Showing papers in "Progress in Photovoltaics in 2010"
439 citations
TL;DR: The current status and future perspectives of CIGS solar cells and modules are discussed in this paper, and the current status, problems, and prospects of co-evaporation and selenization are discussed.
Abstract: The current status and future perspectives of Cu(In1−xGax)Se2 (CIGS) solar cells and modules will be discussed in this paper. The conversion efficiencies of the state of the art laboratory-scale CIGS solar cells exceeded 20%, which are comparable to those of crystalline Si solar cells. The requirements on the properties of CIGS absorbers to achieve such high efficiencies will be described. The CIGS modules are already commercially available based on two major CIGS deposition techniques such as co-evaporation and selenization. The current status, problems, and prospects of co-evaporation and selenization will also be discussed. High-efficiency flexible CIGS solar cells with efficiencies similar to those fabricated on soda–lime glass (SLG) substrates have been achieved by developing a novel Na incorporation technique. Critical issues to demonstrate high-efficiency flexible solar cells will also be discussed. Copyright © 2010 John Wiley & Sons, Ltd.
388 citations
TL;DR: In this paper, a review on the recent work concerning Cd-free buffer and window layers in chalcopyrite solar cells using various deposition techniques as well as their adaptation to chal copyrite-type absorbers such as Cu(In,Ga)Se-2, CuInS2, or Cu(in,Ga)(S,Se)(2).
Abstract: The aim of the present contribution is to give a review on the recent work concerning Cd-free buffer and window layers in chalcopyrite solar cells using various deposition techniques as well as on their adaptation to chalcopyrite-type absorbers such as Cu(In,Ga)Se-2, CuInS2, or Cu(In,Ga)(S,Se)(2). The corresponding solar-cell performances, the expected technological problems, and current attempts for their commercialization will be discussed. The most important deposition techniques developed in this paper are chemical bath deposition, atomic layer deposition, ILGAR deposition, evaporation, and spray deposition. These deposition methods were employed essentially for buffers based on the following three materials: In2S3, ZnS, Zn1-xMgxO.
349 citations
TL;DR: In this article, a wide range of non-vacuum techniques have been used to deposit CIGS thin films, highlighting the state of the art and efforts towards commercialization.
Abstract: Polycrystalline thin films of copper indium diselenide and its alloys with gallium and sulphur (CIGS) have proven to be suitable for use as absorbers in high-efficiency solar cells. Record efficiency devices of 20% power conversion efficiency have been produced by co-evaporation of the elements under high vacuum. However, non-vacuum methods for absorber deposition promise significantly lower capital expenditure and reduced materials costs, and have been used to produce devices with efficiencies of up to 14%. Such efficiencies are already high enough for commercial up-scaling to be considered and several companies are now trying to develop products based on non-vacuum deposited CIGS absorbers. This article will review the wide range of non-vacuum techniques that have been used to deposit CIGS thin films, highlighting the state of the art and efforts towards commercialization.
321 citations
255 citations
TL;DR: In this paper, the authors summarize the progress made recently in understanding the electronic structure of chalcopyrite solar cells and summarize the results of optoelectronic defect spectroscopy.
Abstract: We summarize the progress made recently in understanding the electronic structure of chalcopyrites. New insights into the dispersion of valence and conduction band allow conclusions on the effective masses of charge carriers and their orientation dependence, which influences the transport in solar cell absorbers of different orientation. Native point defects are responsible for the doping and thus the band bending in solar cells. Results of optoelectronic defect spectroscopy are reviewed. Native defects are also the source for a number of metastabilities, which strongly affect the efficiency of solar cells. Recent theoretical findings relate these effects to the Se vacancy and the InCu antisite defect. Experimentally determined activation energies support these models. Absorbers in chalcopyrite solar cells are polycrystalline, which is only possible because of the benign character of the grain boundaries. This can be related to an unusual electronic structure of the GB. Copyright © 2010 John Wiley & Sons, Ltd.
241 citations
TL;DR: In this paper, the authors present a life cycle analysis of the laboratory production of a typical bulk heterojunction organic solar cell and compare this result with those obtained for the industrial production of other photovoltaic technologies.
Abstract: Organic solar cells, both in the hybrid dye sensitized technology and in the full organic polymeric technology, are a promising alternative that could supply solar electricity at a cost much lower than other more conventional inorganic photovoltaic technologies. This paper presents a life cycle analysis of the laboratory production of a typical bulk heterojunction organic solar cell and compares this result with those obtained for the industrial production of other photovoltaic technologies. Also a detailed material inventory from raw materials to final photovoltaic module is presented, allowing us to identify potential bottlenecks in a future supply chain for a large industrial output. Even at this initial stage of laboratory production, the energy payback time and CO2 emission factor for the organic photovoltaic technology is of the same order of other inorganic photovoltaic technologies, demonstrating that there is plenty of room for improvement if the fabrication procedure is optimized and scaled up to an industrial process. Copyright © 2010 John Wiley & Sons, Ltd.
165 citations
TL;DR: In this article, a moth-eye antireflection scheme for silicon solar cells is simulated using rigorous coupled wave analysis and compared to traditional thin film coatings, which outperforms an optimized double layer thin film coating by approximately 2% for the laboratory cell and approximately 3% for encapsulated cell.
Abstract: Nanostructured moth-eye antireflection schemes for silicon solar cells are simulated using rigorous coupled wave analysis and compared to traditional thin film coatings. The design of the moth-eye arrays is optimized for application to a laboratory cell (air–silicon interface) and an encapsulated cell (EVA-silicon interface), and the optimization accounts for the solar spectrum incident on the silicon interface in both cells, and the spectral response of both types of cell. The optimized moth-eye designs are predicted to outperform an optimized double layer thin film coating by approximately 2% for the laboratory cell and approximately 3% for the encapsulated cell. The predicted performance of the silicon moth-eye under encapsulation is particularly remarkable as it exhibits losses of only 0.6% compared to an ideal AR surface
156 citations
TL;DR: In this paper, the authors present experimental results for photocurrent enhancements in thin c-Si solar cells due to light-trapping by self-assembled, random Ag nanoparticle arrays.
Abstract: We present experimental results for photocurrent enhancements in thin c-Si solar cells due to light-trapping by self-assembled, random Ag nanoparticle arrays. The experimental geometry is chosen to maximise the enhancement provided by employing previously reported design considerations for plasmonic light-trapping. The particles are located on the rear of the cells, decoupling light-trapping and anti-reflection effects, and the scattering resonances of the particles are red-shifted to target spectral regions which are poorly absorbed in Si, by over-coating with TiO2. We report a relative increase in photocurrent of 10% for 22 µm Si cells due to light-trapping. Incorporation of a detached mirror behind the nanoparticles increases the photocurrent enhancement to 13% and improves the external quantum efficiency by a factor of 5.6 for weakly absorbed light.
134 citations
TL;DR: BIPV (Building Integrated Photovoltaics) is a multifunctional technology that unifies the photovoltaic module with the overall building outer surface providing the building with several new functions while producing a portion or total building electricity usage as mentioned in this paper.
Abstract: BIPV (Building Integrated Photovoltaics) is a multifunctional technology that unifies the photovoltaic module with the overall building outer surface providing the building with several new functions while producing a portion or total building electricity usage. Increasing the aesthetic, functional and environmental value of a building at a much lower cost than in the recent past, new PV technologies will soon originate a market growth as intense as the growth of traditional PV market has been in the last 5 years. Copyright © 2009 John Wiley & Sons, Ltd.
129 citations
TL;DR: In this paper, a fixed-abrasive wire where diamond grit is fixed onto a bare wire by resin bonding was developed for slicing crystalline silicon ingots, and polycrystalline silicon solar cells have been fabricated for the first time utilizing the wafers sliced with the fixed abrasive wires.
Abstract: For slicing crystalline silicon ingots, we have developed a novel fixed-abrasive wire where diamond grit is fixed onto a bare wire by resin bonding. The properties of the wafers sliced using a multi-wire saw with the fixed-abrasive wire have been investigated. When compared with the wafers sliced with the loose-abrasive wire, the slicing speed is improved by approximately 2.5-fold and the thicknesses of saw-damage layers are reduced by more than a factor of two. Polycrystalline silicon solar cells have been fabricated for the first time utilizing the wafers sliced with the fixed-abrasive wire, and the cells with the saw-damage etching depth of 7 µm have shown photovoltaic properties comparable to those prepared using the wafers sliced with the loose-abrasive wire and subsequently etched to remove the damage layers up to 15 µm. It has been clarified that wafer slicing using the fixed-abrasive wire is promising as a next-generation slicing technique for fabrication of solar cells, particularly thin silicon cells where the wafer thicknesses approach or become less than 150 µm. Copyright © 2010 John Wiley & Sons, Ltd.
TL;DR: In this paper, the epitaxial lift-off (ELO) technique was used to separate a III-V solar cell structure from its underlying GaAs or Ge substrate, and 2-inch GaAs wafer reuse was demonstrated without degradation in performance of subsequent thin-film GaAs solar cells that were retrieved from it.
Abstract: The epitaxial lift-off (ELO) technique can be used to separate a III-V solar cell structure from its underlying GaAs or Ge substrate. ELO from 4-inch Ge wafers is shown and 2-inch GaAs wafer reuse after lift-off is demonstrated without degradation in performance of the subsequent thin-film GaAs solar cells that were retrieved from it. Since a basic wet chemical smoothing etch procedure appeared insufficient to remove all the surface contamination, wafer re-preparation is done by a chemo-mechanical polishing procedure.
TL;DR: In this article, the authors extended this previous work by putting measurements on a more rigorous basis and by improving the experimental efficiency of selected cells to beyond 43%, the highest reported to date for any combination of photovoltaic devices.
Abstract: One way of improving the efficiency of solar cells is to subdivide the broad solar spectrum into smaller energy ranges and to convert each range with a cell of appropriately matched bandgap. The most common approach to implementing this idea has been to use a monolithic or mechanical stack of cells arranged in order of increasing bandgap, with the highest bandgap cell uppermost. This provides automatic filtering of incident sunlight so that each cell absorbs and converts the optimal spectral range. The potential of an earlier experimental approach based on steering light in different wavelength bands to non-stacked cells recently has been re-explored with good results. The present work extends this previous work by putting measurements on a more rigorous basis and by improving the 'composite' experimental efficiency of selected cells to beyond 43%, the highest reported to date for any combination of photovoltaic devices.
TL;DR: In this paper, an elegant laser tailoring add-on process for silicon solar cells, leading to selectively doped emitters increases their efficiency h by Dh ¼ 0.5% absolute.
Abstract: An elegant laser tailoring add-on process for silicon solar cells, leading to selectively doped emitters increases their efficiency h by Dh ¼0.5% absolute. Our patented, scanned laser doping add-on process locally increases the doping under the front side metallization, thus allowing for shallow doping and less Auger recombination between the contacts. The selective laser add-on process modifies the emitter profile from a shallow error-function type to Gaussian type and enables excellent contact formation by screen printing, normally difficult to achieve for shallow diffused emitters. The significantly deeper doping profile of the laser irradiated samples widens the process window for the firing of screen printed contacts and avoids metal spiking through the pn-junction. Copyright # 2010 John Wiley & Sons, Ltd.
TL;DR: In this paper, a process monitoring and quality assessment for Cu(In,Ga)(Se,S)2 (CIGS) absorber layers is discussed, where laser light scattering (LLS) is used as a tool for process diagnostics.
Abstract: Process monitoring and quality assessment for Cu(In,Ga)(Se,S)2 (CIGS) absorber layers is discussed. One focus is on laser light scattering (LLS) as a tool for process diagnostics. This technique can give in situ and real-time information about CIGS film growth using sequential as well as evaporation processes. Raman spectroscopy is presented as a method to assess the fundamental structural properties of as-grown films. Experience shows that the specific structure of Raman lines can be interpreted in relation to device performance. Raman spectroscopy is particularly useful for material development and achieving at least average solar cell efficiencies. Time-resolved photoluminescence (TRPL) goes one step further and is generally related to the solar cell performance. It tracks carrier population decay after optical excitation and thus gives quantitative information about the most efficient recombination channels and material quality. It is apt to optimise the absorber of highly efficient devices. We will recommend how to use the three methods appropriately and will discuss requirements for industrial applications. Copyright © 2010 John Wiley & Sons, Ltd.
TL;DR: In this article, an approach to determine the operating voltage of individual solar cells in photovoltaic (PV) modules by electroluminescence (EL) imaging was introduced.
Abstract: We introduce an approach to determine the operating voltage of individual solar cells in photovoltaic (PV) modules by electroluminescence (EL) imaging. The highest EL signal of each solar cell is proportional to its operating voltage. Moreover the sum of all operating voltages equals the externally applied module voltage. Thus the operating voltage of individual solar cells is determined from the measured EL signal. The reliability of this relation is verified by measurements on specially prepared PV modules allowing us to measure the individual operating cell voltage. The experimentally measured cell voltages are deduced with an uncertainty of ±1% from an EL image.
Moreover, the operating cell voltages determined from the EL image are used to calculate the module series resistance. Comparing experimentally determined values from the operating cell voltage and the total current flowing supplied to the module with calculated module series resistances using tabulated material and typical solar cell parameters, a very good correspondence is found. Copyright © 2010 John Wiley & Sons, Ltd.
TL;DR: In this article, the influence of the composition of screen printing metal pastes on contacting boron emitters for crystalline silicon solar cells, optimized on the basis of commercial Ag-paste Ferro 3347 by adding silicon and aluminum.
Abstract: This paper analyzes the influence of the composition of screen printing metal pastes on contacting boron emitters for crystalline silicon solar cells, optimized on the basis of commercial Ag-paste Ferro 3347 by adding silicon and aluminum. Aluminum provides a lower contact resistance, while silicon prevents the spiking and alloying of aluminum with the silicon of the substrate. The best pastes have turned out to be high Si-concentrated, which have provided a final specific contact resistance of 3–4 mΩ cm2 on screen printed boron emitters diffused at 1000°C for 8 min, with shunt conductance lower than 0.6 mS/cm2. The final fill factors have been better than 77.5% and open circuit voltages have exceeded 605 mV on Czochralski (Cz) n type 0.7 Ω cm solar cells. These results have proven the feasibility of our screen printing process for p+nn+ structures. Copyright © 2009 John Wiley & Sons, Ltd.
TL;DR: In this article, the results of silicon wire-sawing experiments were discussed in relation to assumptions underlying the rolling-indenting model, which describes the process, and the measured parameters were found to vary along wire direction, between the entrance of the wire in the ingot and its exit.
Abstract: Silicon wafer wire-sawing experiments were realized with different sets of sawing parameters, and the thickness, roughness, and cracks depth of the wafers were measured. The results are discussed in relation to assumptions underlying the rolling-indenting model, which describes the process. It was also found that the silicon surface at the bottom of the sawing groove is different from the wafer surface, implying different sawing conditions in the two positions. Furthermore, the measured parameters were found to vary along the wire direction, between the entrance of the wire in the ingot and its exit. Based on these observations, some improvements for the wire-sawing model are discussed. Copyright (C) 2010 John Wiley & Sons, Ltd.
TL;DR: In this article, it is shown that fitting the two-diode model is inappropriate to quantify recombination in the space charge region and ohmic losses due to series resistance, and an advanced current-voltage curve analysis including fill factors and fit is presented.
Abstract: After completion of the solar cell manufacturing process the current–density versus voltage curves (J(U) curves) are measured to determine the solar cell's efficiency and the mechanisms limiting the efficiency. An accurate and robust analysis of the measured curves is essential. In this work it is shown that fitting the two-diode model is inappropriate to quantify recombination in the space charge region and ohmic losses due to series resistance. Three fill factors, namely the fill factor of the illuminated J(U) curve, the pseudo fill factor of the sunsVoc curve and the ideal fill factor of the single diode model, are the base of a quick loss analysis that is evaluated in the present paper. It is shown that for an accurate analysis the distributed character of the series resistance and the network character of the solar cell cannot be neglected. An advanced current–voltage curve analysis including fill factors and fit is presented. Copyright © 2010 John Wiley & Sons, Ltd.
TL;DR: In this paper, a ZnO nanorod antireflective coating has been prepared on Cu(In,Ga)Se 2 thin film solar cells, which leads to a decrease of the weighted global reflectance of the solar cells from 8.6 to 3.5%.
Abstract: A ZnO nanorod antireflective coating has been prepared on Cu(In,Ga)Se 2 thin film solar cells. This coating leads to a decrease of the weighted global reflectance of the solar cells from 8.6 to 3.5%. It boosts the solar cells short-circuit current up to 5.7% without significant effect on their open-circuit voltage and fill factor (FF), which is comparable to a conventional optimized single layer MgF 2 antireflective coating. The ZnO nanorod antireflective coating was electrochemically prepared from an aqueous solution at 80°C. The antireflective capability of ZnO nanorod arrays (ZNAs) may be further improved by optimization of growth conditions and their geometry. Copyright © 2010 John Wiley & Sons, Ltd.
TL;DR: In this paper, a lumped diode model for concentrator multijunction solar cells, in which the temperature, irradiance and spectrum dependences are explicitly included, is presented.
Abstract: We describe here a lumped diode model for concentrator multijunction solar cells, in which the temperature, irradiance and spectrum dependences are explicitly included. Moreover an experimental method based on it for the prediction of the I-V curve under any irradiance-spectrum-temperature conditions from a single input measurement is proposed and applied to a set of commercial triple-junction solar cells in order to demonstrate its validity. Component ‘isotype’ cells are used as reference cells for intensity and spectrum, sparing the measurement of light spectrum and cell spectral response. Finally, a mean RMS prediction error of 0.85% over a range of 100X-25°C to 700X-75°C is reported for the whole set when the model parameters inherent in the cell are assumed to be the same for every sample. If optimum parameters are extracted for every cell, the RMS error is reduced to 0.53%. Copyright © 2010 John Wiley & Sons, Ltd.
TL;DR: In this article, the authors present a method for estimating the energy output from one-axis tracking non-concentrating PV systems and compare the yields from different configurations, based on the use of solar radiation and temperature databases.
Abstract: We present a method for estimating the energy output from one-axis tracking non-concentrating PV systems and compare the yields from different configurations. The method is based on the use of solar radiation and temperature databases and models for the performance of PV modules under given geographic conditions. In the resulting maps of energy yield for Europe it is found that there are two different one-axis configurations that perform almost as well as a full two-axis sun-tracking system: one with a vertical axis and inclined modules, and the other with an inclined axis directed north–south and modules in the plane of the axis. When the inclination angles of the modules are optimized, these two configurations have an energy yield compared to an optimal fixed mounting that is approximately 30% higher in southern Europe, about 20–25% higher in central Europe, and up to 50% higher in northern Scandinavia. Compared to the two-axis tracking, the yields are only 1–4% lower, making such one-axis tracking systems very attractive in terms of performance relative to technical complexity and price. Copyright © 2010 John Wiley & Sons, Ltd.
TL;DR: In this paper, a fast method to count cracks with good statistics over approximately 4000 mm of sample cross-section was introduced, which was proven to be useful to quickly visualize the impact of substrate morphology on the density of cracks in microcrystalline and in micromorph devices, which is an important issue in the manufacturing process of modules.
Abstract: Microcrystalline silicon (mc-Si:H) cells can reach efficiencies up to typically 10% and are usually incorporated in tandem micromorph devices. When cells are grown on rough substrates, ‘‘cracks’’ can appear in the mc-Si:H layers. Previous works have demonstrated that these cracks have mainly detrimental effects on the fill factor and open-circuit voltage, and act as bad diodes with a high reverse saturation current. In this paper, we clarify the nature of the cracks, their role in postoxidation processes, and indicate how their density can be reduced. Regular secondary ion mass spectrometry (SIMS) and local nano-SIMS measurements show that these cracks are prone to local post-oxidation and lead to apparent high oxygen content in the layer. Usually the number of cracks can be decreased with an appropriate modification of the substrate surface morphology, but then, the required light scattering effect is reduced due to a lower roughness. This study presents an alternative/complementary way to decrease the crack density by increasing the substrate temperature during deposition. These results, also obtained when performing numerical simulation of the growth process, are attributed to the enhanced surface diffusion of the adatoms at higher deposition temperature. We evaluate the cracks density by introducing a fast method to count cracks with good statistics over approximately 4000 mm of sample cross-section. This method is proven to be useful to quickly visualize the impact of substrate morphology on the density of cracks in microcrystalline and in micromorph devices, which is an important issue in the manufacturing process of modules. Copyright#2010 John Wiley & Sons, Ltd.
TL;DR: In this paper, the thermal cycling durability of large-area Pb-free (Sn3.5Ag) solder between silicon semiconductor and copper interconnects in photovoltaic (PV) cells is assessed and compared to benchmark results from Pbbased (Sn36Pb2Ag) PV cells.
Abstract: The thermal cycling durability of large-area Pb-free (Sn3.5Ag) solder between silicon semiconductor and copper interconnects in photovoltaic (PV) cells is assessed and compared to benchmark results from Pb-based (Sn36Pb2Ag) PV cells. Accelerated thermal cycling tests have been conducted on PV cells of both solder compositions, and the increase in series resistance due to interconnect damage has been characterized using in situ dark I-V measurements. Both the Pb-free and Pb-based cells show a steep initial rise followed by a steady rate of increase in degradation histories, with the Pb- free cells showing a more pronounced 'knee' in the degradation curves. Extrapolation of the degradation data for both solders suggests that Pb-free cells are four times more durable than the Pb-based cells at the test condition. This superior thermal cycling fatigue durability of Pb-free cells was also confirmed with physics of failure (PoF) analysis, consisting of nonlinear finite element (FE) stress analysis and an energy-partitioning (E-P) solder fatigue model. FE models error-seeded with manufacturing voids in the solder interconnect predicted a significant reduction in the thermal cycling durability with increasing solder void density. However, even the most voided Pb-free cells modeled are predicted to be twice as durable as void-free Pb-based cells, under the accelerated temperature cycle used in the test. The acceleration factor (AF) predicted by the PoF analysis for a typical service environment is three times higher for Pb-free cells than that for Pb-based cells.
TL;DR: In this article, a-Si:H solar cell with the optimal periodic texture parameters (period of 300nm, height of 300 nm, and duty cycle of 50%) and the absorber layer thickness of 300 µm was shown to generate up to 35% more photocurrent in comparison to the cell with flat interfaces.
Abstract: Optical analysis of hydrogenated amorphous silicon (a-Si:H) solar cells with a periodic texture applied to the interfaces was carried out by two-dimensional optical simulator. The optical simulator solves the electromagnetic wave equations by means of finite element method using triangular elements for the discretization of space. The periodic texture with rectangular-like shape acts as a diffraction grating which scatters light into selective angles and thus gives a potential for significant prolongation of optical paths in thin absorber layers of the cells. Optimization of the geometrical parameters (period, height and duty-cycle) of the periodic texture was carried out in order to obtain the highest photocurrent from a-Si:H solar cells. The a-Si:H solar cell with the optimal periodic texture parameters (period of 300 nm, height of 300 nm and duty cycle of 50%) and the absorber layer thickness of 300 nm generates up to 35% more photocurrent in comparison to the cell with flat interfaces. The optical analysis demonstrates that the optimal periodic texture in the a-Si:H solar cell results in the best trade-off between the antireflection effect at front interfaces, light scattering efficiency and the absorption losses at realistic metal back contact. Copyright © 2010 John Wiley & Sons, Ltd.
TL;DR: In this paper, two novel organic dyes were synthesized using electron rich phenothiazine as electron donors and oligothiophene vinylene as conjugation spacers.
Abstract: Two novel organic dyes have been synthesized using electron rich phenothiazine as electron donors and oligothiophene vinylene as conjugation spacers. The two dyes (2E)-2-cyano-3-(5-(5-((E)-2-(10-(2 ...
TL;DR: In this article, the authors present a study of long-term outdoor performance of a-Si and hybrid modules mounted in the same location over several years and demonstrate that the performance improves due to annealing when the module temperature is higher.
Abstract: This paper presents a study of long-term outdoor performance of a-Si and hybrid modules mounted in the same location over several years. The modules were also characterized indoors using standard measurement methods employing pulsed solar simulators at the European Solar Test Installation (ESTI). The present study is intended to contribute to future standards on energy rating by presenting a common procedure for correcting the outdoor performance measurements to standard test conditions and comparing the resulting module performance at real and laboratory conditions. A seasonal variation in output, higher in the summer and lower in the winter, suggests that the module performance improves due to annealing when the module temperature is higher. The total output energy per month for these two technologies and a reference c-Si technology is also presented. Copyright # 2010 John Wiley & Sons, Ltd.
TL;DR: In this article, an algorithm to separate both front and back surface recombination velocities and minority carrier diffusion length from photoluminescence (PL) images on silicon wafers is introduced.
Abstract: Spontaneous photoemission of crystalline silicon provides information on excess charge carrier density and thereby on electronic properties such as charge carrier recombination lifetime and series resistance. This paper is dedicated to separating bulk recombination from surface recombination in silicon solar cells and wafers by exploiting reabsorption of spontaneously emitted photons. The approach is based on a comparison between luminescence images acquired with different optical short pass filters and a comprehensive mathematical model. An algorithm to separate both front and back surface recombination velocities and minority carrier diffusion length from photoluminescence (PL) images on silicon wafers is introduced. This algorithm can likewise be used to simultaneously determine back surface recombination velocity and minority carrier diffusion length in the base of a standard crystalline silicon solar cell from electroluminescence (EL) images. The proposed method is successfully tested experimentally. Copyright © 2009 John Wiley & Sons, Ltd.
TL;DR: In this article, a-Si:H/µc-Si0.9Ge0.1:H solar cell with bottom cell thickness less than 1'µm was proposed to reduce the thickness of the bottom cell while preserving the current matching with hydrogenated amorphous silicon top cell.
Abstract: We have fabricated efficient (∼7–8%) hydrogenated microcrystalline Si1–xGex (µc-Si1–xGex:H, x ∼ 0.1–0.17) single junction p-i-n solar cells with markedly higher short-circuit current densities than for µc-Si:H (x = 0) solar cells due to enhanced infrared absorption. By replacing the conventional µc-Si:H with the µc-Si1–xGex:H as infrared absorber in double junction tandem solar cells, the bottom cell thickness can be reduced by more than half while preserving the current matching with hydrogenated amorphous silicon (a-Si:H) top cell. An initial efficiency of 11.2% is obtained for a-Si:H/µc-Si0.9Ge0.1:H solar cell with bottom cell thickness less than 1 µm. Copyright © 2009 John Wiley & Sons, Ltd.
TL;DR: In this paper, a simple and facile method for directly growing self-organized TiO 2 nanotubular arrays around the whole Ti mesh by electrochemical anodization in organic electrolytes and their application in all-Ti dye-sensitized solar cells (DSSCs) was reported.
Abstract: This paper reports a simple and facile method for directly growing self-organized TiO 2 nanotubular arrays around the whole Ti mesh by electrochemical anodization in organic electrolytes and their application in all-Ti dye-sensitized solar cells (DSSCs). Compared with the traditional fluorine-doped tin oxide (FTO)-based DSSC and the backside illuminated DSSC, this type of DSSC showed advantages such as low resistance, cheap fabrication cost and enhanced sunlight utilization. Different thicknesses of nanotubular array layers were investigated to find their influence on the photovoltaic parameters of the cell. We also considered three types of meshes as the substrates of anodes and found that the cell with 6 openings/mm 2 exhibited the highest conversion efficiency of 5.3%. The area of the cell had only a little impact on the photovoltaic performances.