Semiconductor Solar Cells Research Articles

CONVERTER SOLAR RADIATION INTO ELECTRICITY TO SUPPLY THE AUTOMOTIVE SEMICONDUCTOR THERMOELECTRIC AIR CONDITIONING

The article considers the possibility to increase the efficiency of converters of solar radiation into electricity by combining constructive photoelectric effect, See-beck thermoeffect and semiconductor solar cells, which will create integrated de￾vice to provide power semiconductor thermoelectric automobile air conditioner.

Concentrated Photo Voltaics (CPV): a case study

Concentrated PhotoVoltaic (CPV), among green energy solutions, nowadays has the ambition to reach grid-parity without subside. CPV substitutes large areas of expensive semiconductor solar cells, with concentrating optics made of cheap materials. Moreover the cells that are suitable for CPV exhibits an unprecedented efficiency and their technology is progressing every year. A case study project, TwinFocus® , will be presented in detail.

Upgrading Metallurgical Grade Silicon to Solar Grade Silicon

<p>he photovoltaics (PV) is a method of direct conversion of solar energy to electricity using semicon-ductor solar cells. In terms of globally installed capacity, PV remains third the most important renewable energy source after hydro and wind powers. 31.1 GW of PV systems were installed around the world in 2012 and up from 30.4 GW in 2011.There is a rapid growth of PV cell production and it is expected to increase further. However PV technology have to cost effective in comparison to hydro or wind powers and other sources of renewable energy. It has to reach the “grid parity” i.e. less or equal price for generated electricity <br />power. More than 85% of solar cells (SC) are made from solar grade silicon (SoGSi). SoGSi is produced by purification of metallurgy grade silicon (MGSi) which is produced by carbon recovering silicon from quartz. Also Quartz is an initial and essential material for obtaining SoGSi and SC. Rich resource of quartz <br />Sarykol located at southern part of Kazakhstan where the main factory for MG Si production «Каzsilicon» is situated. Upgrading of MGSi up to SoGSi consists is a number of technological steps and SoGSi is basis for PV industry. Therefore the cost of SoGSi determines the competitiveness of PV technology compared to <br />other energy sources. There are several chemical and metallurgical technologies for SoGSi production. This paper briefly describes these technologies and shows main advantages of metallurgical technologies based on slag refining (oxygenation). Considered technologies are the basis for industrial production of SoGSi, <br />solar cells with an efficiency of 15.8-17.1% and solar panels. The 1st power plant made from solar panels in Kazakhstan was launched in December 25, 2012 by «AstanaSolar» with a total capacity of 250 kW.</p>

ChemInform Abstract: A Brief Survey on Basic Properties of Thin Films for Device Application

AbstractReview: 19 refs.

Device modeling of perovskite solar cells based on structural similarity with thin film inorganic semiconductor solar cells

Device modeling of CH3NH3PbI3−xCl3 perovskite-based solar cells was performed. The perovskite solar cells employ a similar structure with inorganic semiconductor solar cells, such as Cu(In,Ga)Se2, and the exciton in the perovskite is Wannier-type. We, therefore, applied one-dimensional device simulator widely used in the Cu(In,Ga)Se2 solar cells. A high open-circuit voltage of 1.0 V reported experimentally was successfully reproduced in the simulation, and also other solar cell parameters well consistent with real devices were obtained. In addition, the effect of carrier diffusion length of the absorber and interface defect densities at front and back sides and the optimum thickness of the absorber were analyzed. The results revealed that the diffusion length experimentally reported is long enough for high efficiency, and the defect density at the front interface is critical for high efficiency. Also, the optimum absorber thickness well consistent with the thickness range of real devices was derived.

Technical Tasks and Development Current Status of Organic Solar Cells

Serious environmental problems have been caused by the greenhouse effect due to carbon dioxide(CO2) or nitrogen oxides(NOx) generated by the use of fossil fuels, including oil and liquefied natural gas. Many countries, including our own, the United States, those of the European Union and other developed countries around the world; have shown growing interest in clean energy, and have been concentrating on the development of new energy-saving materials and devices. Typical non-fossil-fuel sources include solar cells, wind power, tidal power, nuclear power, and fuel cells. In particular, organic solar cells(OSCs) have relatively low power-conversion efficiency(PCE) in comparison with inorganic(silicon) based solar cells, compound semiconductor solar cells and the CIGS [Cu(In1-xGax)Se2] thin film solar cells. Recently, organic cell efficiencies greater than 10 % have been obtained by means of the development of new organic semiconducting materials, which feature improvements in crystalline properties, as well as in the quantum-dot nano-structure of the active layers. In this paper, a brief overview of solar cells in general is presented. In particular, the current development status of the next-generation OSCs including their operation principle, device-manufacturing processes, and improvements in the PCE are described.

Analyses of Polymer Passivation on the Surface Reflectivity of GaAs/AlGaAs Solar Cell

A traditional III-V GaAs/AlGaAs based semiconductor solar cell heterojunction structure, i.e. n-GaAs/n-AlGaAs/n-GaAs/i-GaAs/p-GaAs is used in this study to investigate the surface polymer passivation on this kind of solar cell. For GaAs/AlGaAs solar cell, the top n-GaAs/n-AlGaAs structure is responsible for the selective etching stop layer. The selective etched surface barriers associated with polymer gratings with different aspect ratios, i.e. grating period (gp) to depth (d), are produced on solar cell surface by using the photolithography and Micro Electro Mechanical Systems (MEMS) techniques. A reflective-type diffraction optical grating is fabricated on the surface of the solar cell to redirect the incident light reflected from the solar cell back onto the solar cell surface. The experimental results show that the addition of the surface optical gratings reduce the light reflectivity value as high as 25%. From inspection of surface reflectivity , the average reflectivity is found to be decreased from 12.1% down to 7.9 %.

A highly efficient hybrid GaAs solar cell based on colloidal-quantum-dot-sensitization.

This paper presents a hybrid design, featuring a traditional GaAs-based solar cell combined with various colloidal quantum dots. This hybrid design effectively boosts photon harvesting at long wavelengths while enhancing the collection of photogenerated carriers in the ultraviolet region. The merits of using highly efficient semiconductor solar cells and colloidal quantum dots were seamlessly combined to increase overall power conversion efficiency. Several photovoltaic parameters, including short-circuit current density, open circuit voltage, and external quantum efficiency, were measured and analyzed to investigate the performance of this hybrid device. Offering antireflective features at long wavelengths and luminescent downshifting for high-energy photons, the quantum dots effectively enhanced overall power conversion efficiency by as high as 24.65% compared with traditional GaAs-based devices. The evolution of weighted reflectance as a function of the dilution factor of QDs was investigated. Further analysis of the quantum efficiency response showed that the luminescent downshifting effect can be as much as 6.6% of the entire enhancement of photogenerated current.

Application of optical spectroscopic techniques in the characterization of elastic strain effects in semiconductor heterostructures and nanostructures and in semiconductor-based thin-film solar cells

Applications of optical spectroscopic techniques in the characterization of elastic strain in semiconductor thin films, heterostructures, and nanostructures, and in semiconductor thin-film solar cells (TFSCs) are presented. Examples of elastic strain characterization by Raman spectroscopy, modulation (PR and ER) spectroscopy, and reflectance anisotropy spectroscopy (RAS) are reviewed. In particular, examples of strain evolution in porous silicon thin films and suspended porous silicon membranes for microsensor device technology by Raman spectroscopy, strain quantification in chalcopyrite semiconductors by photoreflectance (PR) spectroscopy, and strain analysis in chalcopyrite semiconductor-based thin-film solar cells Al/Ni/n-ZnO/i-ZnO/CdS/CIS(CIGS)/Mo/glass by electroreflectance (ER) spectroscopy are discussed. A novel method of highly sensitive detection of strains down to 10−5 by surface-sensitive RAS is introduced. Strain-calibrated RAS spectra of Si and III–V compound semiconductors GaAs and InP are shown to provide a useful tool for ex situ quantification and in situ, during semiconductor growth, control of strain.

Derivation of the open-circuit voltage of organic solar cells

Organic photovoltaic cells have improved in efficiency from 1% two decades ago to over 10% today. Continued improvement necessitates a theoretical understanding of the factors determining efficiency. Organic photovoltaic efficiency can be parameterized in terms of open-circuit voltage, short-circuit current, and fill factor. Here we present a theory that explains the dependencies of open-circuit voltage on semiconductor energy levels, light intensity, solar cell and light-source temperatures, charge-carrier recombination, and external fluorescence efficiency. The present theory also explains why recombination at the donor-acceptor heterointerface is a dominant process in heterojunction-based cells. Furthermore, the Carnot efficiency appears, highlighting the connection to basic thermodynamics. The theory presented here is consistent with and builds on the experimental and theoretical observations already in the literature. Crucially, the present theory can be straightforwardly derived in a line-by-line fashion using standard tools from statistical physics.

Improvement of the physical properties of ZnO/CdTe core-shell nanowire arrays by CdCl2 heat treatment for solar cells.

CdTe is an important compound semiconductor for solar cells, and its use in nanowire-based heterostructures may become a critical requirement, owing to the potential scarcity of tellurium. The effects of the CdCl2 heat treatment are investigated on the physical properties of vertically aligned ZnO/CdTe core-shell nanowire arrays grown by combining chemical bath deposition with close space sublimation. It is found that recrystallization phenomena are induced by the CdCl2 heat treatment in the CdTe shell composed of nanograins: its crystallinity is improved while grain growth and texture randomization occur. The presence of a tellurium crystalline phase that may decorate grain boundaries is also revealed. The CdCl2 heat treatment further favors the chlorine doping of the CdTe shell with the formation of chlorine A-centers and can result in the passivation of grain boundaries. The absorption properties of ZnO/CdTe core-shell nanowire arrays are highly efficient, and more than 80% of the incident light can be absorbed in the spectral range of the solar irradiance. The resulting photovoltaic properties of solar cells made from ZnO/CdTe core-shell nanowire arrays covered with CuSCN/Au back-side contact are also improved after the CdCl2 heat treatment. However, recombination and trap phenomena are expected to operate, and the collection of the holes that are mainly photo-generated in the CdTe shell from the CuSCN/Au back-side contact is presumably identified as the main critical point in these solar cells.

Pulse plating of semiconductors for solar cells

Parameters of rectangular potential pulse electrodeposition which have allowed the obtaining of near-stoichiometric copper indium diselenide layers were determined by means of energy-dispersive X-ray spectroscopy, scanning electron microscopy and the film resistivity measurements. Studies of effects of the pulse electrodeposition modes on structural and substructural parameters, morphology and optical properties of zinc oxide arrays allowed creation of hierarchical nanostructures with large specific surface areas suitable for dye-sensitized solar cells and organic photovoltaic devices. Optimization of pulse electrodeposition modes by means X-ray diffractometry, optical spectrophotometry and atomic force microscopy allowed adjusting sizes of parabolic nipples for creating antireflective moth-eye structure suitable for use in photovoltaic devices.

Photoactive Electrodes Incorporating Electrosprayed Bacterial Reaction Centers

Highly efficient light absorption and charge separation within the photosystem and reaction center (RC) complexes of photosynthetic plants and bacteria are of great interest for solar cell and photo detector applications, since they offer almost unity quantum yield and expected ultimate power conversion efficiencies of more than 18% and 12%, respectively. In addition, the charge separated states created by these protein complexes are very long lived compared to conventional semiconductor solar cells. In this work, a novel technique is presented for the deposition of photosynthetic protein complexes, by electrospraying RCs of Rhodobacter sphaeroides onto highly ordered pyrolytic graphite (HOPG) electrodes. Remarkably, it is shown that the RCs not only survive exposure to the high electric fields but also yield peak photocurrent densities of up to 7 μA cm−2, which is equal to the highest value reported to date.

Simulation of Rough Surface of CIGS (CuInGaSe) Solar Cell by RCWA (Rigorous Coupled Wave Analysis) Considering the Incoherency of Light

The surface of semiconductor solar cells, such as a-Si or CIGS (CuInGaSe) solar cells is not flat but textured in the microscopic domain. With textured surfaces, the optical reflectivity of a solar cell is different from that of flat surfaces in the wavelength region. In this paper, the effects of a textured surface on a CIGS solar cell are presented by RCWA (Rigorous Coupled Wave Analysis) method. The effect of incoherent light is also considered by RCWA with a Fourier analysis while conventional optical simulation uses the input light on the solar cell as coherent light. Using experimental results, the author showed that the RCWA method with a Fourier analysis is a proper method to simulate the optical properties of CIGS solar cells.

Ruthenium(ii) multi carboxylic acid complexes: chemistry and application in dye sensitized solar cells

Novel ruthenium multi carboxylic complexes (RMCCs) have been synthesized by using ruthenium nitrosyl nitrate, 1,2,4,5-benzenetetracarboxylic acid (H4btec) and 4,7-diphenyl-1,10-phenanthroline (BPhen) as photosensitizers for titanium dioxide semiconductor solar cells. The complexes were characterized by (1)H-NMR, FT-IR, UV-Vis, ICP and CHN analyses. The reaction details and features were then described. SEM analysis revealed that the penetration of dyes into the pores of the nanocrystalline TiO2 surface was improved by increasing the number of btec units. The solar energy to electricity conversion efficiency of complexes shows that the number of attached carboxylates on a dye has an influence on the photoelectrochemical properties of the dye-sensitized electrode. An incident photon-to-current conversion efficiency (IPCE) of 13% at 510 nm was obtained for ruthenium complexes with three btec units.

Improved Light Harvesting in N719 Sensitized Nanocrystalline TiO2 Solar Cells with Coumarin 6 Dye

Dye-sensitized solar cells (DSSCs) are a promising alternative to conventional semiconductor solar cells due to their ease of fabrication and low manufacturing cost. Ru-based dyes, particularly N719, are the typical dye for DSSC applications. However, N719-based DSSCs have weak absorbance at a wavelength around 440nm. In this work, we aimed to improve light absorption of the N719-based DSSCs by adding a luminescent dye, Coumarin 6 (C6), into an electrolyte. C6 dye were chosen as it has an absoption and luminescence spectrum complementary to that of N719. The absorption and luminescence spectra of the C6 solution with different dye concentrations, ranging from 1 – 25 M, were investigated in order to find the optimum concentration that is suitbale for the DSSC applications. Moreover, N719 based DSSCs with and without C6 added were fabricated and experimentaly compared. The measurement results show that the N719-based DSSC with C6 dye has the improvement in both short circuit current and device efficiency.

Red electroluminescence of ruthenium sensitizer functionalized by sulfonate anchoring groups.

We have synthesized five novel Ru(ii) phenanthroline complexes with an additional aryl sulfonate ligating substituent at the 5-position [Ru(L)(bpy)2](BF4)2 (1), [Ru(L)(bpy)(SCN)2] (2), [Ru(L)3](BF4)2 (3), [Ru(L)2(bpy)](BF4)2 (4) and [Ru(L)(BPhen)(SCN)2] (5) (where L = 6-one-[1,10]phenanthroline-5-ylamino)-3-hydroxynaphthalene 1-sulfonic, bpy = 2,2'-bipyridine, BPhen = 4,7-diphenyl-1,10-phenanthroline), as both photosensitizers for oxide semiconductor solar cells (DSSCs) and light emitting diodes (LEDs). The absorption and emission maxima of these complexes red shifted upon extending the conjugation of the phenanthroline ligand. Ru phenanthroline complexes exhibit broad metal to ligand charge transfer-centered electroluminescence (EL) with a maximum near 580 nm. Our results indicated that a particular structure (2) can be considered as both DSSC and OLED devices. The efficiency of the LED performance can be tuned by using a range of ligands. Device (2) has a luminance of 550 cd m(-2) and maximum efficiency of 0.9 cd A(-1) at 18 V, which are the highest values among the five devices. The turn-on voltage of this device is approximately 5 V. The role of auxiliary ligands in the photophysical properties of Ru complexes was investigated by DFT calculation. We have also studied photovoltaic properties of dye-sensitized nanocrystalline semiconductor solar cells based on Ru phenanthroline complexes and an iodine redox electrolyte. A solar energy to electricity conversion efficiency (η) of 0.67% was obtained for Ru complex (2) under standard AM 1.5 irradiation with a short-circuit photocurrent density (Jsc) of 2.46 mA cm(-2), an open-circuit photovoltage (Voc) of 0.6 V, and a fill factor (ff) of 40%, which are all among the highest values for ruthenium sulfonated anchoring groups reported so far. Monochromatic incident photon to current conversion efficiency was 23% at 475 nm. Photovoltaic studies clearly indicated dyes with two SCN substituents yielded a higher Jsc for the cell than dyes with a tris-homoleptic anchor substituent.

ChemInform Abstract: Fullerene‐Bisadduct Acceptors for Polymer Solar Cells

AbstractReview: 67 refs.

Influence of annealing conditions on the crystallographic structure, chemical composition and luminescence of ZnO thin films

ZnO thin films have many applications in semiconductor devices, such as semiconductor lasers, amplifiers, solar cells, chemical and ultraviolet sensors. We produced ZnO thin films on Si (400) substrates, using e-beam technique and subsequently annealed them under different conditions (i.e., temperature (200–800), time (60min and 180min) and environment (air and oxygen flow). The ZnO (002) preferred orientation which increases in intensity with annealing temperature and annealing time is deduced from X-ray diffraction (XRD) results. Dislocation density was higher for the films annealed in air which may be caused by the impurities (nitrogen and other species in the air) embedded in the film structure. No significant change in the nano-strain of each group of the samples (annealed under different conditions) was observed. The FESEM images showed a granular structure for annealed samples at 200°C and 800°C and a mixed structure of nanowires and nanosheets for samples annealed at 350°C and 500°C. Two peaks of UV emission and green emission were observed in the photoluminescence (PL) spectra of the produced samples. The UV emission increased with annealing temperature and annealing time showing higher crystal quality while the behavior of the green emission was opposite to that of the UV emission. The ZnO films resulted from annealing in the air showed stronger green emission than those annealed with flow of oxygen indicating higher impurity concentration and oxygen vacancies in the sample.

Enhanced Solar Cell Conversion Efficiency Using Birefringent Liquid Crystal Polymer Homeotropic Films from Reactive Mesogens

Novel birefringent liquid crystal polymer homeotropic films have been coated on semiconductor solar cells to improve the effective incident sunlight angles. The liquid crystal polymer precursor, based on reactive mesogens, is fluidic and flows like liquid. It would distribute uniformly on the solar cell sample surface by any traditional coating technique. The birefringence for light, due to the liquid crystal retardation properties, manipulated the optical length and the deflection of incident light, thus allowed an increase in the energy conversion efficiency. The expensive sunlight tracking systems could be avoided. The processing parameters can be tuned such as different mesogen concentrations and plate speeds of spin-coating. The results showed that the solar cell conversion efficiency was improved from 14.56% to 14.85% at an incident sunlight angle of 15°. It was further improved from 13.40% to 13.81% when the angle was 30°. The interesting angular dependency on solar cell efficiency enhancement has been evaluated.