Maximum Solar Energy Conversion Efficiency Research Articles

High‐Temperature Semiconductor CuO/SiC‐Based Catalyst for Artificial Photosynthesis

AbstractArtificial photosynthesis can convert CO2 and H2O into hydrocarbons via solar energy. However, the extremely low process efficiency is a major obstacle to this application. The photocatalyst is considered to be the key factor to raise the overall solar energy conversion efficiency. Much research focused on co‐catalysts, but less attention has been paid on the high‐temperature semiconductor. Herein, a strategy is proposed involving high‐temperature semiconductor to design target photocatalyst dealing with the artificial photosynthesis at high temperature. Based upon this strategy, a CuO/SiC catalyst with single atom characteristic was designed, prepared and the activity of CO2 photoreduction with H2O was tested in a high temperature environment. Above 150 °C, the catalyst activity was boosted and unprecedented performance values were attained. Under the irradiation condition delivered by a 1000 W Xe light and at 350 °C, the obtained yields of CH4, C2H4, and C2H6 were 2041.4 μmol ⋅ g−1, 15.2 μmol ⋅ g−1, and 63.6 μmol ⋅ g−1, respectively. The overall CO2 conversion reached 24.6 % and the maximum solar energy conversion efficiency was 2.3 % without any sacrificed agents. This strategy will be helpful to overcome the current limitations for the industrialization of artificial photosynthesis and accelerate the related research on photothermal catalysis.

Potential of aldehyde bearing N,N-diphenylhydrazone based organic dye in TiO2, ZnO and TiO2/ZnO bilayer semiconductor constituting dye sensitized solar cells

Organic chromophore based on N,N-diphenylhydrazone bearing aldehyde functional group was synthesized and characterized. TiO2 and synthesized ZnO nanorod based semiconducting materials were utilized for preparing working electrodes in dye sensitized solar cells (DSSCs). The prepared ZnO nanorods were analysed by x-ray diffraction, scanning electron microscopy and transmission emission microscopy. DSSCs were fabricated by using TiO2, ZnO and bilayer of TiO2/ZnO coated electrodes. Atomic force microscopic studies were performed for the semiconductor thin films to evaluate the roughness parameters. Maximum solar energy conversion efficiency of 0.062% was acquired from TiO2 based DSSC. ZnO based DSSC shows a lesser efficiency of 0.027%. DSSC fabricated with bilayer electrode shows highest open-circuit potential of 586 mV.

Effect of Preparation Methods on the Tensile, Morphology and Solar Energy Conversion Efficiency of RGO/PMMA Nanocomposites.

In this study, reduced graphene oxide (RGO)/polymethyl methacrylate (PMMA) nanocomposites were prepared by employing in situ polymerization and solution blending methods. In terms of mechanical properties, RGO loading increased the Young’s modulus but decreased the elongation at break for RGO/PMMA nanocomposites. Tensile strength for solution blended RGO/PMMA nanocomposites increased after adding 0.5 wt % RGO, which was attributed to the good dispersion of RGO in the nanocomposites as evidenced from SEM and TEM. Solar energy conversion efficiency measurement results showed that the optimum concentration of RGO in the RGO/PMMA nanocomposites was found to be 1.0 wt % in order to achieve the maximum solar energy conversion efficiency of 25%. In the present study, the solution blended nanocomposites exhibited better overall properties than in situ polymerized nanocomposites owing to the better dispersion of RGO in solution blending. These findings would contribute to future work in search of higher conversion efficiency using nanocomposites.

Electro‐Optics of Colloidal Quantum Dot Solids for Thin‐Film Solar Cells

The electro‐optics of thin‐film stacks within photovoltaic devices plays a critical role for the exciton and charge generation and therefore the photovoltaic performance. The complex refractive indexes of each layer in heterojunction colloidal quantum dot (CQD) solar cells are measured and the optical electric field is simulated using the transfer matrix formalism. The exciton generation rate and the photocurrent density as a function of the quantum dot solid thickness are calculated and the results from the simulations are found to agree well with the experimentally determined results. It can therefore be concluded that a quantum dot solid may be modeled with this approach, which is of general interest for this type of materials. Optimization of the CQD solar cell is performed by using the optical simulations and a maximum solar energy conversion efficiency of 6.5% is reached for a CQD solid thickness of 300 nm.

POWER SUPPLY EFFICIENCY INCREASE FROM COMBINE SOLAR COLLECTOR

The high standards for the power supply leads to the fact that the task of saving energy resources becomes the state priority. In order to increase the efficiency and sustainability of modern cities and various industrial centers, people use of renewable energy sources, which have the required capabilities, in particular solar power engineering. The researches of various types of solar units have to solve the task of maximum solar energy conversion efficiency in the necessary form. The authors of this paper develop the scheme of complex energy delivery to isolated objects from a solar collector. The peculiarity is the use of heating pumps which increase year-round efficiency of combine solar collector usage.

The generalized Shockley-Queisser limit for nanostructured solar cells.

The Shockley-Queisser limit describes the maximum solar energy conversion efficiency achievable for a particular material and is the standard by which new photovoltaic technologies are compared. This limit is based on the principle of detailed balance, which equates the photon flux into a device to the particle flux (photons or electrons) out of that device. Nanostructured solar cells represent a novel class of photovoltaic devices, and questions have been raised about whether or not they can exceed the Shockley-Queisser limit. Here we show that single-junction nanostructured solar cells have a theoretical maximum efficiency of ∼42% under AM 1.5 solar illumination. While this exceeds the efficiency of a non-concentrating planar device, it does not exceed the Shockley-Queisser limit for a planar device with optical concentration. We consider the effect of diffuse illumination and find that with optical concentration from the nanostructures of only × 1,000, an efficiency of 35.5% is achievable even with 25% diffuse illumination. We conclude that nanostructured solar cells offer an important route towards higher efficiency photovoltaic devices through a built-in optical concentration.

Facile one-pot controlled synthesis of Sn and C codoped single crystal TiO2 nanowire arrays for highly efficient photoelectrochemical water splitting

Here we report a (Sn, C) cation–anion codoped single crystal TiO2 nanowire (NW) arrays as a highly efficient solar water splitting photoelectrode, able to be fabricated using a facile one pot hydrothermal synthesis method. The synergetic effects of codoping on the photoelectrochemical activity of the photoanode were investigated and compared to undoped and monodoped photoelectrodes. The (Sn, C) codoped TiO2 NW photoanode generated the highest saturated photocurrent density i.e. 2.8mA/cm2 at 1.23V vs RHE while yielding a maximum solar energy conversion efficiency of 1.32% at a potential of 0.55V vs RHE – representing 60%, 94%, and 100% efficiency improvements compared to undoped, Sn doped, and C doped TiO2 NW respectively at same potential. This improvement is attributed to the synergetic effects of Sn and C codopants to lower recombination and enhance life time of photogenerated charge-separated carriers on the surface states that lead to efficient hole transfer at the photoelectrode/electrolyte interface. In addition, an increased charge carrier density and conductivity (as evidenced from electrochemical impedance spectroscopy) and the enhanced incorporation of dopants in the codoped system, compared to monodoped system as quantified by XPS, highlights the importance of codoping. The nanomaterial was characterized by XRD, TEM, SEM and Raman UV–vis measurements. This study will guide improvements in the efficiency of TiO2 for PEC water splitting using optimized codopant pairs.

Fabrication of highly ordered Ta2O5 and Ta3N5 nanorod arrays by nanoimprinting and through-mask anodization

Using highly ordered porous anodic alumina membrane fabricated with the aid of nanoimprinting as a mask, Ta2O5 nanorod array with uniform diameter, length, and distribution is grown in situ on a Ta substrate by through-mask anodization. The Ta2O5 nanorod array is further transformed into Ta3N5 nanorod array without damaging the nanorod structure by nitridation. Solar-driven photoelectrochemical water splitting with a maximum solar energy conversion efficiency of 0.36% is demonstrated with the Ta3N5 nanorod array after modifying the surface with cobalt-phosphate as a co-catalyst. The Ta2O5 and Ta3N5 nanorod arrays have potential applications in catalysis, photonics, UV photodetection and solar energy conversion.

Cobalt phosphate-modified barium-doped tantalum nitride nanorod photoanode with 1.5% solar energy conversion efficiency

Spurred by the decreased availability of fossil fuels and global warming, the idea of converting solar energy into clean fuels has been widely recognized. Hydrogen produced by photoelectrochemical water splitting using sunlight could provide a carbon dioxide lean fuel as an alternative to fossil fuels. A major challenge in photoelectrochemical water splitting is to develop an efficient photoanode that can stably oxidize water into oxygen. Here we report an efficient and stable photoanode that couples an active barium-doped tantalum nitride nanostructure with a stable cobalt phosphate co-catalyst. The effect of barium doping on the photoelectrochemical activity of the photoanode is investigated. The photoanode yields a maximum solar energy conversion efficiency of 1.5%, which is more than three times higher than that of state-of-the-art single-photon photoanodes. Further, stoichiometric oxygen and hydrogen are stably produced on the photoanode and the counter electrode with Faraday efficiency of almost unity for 100 min.

Efficiency Limit of Molecular Solar Thermal Energy Collecting Devices

As a larger fraction of energy is based on solar energy and other renewable energy sources, technologies for energy storage and conversion is becoming increasingly important. Molecular solar thermal (MOST) is a concept for long-term storage of solar energy in molecules and release of the energy as heat with full regeneration of the initial materials. The process is inherently closed cycle and emission free. No assessment of the fundamental efficiency limits of the technology has been made. In this report, efficiency limits and fundamental factors for molecular design of molecular solar thermal systems are discussed. Maximum efficiencies and potential temperature gradients are estimated using a number of basic assumptions on desired storage lifetimes and energy losses. The predicted maximum solar energy conversion efficiency is 10.6% at a S1–S0 gap of 1.89 eV. At this S1–S0 gap, the stored energy is able to create temperature differences of ∼300 °C. Several existing systems have an energy storage density i...

(Invited) III-V/GaP Epitaxy on Si for Advanced Photovoltaics and Green Light Emitters

Epitaxy of III-V compound semiconductors on Si-based substrates with lattice constants between Si and Ge is of great interest for photovoltaic applications as it opens a pathway for achieving near ideal bandgap profiles for maximum solar energy conversion efficiency while simultaneously providing a low-cost Si production platform for III-V cell technologies. The same range of lattice constants also enables access to direct gap III-Vs that can fill the "green gap" present in light emitting devices. This presentation focuses on the materials and III-V/Si heteroepitaxy issues that are currently being addressed, which can lead to breakthrough technologies for both photovoltaics and light emitting devices. We focus on an approach in which the grading between Si and Ge (GaAs) is achieved via wider bandgap GaAsyP1-y metamorphic buffers, from GaP to GaAs, enabling access to the underlying Si as an active solar cell component.

Experimental and Numerical Analyses of a Pressurized Air Receiver for Solar-Driven Gas Turbines

A high-temperature pressurized air-based receiver for power generation via solar-driven gas turbines is experimentally examined and numerically modeled. It consists of an annular reticulate porous ceramic (RPC) foam concentric with an inner cylindrical cavity-receiver exposed to concentrated solar radiation. Absorbed heat is transferred by combined conduction, radiation, and convection to the pressurized air flowing across the RPC. The governing steady-state mass, momentum, and energy conservation equations are formulated and solved numerically by coupled finite volume and Monte Carlo techniques. Validation is accomplished with experimental results using a 3 kW solar receiver prototype subjected to average solar radiative fluxes at the CPC outlet in the range 1870–4360 kW m−2. Experimentation was carried out with air and helium as working fluids, heated from ambient temperature up to 1335 K at an absolute operating pressure of 5 bars. The validated model is then applied to optimize the receiver design for maximum solar energy conversion efficiency and to analyze the thermal performance of 100 kW and 1 MW scaled-up versions of the solar receiver.

Maximizing the solar to H 2 energy conversion efficiency of outdoor photobioreactors using mixed cultures

A numerical study is presented aiming to maximize the solar to hydrogen energy conversion efficiency of a mixed culture containing microorganisms with different radiation characteristics. The green algae Chlamydomonas reinhardtii CC125 and the purple non-sulfur bacteria Rhodobacter sphearoides ATCC 49419 are chosen for illustration purposes. The previously measured radiation characteristics of each microorganism are used as input parameters in the radiative transport equation for calculating the local spectral incident radiation within a flat panel photobioreactor. The specific hydrogen production rate for each microorganism as a function of the available incident radiation is recovered from data reported in the literature. The results show that for mono-cultures, the solar to H 2 energy conversion efficiency, for all combinations of microorganism concentrations and photobioreactor thicknesses, fall on a single line with respect to the optical thickness of the system. The maximum solar energy conversion efficiency of mono-cultures of C. reinhardtii and R. spaheroides are 0.061 and 0.054%, respectively, corresponding to optical thicknesses of 200 and 16, respectively. Using mixed cultures, a total conversion efficiency of about 0.075% can be achieved corresponding to an increase of about 23% with respect to that of a mono-culture of C. reinhardtii. It has been shown that the choice of microorganism concentrations for maximum solar energy conversion efficiency in mixed cultures is non-trivial and requires careful radiation transfer analysis coupled with H 2 production kinetics taking into account the photobioreactor thickness.

Highly efficient dye-sensitized solar cells of thick mesoporous titania films derived fromsupramolecular templating

Thick titania films of highly ordered orthorhombic pore organization and sufficient thicknessup to a few micrometers have been synthesized via a supramolecular templated route andlayer-by-layer deposition. An appropriate pre-heat treatment was applied to improve themesopore accessibility. The mesoporous films were highly crystallized with the crystallite size of∼12 nm regardless of the film thickness, due to the spatial confinement of mesopores. Ahigh optical transparency was demonstrated for the mesoporous films, which isascribed to the high mesoporosity and uniformity of the ordered film structure.Both the mesopore accessibility and optical transparency have contributed to thehigh performance of these films as photoanodes in the dye-sensitized solar cells,showing a maximum solar energy conversion efficiency of 6.02% for a film of 5.08 µm in thickness.

Improved model for solar cells with up-conversion of low-energy photons

In this paper we analyze the system proposed by Trupke T, Green MA, Würfel P. [Improving solar cell efficiencies by up-conversion of sub-band-gap light. J Appl Phys 2002; 92: 4117–22] to increase solar cells efficiency. The system consists in adding to the cell a so-called up-converter, which is a device able to convert the low-energy (sub-band gap) incident solar photons into photons of higher energy. The main novelty of the present model consists in taking into account appropriately the refractive index of solar cell and converter materials. Two configurations are studied: cell and rear converter (C–RC) and front converter and cell (FC–C), respectively. The main conclusions of this work are as follows: (1) The maximum solar energy conversion efficiency increases in case of the C–RC system as compared to the efficiency of a solar cell operating alone, especially at higher values of the concentration ratio; (2) the solar energy conversion efficiency of the C–RC system increases by increasing both the cell and the up-converter refractive indices; (3) the energy conversion efficiency does not increase by adding a front up-converter to the cell, whatever the value of the concentration ratio is.

Photoelectrochemical properties of undoped and Ti-doped WO 3

Undoped and Ti-doped WO 3 (up to 0.65 at% Ti) polycrystalline specimens were investigated. The flat band potential was determined based on the photocurrent experiments; the effect of Ti concentration on solar energy conversion efficiency was discussed. It was found that incorporation of titanium ions into WO 3 lattice leads to the decrease of the recombination process and shifts the flat band potential towards positive values. The incident photon-to-current efficiency (IPCE) assumes highest values for WO 3+0.4 at% Ti. The maximum solar energy conversion efficiency has been observed at voltage bias 0.45–0.65 V.

Effect of cyanide on the photo-electrochemical response of n-CdSe/Fe(CN)4−/3−6 electrolytic cell

PHOTOELECTROCHEMICAL cells based on cadmium chalco-genide electrodes in an aqueous ferrocyanide electrolyte1–9 provide a model system for studying the fundamental processes associated with photo-induced interfacial charge transfer, and also hold the promise of converting solar energy to electricity and useful chemical products with high efficiency. Licht9 has suggested that it is possible to devise n-CdSe/[Fe(CN)3−/4−6]aq cells with a maximum solar-energy conversion efficiency of 16.4%, which derives from an open-circuit photovoltage of ∼1.2 V, a value that approaches the thermodynamic limiting value for a semiconductor with a bandgap of 1.7 eV. Licht suggested that improvements in energy conversion efficiency are possible by modifying the electrolyte so as to prevent chemical modification of the semiconductor surface while optimizing the equilibrium concentrations of critical solution species. Here we report that addition of KCN to a ferro/ferricyanide electrolyte does not prevent surface modification on either the (11&2macr;0) face of n-CdX (where X is S or Se) or the (0001) face of n-CdS. We show instead that the current-voltage response observed by Licht is due to a hidden negative ΔG in the system associated with the thermodynamically 'downhill' oxidation of CN−, which accounts for as much as 700 mV of the reported 'open circuit' photovoltage.