International Journal of Photoenergy The latest articles from Hindawi Publishing Corporation © 2015 , Hindawi Publishing Corporation . All rights reserved. Improved Optimization Study of Integration Strategies in Solar Aided Coal-Fired Power Generation System Mon, 03 Aug 2015 13:51:09 +0000 Solar aided coal-fired power generation system (SACFPGS) combines solar energy and traditional coal-fired units in a particular way. This study mainly improves the solar thermal storage system. Genetic algorithm is used to optimize the SACFPGS. The best integration approach of the system, the collector area, and the corresponding thermal storage capacity to replace each high-pressure extraction are obtained when the amount of coal saving in unit solar investment per hour is at its largest. System performance before and after the improvement is compared. Results show that the improvement of the thermal storage system effectively increases the economic benefit of the integrated system. Rongrong Zhai, Miaomiao Zhao, Chao Li, Pan Peng, and Yongping Yang Copyright © 2015 Rongrong Zhai et al. All rights reserved. Design and Testing of a Shell-Encapsulated Solar Collector with the Compound Surface Concentrators Mon, 03 Aug 2015 13:50:24 +0000 This paper presents design and testing of a shell-encapsulated solar collector which can be used in north area of China for wall-amounting installation. The designed solar collector is based on the combination of a novel compound curved surface concentrator and an aluminum concentric solar receiver, which is contained in a glass evacuated-tube. As there is no perforative joint between the double-skin glass evacuated-tube and the aluminum concentric solar receiver, the difficulty of vacuum keeping for a glass-metal joint is avoided. The cavity shell provides an additional thermal insulation to reduce heat loss of the designed solar collector. The working principle of the compound curved surface concentrator is described. The ray-tracing results are given to show the effect of deviation angle of the concentrator on its optical efficiency, hence determining its maximum acceptance angle. A prototype of the designed solar collector has been constructed and tested under the sunny winter weather condition. The experimental results indicate that the hot water temperature higher than 80°C with a daily average efficiency of about 45~50% has been achieved at the average ambient temperature below 0°C, so the designed solar collector can produce hot water at a useful temperature in winter. Hongfei Zheng, Gang Wu, Jing Dai, and Yanyan Ma Copyright © 2015 Hongfei Zheng et al. All rights reserved. Theoretical and Experimental Study of Spectral Selectivity Surface for Both Solar Heating and Radiative Cooling Mon, 03 Aug 2015 13:49:08 +0000 A spectral selectivity surface for both solar heating and radiative cooling was proposed. It has a high spectral absorptivity (emissivity) in the solar radiation band and atmospheric window band (i.e., 0.2~3 μm and 8~13 μm), as well as a low absorptivity (emissivity) in other bands aside from the solar radiation and atmospheric window wavelengths (i.e., 3~8 μm or above 13 μm). A type of composite surface sample was trial-manufactured combining titanium-based solar selective absorbing coating with polyethylene terephthalate (TPET). Sample tests showed that the TPET composite surface has clear spectral selectivity in the spectra of solar heating and radiation cooling wavelengths. The equilibrium temperatures of the TPET surface under different sky conditions or different inclination angles of surface were tested at both day and night. Numerical analysis and comparisons among the TPET composite surface and three other typical surfaces were also performed. These comparisons indicated that the TPET composite surface had a relative heat efficiency of 76.8% of that of the conventional solar heating surface and a relative temperature difference of 75.0% of that of the conventional radiative cooling surface, with little difference in cooling power. Mingke Hu, Gang Pei, Lei Li, Renchun Zheng, Junfei Li, and Jie Ji Copyright © 2015 Mingke Hu et al. All rights reserved. Photocorrosion Mechanism of TiO2-Coated Photoanodes Mon, 03 Aug 2015 13:09:43 +0000 Atomic layer deposition was used to coat CdS photoanodes with 7 nm thick TiO2 films to protect them from photocorrosion during photoelectrochemical water splitting. Photoelectrochemical measurements indicate that the TiO2 coating does not provide full protection against photocorrosion. The degradation of the film initiates from small pinholes and shows oscillatory behavior that can be explained by an Avrami-type model for photocorrosion that is halfway between 2D and 3D etching. XPS analysis of corroded films indicates that a thin layer of CdS remains present on the surface of the corroded photoanode that is more resilient towards photocorrosion. Arjen Didden, Philipp Hillebrand, Bernard Dam, and Roel van de Krol Copyright © 2015 Arjen Didden et al. All rights reserved. Study on a Mid-Temperature Trough Solar Collector with Multisurface Concentration Mon, 03 Aug 2015 12:59:44 +0000 A new trough solar concentrator which is composed of multiple reflection surfaces is developed in this paper. The concentrator was analyzed firstly by using optical software. The variation curves of the collecting efficiency affected by tracking error and the deviation angle were given out. It is found that the deviation tolerance for the collector tracking system is about 8 degrees when the receiver is a 90 mm flat. The trough solar concentrators were tested under real weather conditions. The experiment results indicate that, the new solar concentrator was validated to have relative good collecting efficiency, which can be more than 45 percent when it operated in more 145°C. It also has the characteristics of rdust, wind, and snow resistance and low tracking precision requirements. Zhengliang Li, Mingxian Chen, Husheng Meng, Zehui Chang, and Hongfei Zheng Copyright © 2015 Zhengliang Li et al. All rights reserved. Numerical and Experimental Study on Energy Performance of Photovoltaic-Heat Pipe Solar Collector in Northern China Mon, 03 Aug 2015 12:51:47 +0000 Several studies have found that the decrease of photovoltaic (PV) cell temperature would increase the solar-to-electricity conversion efficiency. Water type PV/thermal (PV/T) system was a good choice but it could become freezing in cold areas of Northern China. This paper proposed a simple combination of common-used PV panel and heat pipe, called PV-heat pipe (PV-HP) solar collector, for both electrical and thermal energy generation. A simplified one-dimensional steady state model was developed to study the electrical and thermal performance of the PV-HP solar collector under different solar radiations, water flow rates, and water temperatures at the inlet of manifold. A testing rig was conducted to verify the model and the testing data matched very well with the simulation values. The results indicated that the thermal efficiency could be minus in the afternoon. The thermal and electrical efficiencies decreased linearly as the inlet water temperature and water flow rate increased. The thermal efficiency increased while the electrical efficiency decreased linearly as the solar radiation increased. Hongbing Chen, Xilin Chen, Sai Chu, Lei Zhang, and Yaxuan Xiong Copyright © 2015 Hongbing Chen et al. All rights reserved. Design and Simulation of InGaN - Junction Solar Cell Thu, 30 Jul 2015 13:01:10 +0000 The tunability of the InGaN band gap energy over a wide range provides a good spectral match to sunlight, making it a suitable material for photovoltaic solar cells. The main objective of this work is to design and simulate the optimal InGaN single-junction solar cell. For more accurate results and best configuration, the optical properties and the physical models such as the Fermi-Dirac statistics, Auger and Shockley-Read-Hall recombination, and the doping and temperature-dependent mobility model were taken into account in simulations. The single-junction In0.622Ga0.378N (Eg = 1.39 eV) solar cell is the optimal structure found. It exhibits, under normalized conditions (AM1.5G, 0.1 W/cm2, and 300 K), the following electrical parameters:  mA/cm2, volts, FF = 86.2343%, and %. It was noticed that the minority carrier lifetime and the surface recombination velocity have an important effect on the solar cell performance. Furthermore, the investigation results show that the In0.622Ga0.378N solar cell efficiency was inversely proportional with the temperature. A. Mesrane, F. Rahmoune, A. Mahrane, and A. Oulebsir Copyright © 2015 A. Mesrane et al. All rights reserved. Control of the Gas Flow in an Industrial Directional Solidification Furnace for Production of High Purity Multicrystalline Silicon Ingots Sun, 26 Jul 2015 12:31:38 +0000 A crucible cover was designed as gas guidance to control the gas flow in an industrial directional solidification furnace for producing high purity multicrystalline silicon. Three cover designs were compared to investigate their effect on impurity transport in the furnace and contamination of the silicon melt. Global simulations of coupled oxygen (O) and carbon (C) transport were carried out to predict the SiO and CO gases in the furnace as well as the O and C distributions in the silicon melt. Cases with and without chemical reaction on the cover surfaces were investigated. It was found that the cover design has little effect on the O concentration in the silicon melt; however, it significantly influences CO gas transport in the furnace chamber and C contamination in the melt. For covers made of metal or with a coating on their surfaces, an optimal cover design can produce a silicon melt free of C contamination. Even for a graphite cover without a coating, the carbon concentration in the silicon melt can be reduced by one order of magnitude. The simulation results demonstrate a method to control the contamination of C impurities in an industrial directional solidification furnace by crucible cover design. Lijun Liu, Xiaofang Qi, Wencheng Ma, Zaoyang Li, and Yunfeng Zhang Copyright © 2015 Lijun Liu et al. All rights reserved. Conformational States of the Spiropyran Molecule Thu, 02 Jul 2015 12:37:27 +0000 The form of the potential surface of the ground state was investigated on the basis of indoline spiropyran. As a result of this work the rotamers of an open-ring form of the spiropyran molecule were discovered, and the existence of the most probable rotamers was justified. The 3D potential surface of the ground state of the spiropyran molecule was built. The route of the isomerization of the molecule was discovered and values of barriers for this reaction were found. The part of the isomerization route that is responsible for changing the hybridization of spiroatom from sp3 to sp2 was found. Olha Kovalenko, Petro Kondratenko, and Yuriy Lopatkin Copyright © 2015 Olha Kovalenko et al. All rights reserved. New Energy Materials and Device Application Mon, 29 Jun 2015 06:14:27 +0000 Sheng-Po Chang, Jun Zhu, Shyh-Jer Huang, Hsin-Chieh Yu, Ting-Jen Hsueh, and Hsin-Ying Lee Copyright © 2015 Sheng-Po Chang et al. All rights reserved. Power Quality Experimental Analysis on Rural Home Grid-Connected PV Systems Wed, 24 Jun 2015 11:28:32 +0000 Microgeneration is the small-scale generation of heat or electric power or both, by individuals or buildings to meet their own needs. Recently, microgeneration is being regarded as a means to decentralize the power production of renewable energies, reducing the impacts on the grid caused by unexpected energy demands. Given the increase in microgeneration facilities, determining the quantity of energy produced and the power quality assumes growing importance in low, medium, or high voltage facilities. This paper presents a power quality analysis of two different facilities with photovoltaic generation localized in a rural area of Portugal, describing the voltage and frequency behaviour, the harmonic contents, and the total harmonic distortion. Statistical data are presented regarding the number of voltage events and occurrence of dips and swells in both facilities as a percentage of rated voltage. We conclude that some PV systems can severely affect voltage quality, forcing the grid to work at and even above the maximum voltage standard limit. Rita Jorge Cerqueira Pinto, Sílvio José Pinto Simões Mariano, and Maria do Rosário Alves Calado Copyright © 2015 Rita Jorge Cerqueira Pinto et al. All rights reserved. Optimization of μc-Si1−xGex:H Single-Junction Solar Cells with Enhanced Spectral Response and Improved Film Quality Wed, 24 Jun 2015 07:14:42 +0000 Effects of RF power on optical, electrical, and structural properties of μc-Si1−xGex:H films was reported. Raman and FTIR spectra from μc-Si1−xGex:H films reflected the variation in microstructure and bonding configuration. Unlike increasing the germane concentration for Ge incorporation, low RF power enhanced Ge incorporation efficiency in μc-Si1−xGex:H alloy. By decreasing RF power from 100 to 50 W at a fixed reactant gas ratio, the optical bandgap of μc-Si1−xGex:H was reduced owing to the increase in Ge content from 11.2 to 23.8 at.%, while Ge-related defects and amorphous phase were increased. Consequently, photo conductivity of 1.62 × 10−5 S/cm was obtained for the μc-Si1−xGex:H film deposited at 60 W. By applying 0.9 μm thick μc-Si1−xGex:H absorber with of 48% and [Ge] of 16.4 at.% in the single-junction cell, efficiency of 6.18% was obtained. The long-wavelength response of μc-Si1−xGex:H cell was significantly enhanced compared with the μc-Si:H cell. In the case of tandem cells, 0.24 μm a-Si:H/0.9 μm μc-Si1−xGex:H tandem cell exhibited a comparable spectral response as 0.24 μm a-Si:H/1.4 μm μc-Si:H tandem cell and achieved an efficiency of 9.44%. Yen-Tang Huang, Pei-Ling Chen, Po-Wei Chen, Hung-Jung Hsu, Cheng-Hang Hsu, and Chuang-Chuang Tsai Copyright © 2015 Yen-Tang Huang et al. All rights reserved. Modeling and Maximum Power Point Tracking Techniques of Photovoltaic Systems Thu, 18 Jun 2015 06:35:06 +0000 Marcelo Cabral Cavalcanti, Francisco de Assis dos Santos Neves, Denizar Cruz Martins, Emilio José Bueno Peña, and Euzeli Cipriano dos Santos Júnior Copyright © 2015 Marcelo Cabral Cavalcanti et al. All rights reserved. Superior Photocurrent of Quantum Dot Sensitized Solar Cells Based on PbS : In/CdS Quantum Dots Wed, 17 Jun 2015 07:28:23 +0000 PbS : In and CdS quantum dots (QDs) are sequentially assembled onto a nanocrystalline TiO2 film to prepare a PbS : In/CdS cosensitized photoelectrode for QD sensitized solar cells (QDSCs). The results show that PbS : In/CdS QDs have exhibited a significant effect in the light harvest and performance of the QDSC. In the cascade structure of the electrode, the reorganization of energy levels between PbS and TiO2 forms a stepwise structure of band-edge levels which is advantageous to the electron injection into TiO2. Energy conversion efficiency of 2.3% is achieved with the doped electrode, under the illumination of one sun (AM1.5, 100 mW cm2). Besides, a remarkable short circuit current density (up to 23 mA·cm−2) is achieved in the resulting PbS : In/CdS quantum dot sensitized solar cell, and the related mechanism is discussed. Zongbo Huang and Xiaoping Zou Copyright © 2015 Zongbo Huang and Xiaoping Zou. All rights reserved. Maximum Power Point Tracking Based on Sliding Mode Control Tue, 16 Jun 2015 14:26:34 +0000 Solar panels, which have become a good choice, are used to generate and supply electricity in commercial and residential applications. This generated power starts with the solar cells, which have a complex relationship between solar irradiation, temperature, and output power. For this reason a tracking of the maximum power point is required. Traditionally, this has been made by considering just current and voltage conditions at the photovoltaic panel; however, temperature also influences the process. In this paper the voltage, current, and temperature in the PV system are considered to be a part of a sliding surface for the proposed maximum power point tracking; this means a sliding mode controller is applied. Obtained results gave a good dynamic response, as a difference from traditional schemes, which are only based on computational algorithms. A traditional algorithm based on MPPT was added in order to assure a low steady state error. Nimrod Vázquez, Yuz Azaf, Ilse Cervantes, Eslí Vázquez, and Claudia Hernández Copyright © 2015 Nimrod Vázquez et al. All rights reserved. MPPT Technique Based on Current and Temperature Measurements Tue, 16 Jun 2015 12:49:22 +0000 This paper presents a new maximum power point tracking (MPPT) method based on the measurement of temperature and short-circuit current, in a simple and efficient approach. These measurements, which can precisely define the maximum power point (MPP), have not been used together in other existing techniques. The temperature is measured with a low cost sensor and the solar irradiance is estimated through the relationship of the measured short-circuit current and its reference. Fast tracking speed and stable steady-state operation are advantages of this technique, which presents higher performance when compared to other well-known techniques. Eduardo Moreira Vicente, Robson Luiz Moreno, and Enio Roberto Ribeiro Copyright © 2015 Eduardo Moreira Vicente et al. All rights reserved. A New Fractional-Order Based Intelligent Maximum Power Point Tracking Control Algorithm for Photovoltaic Power Systems Tue, 16 Jun 2015 12:48:30 +0000 This paper proposes a new type of variable fractional-order incremental conductance algorithm (VFOINC), combined with extenics variable step size (EVSS) control into the maximum power point tracking (MPPT) design for photovoltaic power systems. At the beginning of maximum power tracking, the fractional-order number is selected as 1; the good transient tracking characteristic of traditional incremental conductance method is used. When the maximum power point is approached, the fractional-order number is selected as variable fractional order; the curve profile of in fractional order is used to approximate, so that the system has good tracking effect in transient and steady states. The experimental and simulation results show that, compared with traditional incremental conductance method (INC) and fractional-order incremental conductance method (FOINC), this method has better MPPT effect. Kuo-Nan Yu, Chih-Kang Liao, and Her-Terng Yau Copyright © 2015 Kuo-Nan Yu et al. All rights reserved. Biaxial Solar Tracking System Based on the MPPT Approach Integrating ICTs for Photovoltaic Applications Tue, 16 Jun 2015 12:36:50 +0000 The smart grid and distributed generation based on renewable energy applications often involve the use of information and communication technology (ICT) coupled with advanced control and monitoring algorithms to improve the efficiency and reliability of the electrical grid and renewable generation systems. Photovoltaic (PV) systems have been recently applied with success in the fields of distributed generation due to their lower environmental impact where the electrical energy generation is related to the amount of solar irradiation and thus the angle of incident ray of the sun on the surface of the modules. This paper introduces an integration of ICTs in order to achieve the maximum power point tracking (MPPT) using a biaxial solar tracking system for PV power applications. To generate the references for the digital control of azimuth and elevation angles a Global Positioning System (GPS) by satellites is used which enables acquiring the geographic coordinates of the sun in real-time. As a total integration of the system a communication platform based on the 802.15.4 protocol for the wireless sensor networks (WSNs) is adopted for supervising and monitoring the PV plant. A 2.4 kW prototype system is implemented to validate the proposed control scheme performance. Raúl Gregor, Yoshihiko Takase, Jorge Rodas, Leonardo Carreras, Derlis Gregor, and Andrés López Copyright © 2015 Raúl Gregor et al. All rights reserved. Investigating the Effect of Piezoelectric Polarization on GaN-Based LEDs with Different Prestrain Layer by Temperature-Dependent Electroluminescence Tue, 16 Jun 2015 12:17:18 +0000 The effect of piezoelectric polarization on GaN-based light emitting diodes (LEDs) with different kinds of prestrain layers between the multiple quantum wells (MQWs) and n-GaN layer is studied and demonstrated. Compared with the conventional LED, more than 10% enhancement in the output power of the LED with prestrain layer can be attributed to the reduction of polarization field within MQWs region. In this study, we reported a simple method to provide useful comparison of polarization fields within active region in GaN-based LEDs by using temperature-dependent electroluminescence (EL) measurement. The results pointed out that the polarization field of conventional LED was stronger than that of the others due to larger variation of the wavelength transition position (i.e., blue-shift change to red-shift) from 300 to 350 K, and thus the larger polarization field must be effectively screened by injecting more carriers into the MQWs region. C. K. Wang, Y. Z. Chiou, T. H. Chiang, and T. K. Lin Copyright © 2015 C. K. Wang et al. All rights reserved. Photovoltaic Array Reconfiguration Strategy for Maximization of Energy Production Tue, 16 Jun 2015 10:28:10 +0000 This paper presents a dynamic reconfiguration method for electrical connections in a Series-Parallel connected photovoltaic array under partial shading conditions. It is desirable to extract the maximum energy from the array, but it does not occur in situations where the modules have different points of operation caused by shading. The proposed method is then characterized by the maintenance of the PV array dimensions, that is; no module is removed or added to the array. Furthermore, the control algorithm is based on the Rough Sets Theory, which allows the fast and efficient implementation of a control system, comprising rules that identify the system optimal configuration. Paula dos Santos Vicente, Tales Cleber Pimenta, and Enio Roberto Ribeiro Copyright © 2015 Paula dos Santos Vicente et al. All rights reserved. An Ultrafast Maximum Power Point Setting Scheme for Photovoltaic Arrays Using Model Parameter Identification Tue, 16 Jun 2015 09:25:09 +0000 Maximum power point tracking (MPPT) for photovoltaic (PV) arrays is essential to optimize conversion efficiency under variable and nonuniform irradiance conditions. Unfortunately, conventional MPPT algorithms such as perturb and observe (P&O), incremental conductance, and current sweep method need to iterate command current or voltage and frequently operate power converters with associated losses. Under partial overcast conditions, tracking the real MPP in multipeak P-I or P-V curve model becomes highly challenging, with associated increase in search time and converter operation, leading to unnecessary power being lost in the MPP tracking process. In this paper, the noted drawbacks in MPPT-controlled converters are addressed. In order to separate the search algorithms from converter operation, a model parameter identification approach is presented to estimate insolation conditions of each PV panel and build a real-time overall P-I curve of PV arrays. Subsequently a simple but effective global MPPT algorithm is proposed to track the MPP in the overall P-I curve obtained from the identified PV array model, ensuring that the converter works at the MPP. The novel MPPT is ultrafast, resulting in conserved power in the tracking process. Finally, simulations in different scenarios are executed to validate the novel scheme’s effectiveness and advantages. Zhaohui Cen Copyright © 2015 Zhaohui Cen. All rights reserved. A Reinforcement Learning-Based Maximum Power Point Tracking Method for Photovoltaic Array Tue, 16 Jun 2015 09:23:40 +0000 A reinforcement learning-based maximum power point tracking (RLMPPT) method is proposed for photovoltaic (PV) array. By utilizing the developed system model of PV array and configuring the environment for the reinforcement learning, the proposed RLMPPT method is able to observe the environment state of the PV array in the learning process and to autonomously adjust the perturbation to the operating voltage of the PV array in obtaining the best MPP. Simulations of the proposed RLMPPT for a PV array are conducted. Experimental results demonstrate that, in comparison to an existing MPPT method, the RLMPPT not only achieves better efficiency factor for both simulated weather data and real weather data but also adapts to the environment much fast with very short learning time. Roy Chaoming Hsu, Cheng-Ting Liu, Wen-Yen Chen, Hung-I Hsieh, and Hao-Li Wang Copyright © 2015 Roy Chaoming Hsu et al. All rights reserved. Hydrothermal Growth of Quasi-Monocrystal ZnO Thin Films and Their Application in Ultraviolet Photodetectors Tue, 16 Jun 2015 07:16:48 +0000 Quasi-monocrystal ZnO film grown using the hydrothermal growth method is used for the fabrication of Cu2O/ZnO heterojunction (HJ) ultraviolet photodetectors (UV-PDs). The HJ was formed via the sputtering deposition of p-type Cu2O onto hydrothermally grown ZnO film (HTG-ZnO-film). The effect of annealing temperature in the nitrogen ambient on the photoluminescence spectra of the synthesized ZnO film was studied. The optoelectronic properties of Cu2O/ZnO film with various Cu2O thicknesses (250–750 nm) under UV light (365 nm; intensity: 3 mW/cm2) were determined. The UV sensitivity of the HTG-ZnO-film-based UV-PDs and the sputtered ZnO-film-based UV-PDs were 55.6-fold () and 8.8-fold (), respectively. The significant gain in sensitivity ( = 630%) of the proposed ZnO-film-based device compared to that for the device based on sputtered film can be attributed to the improved photoelectric properties of quasi-monocrystal ZnO film. Yung-Chun Tu, Shui-Jinn Wang, Tseng-Hsing Lin, Chien-Hsiung Hung, Tsung-Che Tsai, Ru-Wen Wu, Kai-Ming Uang, and Tron-Min Chen Copyright © 2015 Yung-Chun Tu et al. All rights reserved. Scalability of Phase Change Materials in Nanostructure Template Tue, 16 Jun 2015 07:15:32 +0000 The scalability of In2Se3, one of the phase change materials, is investigated. By depositing the material onto a nanopatterned substrate, individual In2Se3 nanoclusters are confined in the nanosize pits with well-defined shape and dimension permitting the systematic study of the ultimate scaling limit of its use as a phase change memory element. In2Se3 of progressively smaller volume is heated inside a transmission electron microscope operating in diffraction mode. The volume at which the amorphous-crystalline transition can no longer be observed is taken as the ultimate scaling limit, which is approximately 5 nm3 for In2Se3. The physics for the existence of scaling limit is discussed. Using phase change memory elements in memory hierarchy is believed to reduce its energy consumption because they consume zero leakage power in memory cells. Therefore, the phase change memory applications are of great importance in terms of energy saving. Wei Zhang, Biyun L. Jackson, Ke Sun, Jae Young Lee, Shyh-Jer Huang, Hsin-Chieh Yu, Sheng-Po Chang, Shoou-Jinn Chang, and Ya-Hong Xie Copyright © 2015 Wei Zhang et al. All rights reserved. An Accurate Thermoviscoelastic Rheological Model for Ethylene Vinyl Acetate Based on Fractional Calculus Mon, 15 Jun 2015 12:40:25 +0000 The thermoviscoelastic rheological properties of ethylene vinyl acetate (EVA) used to embed solar cells have to be accurately described to assess the deformation and the stress state of photovoltaic (PV) modules and their durability. In the present work, considering the stress as dependent on a noninteger derivative of the strain, a two-parameter model is proposed to approximate the power-law relation between the relaxation modulus and time for a given temperature level. Experimental validation with EVA uniaxial relaxation data at different constant temperatures proves the great advantage of the proposed approach over classical rheological models based on exponential solutions. Marco Paggi and Alberto Sapora Copyright © 2015 Marco Paggi and Alberto Sapora. All rights reserved. Improving Crystalline Silicon Solar Cell Efficiency Using Graded-Refractive-Index SiON/ZnO Nanostructures Mon, 15 Jun 2015 12:08:16 +0000 The fabrication of silicon oxynitride (SiON)/ZnO nanotube (NT) arrays and their application in improving the energy conversion efficiency (η) of crystalline Si-based solar cells (SCs) are reported. The SiON/ZnO NT arrays have a graded-refractive-index that varies from 3.5 (Si) to (Si3N4 and ZnO) to (SiON) to 1 (air). Experimental results show that the use of 0.4 μm long ZnO NT arrays coated with a 150 nm thick SiON film increases by 39.2% under AM 1.5 G (100 mW/cm2) illumination as compared to that of regular SCs with a Si3N4/micropyramid surface. This enhancement can be attributed to SiON/ZnO NT arrays effectively releasing surface reflection and minimizing Fresnel loss. Yung-Chun Tu, Shui-Jinn Wang, Chien-Hung Wu, Kow-Ming Chang, Tseng-Hsing Lin, Chien-Hsiung Hung, and Jhen-Siang Wu Copyright © 2015 Yung-Chun Tu et al. All rights reserved. Optical Properties of Indium Doeped ZnO Nanowires Mon, 15 Jun 2015 12:06:06 +0000 We report the synthesis of the ZnO nanowires (NWs) with different indium concentrations by using the thermal evaporation method. The gold nanoparticles were used as the catalyst and were dispersed on the silicon wafer to facilitate the growth of the ZnO NWs. High resolution transmission electron microscopy confirms that the ZnO NWs growth relied on vapor-liquid-solid mechanism and energy dispersion spectrum detects the atomic percentages of indium in ZnO NWs. Scanning electron microscopy shows that the diameters of pure ZnO NWs range from 20 to 30 nm and the diameters of ZnO:In were increased to 50–80 nm with increasing indium doping level. X-ray diffraction results point out that the crystal quality of the ZnO NWs was worse with doping higher indium concentration. Photoluminescence (PL) study of the ZnO NWs exhibited main photoemission at 380 nm due to the recombination of excitons in near-band-edge (NBE). In addition, PL results also indicate the slightly blue shift and PL intensity decreasing of NBE emission from the ZnO NWs with higher indium concentrations could be attributed to more donor-induced trap center generations. Tsung-Shine Ko, Sin-Liang Ou, Kuo-Sheng Kao, Tz-Min Yang, and Der-Yuh Lin Copyright © 2015 Tsung-Shine Ko et al. All rights reserved. Optoelectric Properties of GaInP p-i-n Solar Cells with Different i-Layer Thicknesses Mon, 15 Jun 2015 11:58:24 +0000 The optoelectric properties of GaInP p-i-n solar cells with different intrinsic layer (i-layer) thicknesses from 0.25 to 1 μm were studied. Both emission intensity and full width at half maximum features of the photoluminescence spectrum indicate that the optimum i-layer thickness would be between 0.5 and 0.75 μm. The integrated current results of photocurrent experiment also point out that the samples with 0.5 to 0.75 μm i-layer thicknesses have optimum value around 156 nA. Electroreflectance measurements reveal that the built-in electric field strength of the sample gradually deviates from the theoretical value larger when i-layer thickness of the sample is thicker than 0.75 μm. I-V measurements also confirm crystal quality for whole samples by obtaining the information about short currents of photovoltaic performances. A series of experiments reflect that thicker i-layer structure would induce more defects generation lowering crystal quality. Tsung-Shine Ko, Der-Yuh Lin, You-Chi He, Chen-Chia Kao, Bo-Yuan Hu, Ray-Hua Horng, Fan-Lei Wu, Chih-Hung Wu, and Yu-Li Tsai Copyright © 2015 Tsung-Shine Ko et al. All rights reserved. Plasmon-Enhanced Photoluminescence of an Amorphous Silicon Quantum Dot Light-Emitting Device by Localized Surface Plasmon Polaritons in Ag/SiOx:a-Si QDs/Ag Sandwich Nanostructures Mon, 15 Jun 2015 11:52:25 +0000 We investigated experimentally the plasmon-enhanced photoluminescence of the amorphous silicon quantum dots (a-Si QDs) light-emitting devices (LEDs) with the :a-Si QDs/Ag sandwich nanostructures, through the coupling between the a-Si QDs and localized surface plasmons polaritons (LSPPs) mode, by tuning a one-dimensional (1D) Ag grating on the top. The coupling of surface plasmons at the top and bottom :a-Si QDs interfaces resulted in the localized surface plasmon polaritons (LSPPs) confined underneath the Ag lines, which exhibit the Fabry-Pérot resonance. From the Raman spectrum, it proves the existence of a-Si QDs embedded in Si-rich film (:a-Si QDs) at a low annealing temperature (300°C) to prevent the possible diffusion of Ag atoms from Ag film. The photoluminescence (PL) spectra of a-Si QDs can be precisely tuned by a 1D Ag grating with different pitches and Ag line widths were investigated. An optimized Ag grating structure, with 500 nm pitch and 125 nm Ag line width, was found to achieve up to 4.8-fold PL enhancement at 526 nm and 2.46-fold PL integrated intensity compared to the a-Si QDs LEDs without Ag grating structure, due to the strong a-Si QDs-LSPPs coupling. Tsung-Han Tsai, Ming-Yi Lin, Wing-Kit Choi, and Hoang Yan Lin Copyright © 2015 Tsung-Han Tsai et al. All rights reserved. Effects of Sheet Resistance on mc-Si Selective Emitter Solar Cells Using Laser Opening and One-Step Diffusion Sun, 14 Jun 2015 12:20:47 +0000 In order to simplify process procedure and improve conversion efficiency (η), we present new steps of laser opening and one-step POCl3 diffusion to fabricate selective emitter (SE) solar cells, in which heavily doped regions (HDR) and lightly doped regions (LDR) were formed simultaneously. For HDR, we divided six cells into two groups for POCl3 diffusion with sheet resistance () of 40 Ω/sq (for group A) and 50 Ω/sq (for group B). The dry oxidation duration at a temperature of 850°C was 18, 25, and 35 min for the 3 different cells in each group. This created six SE samples with different pairings for the HDR and LDR. The optimal cell (sample SE2) with values of 40/81 Ω/Sq in HDR/LDR showed the best η of 16.20%, open circuit voltage () of 612.52 mV, and fill factor (FF) of 75.83%. The improvement ratios are 1.57% for η and 14.32% for external quantum efficiency (EQE) as compared with those of the two-step diffusion process of our previous study. Moreover, the one-step laser opening process and omitting the step of removing the damage caused by laser ablation especially reduce chemistry pollution, thus showing ecofriendly process for use in industrial-scale production. Sheng-Shih Wang, Jyh-Jier Ho, Jia-Jhe Liou, Jia-Show Ho, Song-Yeu Tsai, Hsien-Seng Hung, Chi-Hsiao Yeh, and Kang L. Wang Copyright © 2015 Sheng-Shih Wang et al. All rights reserved.