Synthesis of TiO<Subscript>2</Subscript> nanoparticle using sol–gel route and testing its photovoltaic performance in dye-sensitized solar cell

In the present work, sol–gel method is used to synthesize TiO₂ nanoparticle. The characterization of the prepared TiO₂ powder is done using Powder X-ray diffraction (powder XRD), Scanning Electron Microscope (SEM), Energy-Dispersive X-Ray Spectroscopy (EDS) and Ultraviolet-Visible Spectrophotometry (UV-Vis). The XRD pattern reveals formation of anatase phase TiO₂. The SEM images reveal agglomeration of nanoparticles. The absorbance spectrum of TiO₂ nanoparticles was observed with excitonic peaks at 327 nm and the band gap came out to be ~3.2 eV. This prepared TiO₂ was tested for photovoltaic performance by using it in the Dye sensitized solar cell (FTO/TiO₂/N719/KI-I₂/Pt). Conversion of solar light energy to electricity was successfully done using this TiO₂. The fabricated cell showed an open-circuit voltage (V _OC) of 587 mV and short-circuit current density (J _SC) of 5.06 mA/cm². Maximum power (P _max) generated was 1.912 mW/cm² with a fill factor (FF) of 0.644 and a conversion efficiency of 1.91%.     

Influence of gamma radiation on spectral photosensitivity of (Si<Subscript>2</Subscript>)<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript> (ZnSe)<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> solid solution

Increase of the photosensitivity of the pSi-n(Si₂)_{1 ? x} (ZnSe) _x (0 ≤ x ≤ 0.01) structure exposed to gamma radiation with photon energy E _ph ≥ 2.3 eV has been demonstrated. It is shown that irradiation with dose up to 10⁴ rad raises and radiation with dose up to 10⁵ rad reduces the forward current of the pSi-n(Si₂)_{1 ? x} (ZnSe) _x structure.     

Fabrication and investigation of ultravialet Au-Zn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Cd<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>S-Mo-structures

For the first time fabricated and investigated the photovoltaic characteristics of Au-Zn _x Cd_1–x S-Mofilm structural injection photo detectors sensitive to narrow the ultraviolet region of the electromagnetic spectrum, based on polycrystalline Zn _x Cd_1–x S layers. It was found by adjusting the flow of ZnS and CdS coming to the surface Mo substrate can control the shape of the spectral sensitivity of the Au-Zn _x Cd_1–x S-Mo-film structural injection photo detectors. The results will allow to optimize the structure of photo detectors and solar cells based on polycrystalline thin film solar cells.     

Effect of gamma irradiation on photoconductivity and photosensitivity of Si<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Sn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> solid solutions

The results of studies of the structural feature and the effect of low-dose gamma irradiation (up to 105 rad) on the photoconductivity relaxation and the spectral photosensitivity of pSi-nSi_{1 − x} Sn _x (0 ≤ x ≤ 0.04) structures are described. It is shown that exposure to radiation leads to an increase in the relaxation time constant from 55 to 83 μs and an enhancement in the sensitivity of the structures in the short-wavelength emission spectrum, which is attributed to the radiation-stimulated gettering of crystal lattice defects localized in the near-boundaries regions between Si_{1 −x} Sn _x subcrystallites and Si_{1 − x} Sn _x -Sn and Si_{1 − x} Sn _x -SiO₂ phases.     

The composition dependence of the effective thickness of the base layer in Al<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ga<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>P/GaP heterophotoconverters

The dependence between the composition of Al _x Ga_{1 − x} P heterophotoconverters and the effective thickness of their base layers was established. An empirical formula to estimate the effective thickness of a base layer as a function of the composition of solid-state solution (0 ≤ x ≤ 0.8) was proposed.     

On the possibility of applying <Emphasis Type="Italic">n</Emphasis>/(3C-SiC)–<Emphasis Type="Italic">p</Emphasis>/C<Subscript>DIAMOND</Subscript> white glow heterostructures with improved parameters in illumination systems with power consumption from solar radiation

The voltage-current characteristics and electroluminescence of a light-emitting-diode (LED) n/(3C-SiC)–p/ C_DIAMOND heterostructure with white glow without phosphor created on the basis of diamond film grown by the CVD method on n/(3C-SiC) substrates with a doped level of (5–8) × 10¹⁷ cm^–3 are considered It is shown the possibility to improve the characteristics of created LED structures by their irradiation with a flux of high-energy (5 MeV) electrons of a certain dose and heat treatment.     

Simulation and economic optimization of a solar assisted combined ejector–vapor compression cycle for cooling applications

This paper describes the hourly simulation and optimization of a thermally driven cooling cycle assisted by solar energy. The double stage solar ejector cooling cycle is modelled using the TRNSYS-EES simulation tool and the typical meteorological year file containing the weather data of Florianópolis, Brazil. The first stage is performed by a mechanical compression system with R134a as the working fluid, while the second stage is performed by a thermally driven ejector cycle with R141b. Flat plate collectors and an auxiliary energy burner provide heat to the ejector cycle. The thermo-economical optimization is carried out with respect to the intercooler temperature and the flat plate solar collector area, for given specific costs of the auxiliary energy and electric energy, the capital cost of the collectors, ejector cooler, and the capital cost of equivalent mechanical compression cooler.     

Effects on global CO<Subscript>2</Subscript> emissions when substituting LPG with bio-SNG as fuel in steel industry reheating furnaces—the impact of different perspectives on CO<Subscript>2</Subscript> assessment

The iron and steel industry is the second largest user of energy in the world industrial sector and is currently highly dependent on fossil fuels and electricity. Substituting fossil fuels with renewable energy in the iron and steel industry would make an important contribution to the efforts to reduce emissions of CO₂. However, different approaches to assessing CO₂ emissions from biomass and electricity use generate different results when evaluating how fuel substitution would affect global CO₂ emissions. This study analyses the effects on global CO₂ emissions when substituting liquefied petroleum gas with synthetic natural gas, produced through gasification of wood fuel, as a fuel in reheating furnaces at a scrap-based steel plant. The study shows that the choice of system perspective has a large impact on the results. When wood fuel is considered available for all potential users, a fuel switch would result in reduced global CO₂ emissions. However, applying a perspective where wood fuel is seen as a limited resource and alternative use of wood fuel is considered, a fuel switch could in some cases result in increased global CO₂ emissions. As an example, in one of the scenarios studied, a fuel switch would reduce global CO₂ emissions by 52 ktonnes/year if wood fuel is considered available for all potential users, while seeing wood fuel as a limited resource implies, in the same scenario, increased CO₂ emissions by 70 ktonnes/year. The choice of method for assessing electricity use also affects the results.     

Situation and measures of China’s CO<Subscript>2</Subscript> emission mitigation after the Paris Agreement

Global response to climate change has entered the phase of full implementation of the Paris Agreement. To control the global temperature rise below 2°C, all countries must make more efforts to reduce emission. China has combined its goal of emission reduction for combating climate change with its domestic sustainable development strategy to promote energy revolution and the transition of economic development to low-carbon patterns. Through reinforcing the commitment and action before 2020, the CO₂ intensity of GDP can decrease by more than 50% by 2020 compared with that of 2005, and the external commitment target of a 40%–45% decrease can be over fulfilled. Currently, under the new economic normal, China further strengthens the policy measure, vigorously saves energy, enhances energy use efficiency and the economic output benefit, and simultaneously develops new and renewable energy and accelerates energy structural decarbonization, so that the annual decrease rate of the CO₂ intensity of GDP keeps a high level of more than 4% and remains increasing. Thus, the decrease rate of the CO₂ intensity of GDP will exceed the GDP growth rate, and then CO₂ emission will peak around 2030. This will promote the fundamental turning of economic development mode, and lay a foundation for the establishment of a sustainable energy system with near-zero emissions and with new and renewable energy as the main body in the second half of this century. China implements the concept of green low-carbon development and accelerates the low carbon transition of energy and economy to achieve win-win results in economic growth and CO₂ emission mitigation, and these policies and actions will also provide experiences for many other developing countries. On the other hand, China will continue to play a positive and constructive leading role in the implementation of the Paris Agreement internationally, and promote the construction of new mechanisms of win-win cooperation, fairness and justice and common development for global climate governance. Moreover, China will make an effort to build a community of common destiny for mankind, promote pragmatic cooperation among countries, especially among developing countries, and take combating climate change as a new development opportunity for jointly moving toward climate-friendly low-carbon economic development path.     

Modeling of the absorption phase of a cycle with solar absorption using the couple NH3–H2O for in-sight energy storage

In this work, the emphasis is laid on the study of energy storage and the estimate of the energy density stored for use in the absorption machine in its simplest configuration. As a matter of fact, a simulation program is used to calculate the solution densities and the dynamic system storage in an absorption cycle phase. In times of discharge, the evaporator and the absorber are the only devices in the cycle to operate either in energy or in the upgrading refrigeration. Such a study allows us to select the cooling phase with three storage tanks. At the entrance of the evaporator and the absorber, both reservoirs contain the pure refrigerant and the weak solution already stored in the generation phase during an operating day (charging phase). At the output of the third absorber, the tank is empty. An amount of the refrigerant evaporated at low temperature in the evaporator, receiving an amount of heat Q_E, and is absorbed by the weak solution with the release of an amount of heat Q_A at an intermediate temperature. The rich solution is, then, stored in the third tank. At the end of cooling, when both tanks are empty, the third will be full in order to be used in the generating phase.     

Study of the effect of finned tube adsorber on the performance of solar driven adsorption cooling machine using activated carbon–ammonia pair

Solar refrigeration represents an important application of solar energy due to the excellent matching between the high sunshine and the refrigeration needs. Solar adsorption refrigeration devices are among the significant techniques used to meet the needs for cooling requirements. Several solar refrigeration systems have been proposed and are under development such as sorption systems including liquid/vapor, solid/vapor absorption, adsorption, vapor compression and others. The purpose of this paper is to identify the influence of a cylindrical adsorber on the performances of a solar adsorption refrigerating machine. The adsorber heated by solar energy contains an activated carbon–ammonia pair; it is composed by many cylindrical tubes welded using external fins. A model based on the conservation equations of energy and mass in the adsorber has been developed and well described. Using real solar irradiance data as well as many initial conditions, the model computes for each point and in the considered time interval during the day, the temperature, the adsorbed mass, the pressure inside the adsorber and the solar performance coefficient (COP). The results show that the optimal diameter of the adsorber with fins is greater than the one without fins. Moreover the mass cycled in the case of an adsorber equipped with external fins is more significant than the one without fins, and the maximal temperature reached in the adsorber with fins attains 97 °C while in the adsorber without fins reaches 77 °C. Thus, the performances of the solar adsorption refrigerating machine with an adsorber equipped with fins are higher than the machine without fins.     

Cooling performance investigation of electronics cooling system using Al2O3–H2O nanofluid

In this study, the cooling performance of Al₂O₃–H₂O nanofluid was experimentally investigated as a much better developed alternative for the conventional coolant. For this purpose the nanofluid was passed through the custom-made copper minichannel heat sink which is normally attached with the electronic heat source. The thermal performance of the Al₂O₃–H₂O nanofluid was evaluated at different volume fraction of the nanoparticle as well as at different volume flow rate of the nanofluid. The volume fraction of the nanoparticle varied from 0.05 vol.% to 0.2 vol.% whereas the volume flow rate was increased from 0.50 L/min to 1.25 L/min. The experimental results showed that the nanofluid successfully has minimized the heat sink temperature compared to the conventional coolant. It was noticed also that the thermal entropy generation rate was reduced via using nanofluid instead of the normal water. Among the other functions of the nanofluid are to increase the frictional entropy generation rate and to drop the pressure which are insignificant compared to the normal coolant. Given the improved performance of the nanofluid, especially for high heat transportation capacity and low thermal entropy generation rate, it could be used as a better alternative coolant for the electronic cooling system instead of conventional pure water.     

Comparative study of activity of cerium oxide at thermal reduction temperatures of 1300–1550 °C for solar thermochemical two-step water-splitting cycle

Thermochemical two-step water-splitting using CeO₂ (cerium oxide) particles was studied to examine oxygen and hydrogen productivity and repeatability at thermal reduction (T-R) temperatures of 1300–1550 °C and water decomposition (W-D) temperatures of 400–1000 °C for the production of hydrogen from water using concentrated solar radiation as the energy source. The temperature dependency of oxygen and hydrogen productivity and the cyclic repeatability of CeO₂ are reported in this paper. The characteristic features of CeO₂ particles in the thermochemical two-step water-splitting cycle are compared with the well-known highly active reactive mediums of zirconia-supported Ni-ferrites (NiFe₂O₄/m-ZrO₂ and NiFe₂O₄/c-YSZ) and unsupported NiFe₂O₄.     

Questions of Simplifying the Methods of Testing Photoconverters Based on Cu(In,Ga)Se<Subscript>2</Subscript>. Part 1: A Basis for Mathematical Modeling of the Current–Voltage Characteristics

An analysis of possible errors of laboratory studies of current–voltage (I–V) characteristics for solar cells based on Cu(In,Ga)Se₂ (CIGS) using different lamps is provided, and the possibility of simplifying the procedure of testing the cells and panels by calculations and modeling is presented. Formulas are presented to develop mathematical models of the correlation between the quantum efficiency and the spectrum of the used lamp to obtain (I–V) characteristics of solar cells based on CIGS, which simplifies the testing procedure and data collection.     

Investigation of thermal conductivity and viscosity of Al2O3/water–ethylene glycol mixture nanocoolant for cooling channel of hot-press forming die application

Hot-press forming process is widely used to produce lightweight chassis in automotive industries. The hot-press forming process currently uses water as coolant to quench boron steels in a closed die with a cooling channel. However, to enhance performance of hot-press forming die, the fluid with better thermal properties will be used instead of normal water. This study dispersed Al₂O₃ nanoparticles with an average diameter of 13 nm in three volume percentages base ratios of water (W) to ethylene glycol (EG) (i.e. 60:40, 50:50, and 40:60) by two-step preparation. The two main parameters in cooling rate performance are thermal conductivity and viscosity. The nanocoolant of Al₂O₃/water–ethylene glycol mixture is prepared for the volume concentration range of 0.2 to 1.0%. The thermal conductivity and viscosity are then measured at temperature range of 15 to 55 °C. The highest enhancement of thermal conductivity was observed to be 10% higher than base fluid for 1.0% volume concentration at 55 °C in 60:40 (W/EG). However, the highest enhancement of viscosity was measured to be 39% for 1.0% volume concentration in 40:60 (W/EG) at 25 °C. The convective heat transfer coefficient of 1.0% concentration in 60:40 (W:EG) at 25 °C is enhanced by 25.4% better than that of 50:50 and 40:60 (W:EG) base fluid. Therefore, this study recommends the use of Al₂O₃ in 60:40 (W:EG) mixture with volume concentration of less than 1.0% for application in cooling channel of hot-press forming die. Nanocoolant as cooling agent with higher heat transfer coefficient compared to the base fluid can reduce the cycle time and increase the productivity of hot-press forming process.     

Synthesis and electrochemical properties of lithium cobalt oxides prepared by molten-salt synthesis using the eutectic mixture of LiCl–Li2CO3

Lithium cobalt oxide powders have been successfully prepared by a molten-salt synthesis (MSS) method using a eutectic mixture of LiCl and Li₂CO₃ salts. The physico-chemical properties of the lithium cobalt oxide powders are investigated by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), particle-size analysis and charge–discharge cycling. A lower temperature and a shorter time (∼700°C and 1 h) in the Li:Co=7 system are sufficient to prepare single-phase HT-LiCoO₂ powders by the MSS method, compared with the solid-state reaction method. Charge–discharge tests show that the lithium cobalt oxide prepared at 800°C has an initial discharge capacity as high as 140 mA h g⁻¹, and 100 mA h g⁻¹ after 40 cycles. The dependence of the synthetic conditions of HT-LiCoO₂ on the reaction temperature, time and amount of flux with respect to starting oxides is extensively investigated.     

Is it possible to carry out impact ionization in the narrow energy gap of <Emphasis Type=Italic>p-p,n-n</Emphasis> heterojunctions and increase the efficiency of thin-film solar cells?

We try to justify the idea that it is possible to implement impact ionization and generate additional electron-hole pairs in the narrow energy-gap layer by accelerating the high energy-gap photoelectrons by the field of a p-p, n-n heterojunction barrier and by increasing the efficiency of thin-film solar cells. We investigate whether impact ionization in the GaSb layer of a p-CdTe-p-GaSb heterojunction is possible and whether it is possible to increase the efficiency of a CdTe solar cell up to 50%.     

Properties of tandem-junction heterophotoconverters with GaAs <Emphasis Type="Italic">p–n</Emphasis> junctions under exposure by bilaterally concentrated sunlight

Properties of GaAs/Al_xGa_1–xAs heterophotoconverters fabricated on two sides of monocrystal plates from GaP and GaAs under lighting conditions by V-shaped concentrators are described. It it found that, owing to the increased transparency of the photoconverter structure with respect to thermal photons and comparatively low GaP thermal resistance, the temperature increment of the p–n junctions and relative losses of the electrical power are notably lower than for photoconverters of the same structure on the basis of GaAs.