Effectively extending visible light absorption with a broad spectrum sensitizer for improving the H2 evolution of in-situ Cu/g-C3N4 nanocomponents

Photocatalysts with broad spectrum absorption have been desired for a long time due to their ability to absorb more visible light. Herein, we developed an in-situ approach to specifically fabricate Cu nanoparticles onto the exterior surface of g-C₃N₄, followed by sensitization with Erythrosin B, to improve the photocatalytic H₂ evolution of g-C₃N₄ and extend the spectrum absorption. The photocatalytic H₂ evolution rate was significantly promoted, to more than 26 times that of pure g-C₃N₄, and the photocatalytic ability was maintained until reaching a wavelength of 700 nm. The origin of the improved activity was attributed to an in-situ Cu nanoparticle modification, which acts as an electron reservoir, and dye sensitization, which could extend the range of the visible light absorption, preventing charge recombination and enhancing the visible light utilization efficiency. In addition, the photocatalytic stability was investigated, and no significant attenuation was detected after six recycles.     

Angle-dependent XPS analysis of silicon nitride film deposited on screen-printed crystalline silicon solar cell

In this work silicon nitride (Si₃N₄) film was deposited as an antireflection coating (ARC) on crystalline silicon solar cell (cell?A) using plasma-enhanced chemical vapor deposition (PECVD). Two solar cells XA and XB of approximately equal area were diced from cell#A and characterized by angle-dependent X-ray photoelectron spectroscopy (XPS). The XPS profiling shows the presence of silicon (Si), nitrogen (N), carbon (C) and oxygen (O) in the Si₃N₄ film. The presence of C and O indicates that organic substances, involved in processing steps were not released completely from the surface and may diffuse in Si₃N₄ ARC during deposition. The XPS spectra corresponding to Si2p, N1s, C1s and O1s were recorded at angles 0° (normal to the surface), 30° and 45°, as angle increases spectra becomes more surface sensitive. Peak positions in Si2p and N1s spectra explain the oxygen contamination in the Si₃N₄ film. The shift in the peak positions of C1s and O1s as angle increases from 0° to 45° explains the surface contamination of carbon and oxygen. The atomic composition of elements Si, N, C and O show more carbon, oxygen concentration and smaller N/Si ratio than stoichiometry, i.e. Si₃N₄ in cell XB. However, cell XA not only show better photovoltaic performance in terms of parameters open-circuit voltage (V_oc), short-circuit current density (J_sc), fill factor (FF) and efficiency (η) but also have more uniform texturization and regular pyramids on the surface as revealed by scanning electron microscopy (SEM). The presence of higher concentration of impurities (carbon and oxygen), non-uniformity in texturization and in the Si₃N₄ film as well could be responsible for less satisfactory photovoltaic performance of cell XB.     

Theoretical analysis of the optimum energy band gap of semiconductors for fabrication of solar cells for applications in higher latitudes locations

In this work some results of theoretical analysis on the selection of optimum band gap semiconductor absorbers for application in either single or multijunction (up to five junctions) solar cells are presented. For calculations days have been taken characterized by various insolation and ambient temperature conditions defined in the draft of the IEC 61836 standard (Performance testing and energy rating of terrestrial photovoltaic modules) as a proposal of representative set of typical outdoor conditions that may influence performance of photovoltaic devices. Besides various irradiance and ambient temperature ranges, these days additionally differ significantly regarding spectral distribution of solar radiation incident onto horizontal surface. Taking these spectra into account optimum energy band gaps and maximum achievable efficiencies of single and multijunction solar cells made have been estimated. More detailed results of analysis performed for double junction cell are presented to show the effect of deviations in band gap values on the cell efficiency.     

A computer analysis of double junction solar cells with a-Si : H absorber layers

An integrated electrical-optical model has been used to examine the design of double junction solar cells, where the component cells have a-Si : H absorber layers of identical material quality in the initial state. The model takes into account both specular interference effects; and diffused reflectances and transmittances due to interface roughness. The carrier transport at the junction between the two p–i–n subcells is simulated with the help of a thin heavily defective “recombination” layer with a reduced mobility gap.Analysis of the transport properties as a function of position in the device indicates that for the highest double junction cell efficiency the thicknesses of the absorber layers of the component subcells are such that the electric fields over these absorber layers are high simultaneously. Our results also show that whereas in the initial state, the open-circuit voltage and the fill factor of the double junction cell are heavily dependent on the electric field in the thicker bottom subcell; in the light-stabilised state, the more degraded top subcell plays an important role in limiting double junction cell performance. The quantum efficiency under AM 1.5 bias light has been shown to be very sensitive to thickness variations of the component subcells. Using this tool we have arrived at a simplified procedure for designing the double junction structure likely to exhibit the highest efficiency in the stabilised state.     

Experimental studies and limitations of the light trapping and optical losses in microcrystalline silicon solar cells

This study addresses the potential of different approaches to improve the generated current in silicon thin-film solar cells and modules. Decreasing the carrier concentration in the front contact has proven to increase the quantum efficiency and the cell-current density significantly. Additionally, an optically improved ZnO/Ag back reflector and the optimized light incoupling by anti-reflection layers were studied. In this contribution, we show the potential of the different optical components and discuss combinations thereof in order to obtain a maximized cell-current density in silicon thin-film solar cells. Limitations of the cell-current density are discussed with respect to theoretical calculations.     

Experimental analysis and exergy efficiency of a conventional solar still with Fresnel lens and energy storage material

This study focuses on the experimental investigation and exergy analysis of a modified solar still (MSS) with convex lenses on glass cover to collect the solar radiation at the focus on surface water. A comparative analysis of the performance and yield of the MSS with convex lenses and the conventional single slope SS were carried out for the same climatic condition of Tanta (Egypt). Similarly, the effect of modification in the SS using convex lenses, with or without black stones, on the freshwater yield is experimentally investigated. The results indicated that the lenses focus the solar radiation to the water placed in the basin and increase the water‐glass temperature difference (T _w – T _g). The yield of freshwater from the MSS with the convex lenses is comparatively higher than that of the conventional SS (26.64%). In addition to convex lenses in the inner cover surface, freshwater yield improved by 35.55% by adding blue stones as energy material inside the basin under constant water mass of 30 kg. The maximum exergy efficiency of the SS with lenses and blue stones was 11.7%, while the SS with lenses alone was 4%. The quality of freshwater produced after desalination was well within the World Health Organization standards. The total dissolved solids and pH after desalination were 22 mg/L and 8.08, respectively.     

Optical and electronic simulation of gallium arsenide/silicon tandem four terminal solar cells

A tandem solar cell in a mechanical (stack like) arrangement of gallium arsenide and silicon solar cells is evaluated as a pathway towards higher efficiency terrestrial solar cells. In this work the technical feasibility of the tandem solar cell is investigated. Here we report on detailed electrical and optical simulations of this structure quantifying various theoretical and practical loss mechanisms in the interface and in the device and indicate that an efficiency improvement of 5.13% would be attainable with the present generation of gallium arsenide and silicon solar cells in this configuration. The optical and electrical parameters for gallium arsenide and silicon simulation models were extracted from experimental devices and material vendors. The developed simulation models were validated by comparing the performance of standalone gallium arsenide and silicon solar cells with experimental devices reported in the literature.     

Thermal and electrical performance analysis of silicon vertical multi-junction solar cell under non-uniform illumination

The silicon vertical multi-junction (VMJ) solar cell has low costs and low series resistance, thus it has a good potential in concentration photovoltaics. However, there were few discussions about the thermal and electrical performance of silicon VMJ cell under non-uniform illumination. In this work, the thermal performance of silicon VMJ cell under 1D non-uniform illumination of 500 suns was calculated using finite element method first, and then the electrical performance of the cell was calculated using SPICE software based on the thermal simulation results. It was found that the mean temperature of the cell increased with the degree of non-uniform illumination when the area ratio of the sink to the cell was 500X, and the mean temperature changed few when the area ratio was 2500X. The efficiency of the cell did not decrease with the increase of the degree of non-uniform illumination when the area ratio was 500X, and the efficiency increased with the degree of non-uniform illumination when the area ratio was 2500X. Thus, the silicon VMJ cell had better performance than silicon planar junction cell under 1D non-uniform illumination of 500 suns.     

An analysis of the electrical characteristics of DSC under inhomogeneous solar illumination

A simple model to describe the dye sensitized solar cell (DSC) is presented in which simultaneous occurrence of diffusion and charge transfer processes, power loss due to inhomogeneous excitation resulted from absorption of the dye and the electrolyte, and power gain due to the direct excitation (not via dye molecules) of semiconductor particles are taken into consideration. About 35% and 2.2% decrease in power is estimated for the dye and the electrolyte absorption, respectively, while 2.9% increase of power is obtained by the direct excitation of TiO₂ at maximum power point (MPP) under AM1.5 solar illumination. Some numerical results are also presented to demonstrate the influence of the material parameters for the cell characteristics.     

Experimental and economic analysis of energy storage-based single-slope solar still with hollow-finned absorber basin

The paucity of drinking water is an alarming glitch across the globe. The conversion of available seawater into drinking water by utilizing renewable energy is the best way to surmount this challenge. Desalination through solar still is one of the notable, monetary, and viable processes among various desalination approaches. The current research aims to augment the potable water yield of single-slope solar still by using a hollow-finned absorber basin inserted into paraffin wax—phase change material (PCM). The effect of hollow-finned absorber basin on the yield of solar still is investigated separately, with and without PCM, and compared with the results of conventional solar still (CSS). In the first set of experiments, the CSS and solar still with a hollow-finned absorber basin without PCM (SSHF) are investigated. In the second set of experiments, the CSS and solar still with a hollow-finned absorber basin inserted into PCM (SSHFP) are investigated. The experimental results reported that the CSS is having almost the same yield on the 2 days of testing. The yield of SSHF and SSHFP is increased by 15.7% and 52.4%, respectively, when compared with CSS. The results of the economic analysis proved that the payback period and cost per liter of freshwater produced from SSHFP are comparatively better than SSHF and CSS.     

Influence of deep level defects on the performance of crystalline silicon solar cells: Experimental and simulation study

Introduction of deep level defects during thermal diffusion of phosphorous (P) in silicon (Si) using spin-on-doping (SOD) from phosphosilicate glass (PSG) was studied using deep level transient spectroscopy (DLTS). The structure was utilized as a solar cell and defect-induced-degradation of the cell efficiency was studied and modeled. The light current-voltage (LIV) measurements performed on as-fabricated solar cell yielded open circuit voltage, short-circuit current density, fill factor (FF) and efficiency to be 540 mV, 24 mA/cm², 40% and 5%, respectively. Whilst the simulation of the similar solar cell using AFORS-HET software revealed significantly higher data than the experimental ones. However, by including three deep level defects H₁-H₃ (holes) having activation energies (eV) 0.23, 0.33 and 0.41 in the modeled solar cell, the simulated results were observed in remarkably good agreement with experimental data. Our DLTS measurements practically witnessed H₁-H₃ defect levels in p-layer of the cell.     

太阳电池最大功率及其跟踪模式

根据太阳电池电流方程及输出功率极值条件,在温度保持不变时,可建立最大功率方程,由此可在伏安特性坐标系内绘制大范围光照变化时最大功率的轨迹线,发现其呈现为S形状。据此提出三种最大功率的跟踪模式:(1)恒载跟踪;(2)恒压跟踪;(3)计算跟踪。其中恒载跟踪适用极低光照和极强光照,恒压跟踪适合于中等光照,计算跟踪适合于恒压跟踪向恒载跟踪的过渡光强。计算跟踪是本文给出的一种最大功率电压联立求解的计算方法。     

Design and analysis of an integrated concentrated solar and wind energy system with storage

This study analyzes a renewable energy‐driven innovative multigeneration system, in which wind and solar energy sources are utilized in an efficient way to generate several useful commodities such as hydrogen, oxygen, desalted water, space cooling, and space heating along with electricity. A 1‐km² heliostat field is considered to concentrate the solar light onto a spectrum splitter, where the light spectrum is separated into two portions as reflected and transmitted to be used as the energy source in the concentrated solar power (CSP) and concentrated photovoltaics (CPV) receivers, respectively. As such, CSP and CPV systems are integrated. Wind energy is proposed for generating electricity (146 MW) or thermal energy (138 MW) to compensate the energy need of the multigeneration system when there is insufficient solar energy. In addition, multiple commodities, 46 MW of electricity, 12 m³/h of desalted water, and 69 MW of cooling, are generated using the Rankine cycle and the rejected heat from its condenser. Further, the heat generated on CPV cells is recovered for efficient photovoltaic conversion and utilized in the space heating (34 MW) and proton exchange membrane (PEM) electrolyzer (239 kg/h) for hydrogen production. The energy and exergy efficiencies of the overall system are calculated as 61.3% and 47.8%, respectively. The exergy destruction rates of the main components are presented to identify the potential improvements of the system. Finally, parametric studies are performed to analyze the effect of changing parameters on the exergy destruction rates, production rates, and efficiencies.     

Maximum efficiencies and parametric optimum designs of concentrating photovoltaic cell/heat engine systems with three‐band spectrum split

The irreversible model of a concentrating photovoltaic cell/heat engine system with three‐band spectrum splitting is established for the further prediction of the conversion efficiency of photovoltaic/thermal systems, in which the internal and external irreversible losses are considered. An update efficiency of the spectrum splitting system is derived, from which the maximum efficiency of the whole system is calculated. The influences of the area ratio of two subsystems on the systemic performance are analyzed in detail. The reasonable ranges of the area ratio are given. The maximum efficiency and the corresponding critical parameters are obtained under different operating conditions. It is found that the introduction of the area ratio is significant for accurate predictions of systemic performances and the maximum efficiency can attain 77.64%, which significantly exceeds that of an individual concentrating photovoltaic cell and solar‐driven heat engine at the same concentration condition. The performance characteristics of the two‐band spectrum splitting system including the photovoltaic cell and heat engine may be directly obtained from the present model. Moreover, the performances of three‐ and two‐band spectrum splitting systems are compared, and consequently, the advantages of the three‐band spectrum splitting system are revealed.     

Temperature dependence of I-V characteristics and performance parameters of silicon solar cell

The temperature dependence of open-circuit voltage (V_oc) and curve factor (CF) of a silicon solar cell has been investigated in temperature range 295-320 K. The rate of decrease of V_oc with temperature (T) is controlled by the values of the band gap energy (E_g), shunt resistance (R_sh) and their rates of change with T. We have found that R_sh decreases nearly linearly with T and its affect on dV_oc/dT is significant for cells having smaller R_sh values. Series resistance also changes nearly linearly with voltage. CF depends not only on the value of R_s and other parameters but also on the rate of change of R_s with voltage. The rate of decrease of R_s with voltage and T are important to estimate the value of CF and its decrease with temperature accurately.     

单晶硅太阳电池在槽式聚光与普通光照条件下伏安特性的对比研究

为进一步对开发聚光热电联供系统提供依据与指导,在槽式聚光器中,设计了槽式单晶硅太阳能电池热电联供测试系统,并在太阳聚光条件下对单晶硅太阳电池进行了伏安特性的测试.测试结果表明,普通单晶硅太阳能电池在聚光10倍左右的情况下,开路电压变化不大,开路电流放大了4.1倍左右,伏安特性曲线基本满足线性关系.     

配合集热器的盐梯度太阳池热性能实验与分析

构建表面积为1.50 m×1.50 m的小型实验用盐梯度太阳池,并与平板太阳能集热器配合使用,分别对普通太阳池和集热增强型太阳池进行了储热、放热实验。实验研究与理论分析表明:单独盐梯度太阳池的放热量为3.5×103k J,热效率为13.6%;集热增强型太阳池放热量可以达到4.8×103k J,且热效率增至28.1%。另外后者下对流层温度最高可提升10℃以上,从而证明太阳能集热器可以有效提高太阳池热效率,增加下对流层储热量。此外,考虑了放热过程换热器对太阳池下对流层的扰动,对比实验前后的溶液浓度,可以看出实验后太阳池盐度曲线合理,非对流层呈良好梯度分布,太阳池稳定性并未遭到破坏。     

Experimental validation of glazed hybrid micro-channel solar cell thermal tile

In this communication, an attempt has been made to evaluate the theoretical performance of a glazed hybrid micro-channel solar cell thermal (MCSCT) tile. Experiment has been performed in indoor condition and it has been observed that there is good agreement between theoretical and experimental values with correlation coefficient and root mean square percentage deviation in range of 0.995–0.998 and 3.21–4.50 respectively. Effect of design parameters on different combination (series and parallel) of glazed hybrid MCSCT tile for Srinagar climatic condition, India has also been evaluated. The theoretical results of glazed hybrid micro-channel photovoltaic thermal (MCPVT) module for 75 W_p have been compared with the result of single channel photovoltaic thermal (SCPVT) module. The average value of electrical and thermal efficiency of glazed hybrid MCPVT module are 14.7% and 10.8% respectively which is significantly higher than SCPVT module. The overall annual exergy efficiency based on second law of thermodynamics has also been evaluated at different mass flow rate for glazed hybrid MCPVT module for Srinagar climatic condition. It has been observed that maximum overall exergy efficiency is 20.28% at 0.000108 kg/s mass flow rate.     

Measurement of concentrator solar cell efficiency at high concentration and narrow-band spectrum

High efficiency of solar cells may be obtained at high concentration and narrow-band spectrum system. Difficulties are encountered in determination of the cell efficiency using narrow-band-artificial-light sources at high concentration. A method is proposed in this article for determination of the solar cell efficiency at high concentration and narrow-band spectrum. This method is based on measurement of the solar cell fill factor and the open-circuit voltage at moderate concentration and full spectrum, and based on a calculation procedure.     

Effect of hydrogen dilution on intrinsic a-Si:H layer between emitter and Si wafer in silicon heterojunction solar cell

In silicon heterojunction solar cells, a thin intrinsic amorphous-silicon (a-Si:H) buffer layer between a doped emitter and a c-Si wafer is essential to minimize carrier recombination. This study examines the effect of H₂ dilution on the properties of the intrinsic a-Si:H layers deposited on Si wafers by plasma-enhanced chemical vapor deposition. A H₂/SiH₄ ratio of 24 led to improvements in the quality of intrinsic a-Si:H films and in the performance of passivation compared to a-Si:H film without H₂ dilution. A high H₂-dilution ratio, however, degraded the passivation of the a-Si:H film. The Si heterojunction solar cells with an optimal intrinsic a-Si:H layer showed an efficiency of 12.3%.