250°C. The hybrid organic solar cells (OSC) were fabricated on GAZO-coated glass substrates. Blended poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) were the photoactive materials in OSC. The power conversion efficiency of OSC is 0.65% for the OSC with the 250°C deposited GAZO electrode. Shang-Chou Chang Copyright © 2014 Shang-Chou Chang. All rights reserved. Fabrication of Hybrid Organic Photovoltaic Devices Using Electrostatic Spray Method Mon, 04 Aug 2014 05:34:17 +0000 Hybrid organic photovoltaic devices (OPVDs) are fabricated using the electrostatic spray (e-spray) method and their optical and electrical properties are investigated. E-spray is used to deposit a hybrid film (P3HT: PCBM/nanodiamond) with morphology and optical characteristics onto OPVDs. The root-mean-square roughness and optical absorption increase with increasing nanodiamond content. The performance of e-spray is comparable to that of the spin-coating method under uniform conditions. The device takes advantage of the high current density, power conversion efficiency, and low cost. Nanodiamond improves the short-circuit current density and power conversion efficiency. The best performance was obtained with 1.5 wt% nanodiamond content, with a current density of 7.28 mA/cm2 and a power conversion efficiency of 2.25%. Zhe-Wei Chiu, Yu-Jen Hsiao, Te-Hua Fang, and Liang-Wen Ji Copyright © 2014 Zhe-Wei Chiu et al. All rights reserved. Competing Deactivation Channels for Excited π-Stacked Cytosines Sun, 03 Aug 2014 11:50:34 +0000 The deactivation of π-stacked cytosine molecules following excitation by ultrashort laser pulses was studied using semiclassical dynamics simulations. Another deactivation channel was found to compete with a previously reported path that led to dimerization. For both pathways, the initial excited state was found to form a charge-separated neutral exciton state, which forms an excimer state by charge transfer. When the interbase distance becomes less than 3 Å, charge recombination occurs due to strong intermolecular interaction, ultimately leading to an avoided crossing. Results indicate that the C2–N1–C6–C5 and ––– dihedral angles play a significant role in the vibronic coupling between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). Vibrational energy distribution determines the fate of the excimer at the avoided crossing. Higher-amplitude vibration of C5 or C6 atoms leads to a nonadiabatic transition to the electronic ground state (a photophysical pathway); otherwise, a chemical reaction leading to the formation of cyclobutane type dimer occurs as found in earlier studies. The S1 and S0 potential energy surfaces calculated at TD-DFT level and the simulated trajectories were found to be consistent with CASPT2 results. Shuai Yuan, Huiling Hong, Gang Wang, Wenying Zhang, Yusheng Dou, and Glenn V. Lo Copyright © 2014 Shuai Yuan et al. All rights reserved. Optical, Electrical and Photocatalytic Properties of the Ternary Semiconductors , and Sun, 03 Aug 2014 07:44:08 +0000 The effects of vacuum annealing at different temperatures on the optical, electrical and photocatalytic properties of polycrystalline and amorphous thin films of the ternary semiconductor alloys , and were investigated in stacks of binary semiconductors obtained by chemical bath deposition. The electrical properties were measured at room temperature using a four-contact probe in the Van der Pauw configuration. The energy band gap of the films varied from 2.30 to 2.85 eV. The photocatalytic activity of the semiconductor thin films was evaluated by the degradation of an aqueous methylene blue solution. The thin film of annealed under vacuum at 300°C exhibited the highest photocatalytic activity. Sandra Andrea Mayén-Hernández, David Santos-Cruz, Francisco de Moure-Flores, Sergio Alfonso Pérez-García, Liliana Licea-Jiménez, Ma. Concepción Arenas-Arrocena, José de Jesús Coronel-Hernández, and José Santos-Cruz Copyright © 2014 Sandra Andrea Mayén-Hernández et al. All rights reserved. Theoretical Study on Electronic Structure and Optical Performance of Nickel and Nitrogen Codoped Rutile Titanium Dioxide Thu, 24 Jul 2014 12:32:20 +0000 The nickel doped, nitrogen doped and nickel + nitrogen codoped rutile titanium dioxide have been investigated by ab initio calculations based on density functional theory. The electronic structure and optical performance of different ions doping models are researched through the obtained results, which reflects that the band gap of nickel and nitrogen codoped system declines apparently; the decrease of electron-hole pairs separation and charge carriers recombination rate becomes more desirable. Moreover, the optical absorption curves of nitrogen and nickel codoped rutile titanium dioxide demonstrate the higher photoresponse for visible-light than that of nickel or nitrogen single doped. The above results could provide theoretical basis for further developing of titanium dioxide photocatalyst and related experimental studies. Fei Wang, Lei Feng, Dongmei Zhang, Qingguo Tang, Jinsheng Liang, and Dan Feng Copyright © 2014 Fei Wang et al. All rights reserved. A Facile Synthesis of Graphene-WO3 Nanowire Clusters with High Photocatalytic Activity for O2 Evolution Thu, 24 Jul 2014 08:55:40 +0000 In the present work, graphene-WO3 nanowire clusters were synthesized via a facile hydrothermal method. The obtained graphene-WO3 nanowire clusters were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, and ultraviolet-visible diffuse reflectance spectroscopy (DRS) techniques. The photocatalytic oxygen (O2) evolution properties of the as-synthesized samples were investigated by measuring the amount of evolved O2 from water splitting. The graphene-WO3 nanowire clusters exhibited enhanced performance compared to pure WO3 nanowire clusters for O2 evolution. The amount of evolved O2 from water splitting after 8 h for the graphene-WO3 nanowire clusters is ca. 0.345 mmol/L, which is more than 1.9 times as much as that of the pure WO3 nanowire clusters (ca. 0.175 mmol/L). The high photocatalytic activity of the graphene-WO3 nanowire clusters was attributed to a high charge transfer rate in the presence of graphene. M.-J. Zhou, N. Zhang, and Z. H. Hou Copyright © 2014 M.-J. Zhou et al. All rights reserved. A Newton-Based Extremum Seeking MPPT Method for Photovoltaic Systems with Stochastic Perturbations Thu, 24 Jul 2014 00:00:00 +0000 Microcontroller based maximum power point tracking (MPPT) has been the most popular MPPT approach in photovoltaic systems due to its high flexibility and efficiency in different photovoltaic systems. It is well known that PV systems typically operate under a range of uncertain environmental parameters and disturbances, which implies that MPPT controllers generally suffer from some unknown stochastic perturbations. To address this issue, a novel Newton-based stochastic extremum seeking MPPT method is proposed. Treating stochastic perturbations as excitation signals, the proposed MPPT controller has a good tolerance of stochastic perturbations in nature. Different from conventional gradient-based extremum seeking MPPT algorithm, the convergence rate of the proposed controller can be totally user-assignable rather than determined by unknown power map. The stability and convergence of the proposed controller are rigorously proved. We further discuss the effects of partial shading and PV module ageing on the proposed controller. Numerical simulations and experiments are conducted to show the effectiveness of the proposed MPPT algorithm. Heng Li, Jun Peng, Weirong Liu, Zhiwu Huang, and Kuo-Chi Lin Copyright © 2014 Heng Li et al. All rights reserved. A Communication Based Islanding Detection Method for Photovoltaic Distributed Generation Systems Wed, 23 Jul 2014 07:25:06 +0000 PV based distributed generation (DG) systems must have some electrical connection standards while they connected to an electrical grid. One of these electrical conditions and the most important one is unplanned islanding condition. Islanding is a very dangerous condition because it could damage the PV system and related electrical systems and also working people have been at risk in islanding condition. In this application study, a new communication based islanding detection method was introduced for grid tied PV systems. A real time controller was developed with Labview for detecting islanding condition. Developed method is a hybrid method which uses the effective ways of communication based and passive methods. The results obtained from the proposed real time islanding detection method show that proposed method is reliable, robust, and independent from load and inverter. Nondetection zone (NDZ) is almost zero and islanding detection time is approximately 1-2 cycles indicated in experimental results so this time has a significant short response time according to IEEE 929-2000 standard. The proposed method is effective and presents a realistic solution to islanding so it could be implemented easily to grid tied PV systems and could be used in real system applications. Gökay Bayrak and Mehmet Cebeci Copyright © 2014 Gökay Bayrak and Mehmet Cebeci. All rights reserved. Electron Correlation Effects on the Longitudinal Polarizabilities and Second Hyperpolarizabilities of Polyenes: A Finite Field Study Wed, 23 Jul 2014 00:00:00 +0000 We carry out ab initio calculations, based on finite-field scheme, of the longitudinal polarizabilities () and second hyperpolarizabilities () of conjugated polyenes, and study the effects of electron correlation, with second-order Moller-Plesset perturbation theory and coupled cluster with singles and doubles method. Calculations with density functional theory are also made to compare with wave-function based methods. Our study shows that electron correlation reduces linear longitudinal polarizability and enhances longitudinal second hyperpolarizability for short polyenes, but the effects decrease as the chain increases; choosing appropriate basis sets is important when quantitative results are required. Qingxu Li, Xianju Zhou, and Shiwei Yin Copyright © 2014 Qingxu Li et al. All rights reserved.