Vertical Multijunction Solar Cell Research Articles

Analysis of vertical multijunction solar cells

ABSTRACTThe electrical parameters saturation current density; series resistance; shunt resistance; ideality factor and photocurrent density of multi-junction solar cells have been extracted from characteristics data J-V. We found that experimental results on photo-current voltage characteristics can be reliably reproduced using electrical extraction parameters using the non-linear least-squares method. We realized high voltage silicon solar modules with a voltage of up to Voc =25.491 V at 500 suns.

Effects of Solar Concentration on Efficiency for Vertical Multijunction Silicon Solar Cells

In this work, we have analyzed the characteristic J-V of vertical multijunction solar cells. We have also offered a design of a monolithic compact solar module with cells electrically connected in series. The extracting of the electrical parameters of multi-junction solar cells from characteristics data J-V such as: J0, saturation current density; Rs, series resistance; Rsh, shunt resistance; n, ideality factor and Jph, photo current density which are obtained with light concentration have been studied. The short circuit current increases with increasing the concentration in a linear manner and the saturation current is not constant and increases with increasing the concentration. We have studied the effect of sun concentration on the open circuit voltage of vertical multijunction. The shunt resistance, Rsh plays a vital role in health monitoring of solar cells in the spacecraft power system. The value of Rsh has been obtained in range 1–500 suns.

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

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

Ultrasound assisted nickel plating and silicide contact formation for vertical multi-junction solar cells

Vertical multijunction (VMJ) silicon solar cells (SC) are considered the most preferred among all known single-crystal ones for using in various photovoltaic systems under conditions of highly concentrated sunlight. The techniques of ultrasound assisted nickel plating (USNiP) of mirror polished silicon wafers and their subsequent vacuum annealing for VMJ SC ohmic contacts creating were tested by X-ray diffractometry, scanning electron microscopy and dark current–voltage characteristics. The feasibility of utilizing nickel electroplating in the sulfamate electrolyte for the NiSi ohmic contact made on the mirror polished silicon wafers with n+–p junctions on both sides have been experimentally confirmed. Ultrasound assistance of the nickel plating insured the enhancement of NiSi adhesion and improving the quality of the ohmic contacts.

Analysis of effects of front and back surface dopants on silicon vertical multi-junction solar cell by 2D numerical simulation

The silicon vertical multi-junction (VMJ) solar cell has a good potential in high concentration, but it requires high quality front and back surface passivation layers to keep its high efficiency. We try to add dopants into the front and back surfaces of the VMJ cell to release this strict requirement in this work. The effects of recombination velocities, doping types and doping profiles of front and back surfaces on the performance of the P-type VMJ cell were calculated under 1 sun and 1000 suns. The 2D numerical simulation tool TCAD software was used. The performance of the VMJ cell without front and back surface dopants was also calculated for comparison. It was found that the requirement of high quality front and back surface passivation layers could be released remarkably by adding either N-type or P+-type front and back surface dopants. For the two types of front surface dopants, the highest efficiencies of the cells were got by light dopant; for the two types of back surface dopants, the doping type and profile affected little on the performance of the cell in our calculation range. It was also found that the series resistance of the VMJ cell with N-type front surface dopant was decreased by the 2D effect of front surface emitter. The VMJ cell with P+-type front surface dopant had the highest efficiency under 1000 suns and the VMJ cell with N-type front surface dopant had the highest efficiency under 1 sun in our calculation range.

Performance analysis of vertical multi-junction solar cell with front surface diffusion for high concentration

The vertical multi-junction (VMJ) solar cell has good potential applications in high concentration photovoltaic. The efficiency of VMJ cell reached to 19.19% under 2480 suns has been reported. Numerical calculations show that the efficiency can reach close to 30% after optimization. In this work, the performance of the silicon VMJ cell with front surface diffusion working under 1 sun and 1000 suns was calculated numerically using a TCAD software. The front surface diffusion can reduce the requirement of high quality front surface passivation, but increases the series resistance. The effect of the N-type emitter dopant profile, P+-type back surface field dopant profile, width, thickness, bulk doping concentration and lifetime of the sub-cell on the performance of the VMJ cell with front surface diffusion was calculated and analyzed. The efficiency reached to 30.56% under 1000 suns after optimization.

Optimization of Subcell Interconnection for Multijunction Solar Cells Using Switching Power Converters

A multijunction solar cell can extract higher solar energy compared to a single junction cell by splitting the solar spectrum. Although extensive research on solar cell efficiency enhancement is in place, limited research materials are available to identify the optimum interconnection of multijunction solar subcells using power electronic circuits. Multijunction solar cells could be grouped into two main categories: vertical multijunction (VMJ) solar cells and lateral multijunction (LMJ) solar cells. In this paper, a detailed study to identify the optimum interconnection method for various multijunction solar cells has been conducted. The authors believe that the conducted research in this area is very limited, and an effective power electronic circuit could substantially improve the efficiency and utilization of a photovoltaic (PV) power system constructed from multijunction solar cells. A multiple input dc-to-dc boost converter has been used to demonstrate the advantage of the proposed interconnection technique. In order to ensure maximum power point (MPP) operation, a particle swarm optimization (PSO) algorithm has been applied needing only one MPP control for multiple solar modules resulting in cost and complexity reduction. The PSO algorithm has the potential to track the global maxima of the system even under complex illumination situations. A complete functional system with the implementation of the proposed algorithm has been presented in this paper with relevant experimental results.

Refilling Silicon Grooves by Liquid Phase Epitaxy

Planar epitaxial refilling of grooves etched in (110) oriented silicon wafers has been achieved by using a liquid phase epitaxial growth process. This process has the advantages of requiring lower processing temperatures, maintaining high minority carrier lifetime, and of not producing the undesirable polycrystalline deposits invariably observed on the oxide‐coated surfaces between the grooves during conventional vapor phase epitaxial growth. The effect of epitaxial growth conditions on the planar refill has been examined. It has been found that planar refill can be achieved at slow cooling rates on the order of 0.1–0.2°C/min in the presence of an oxide layer between the grooves to be refilled. At high cooling rates and in the absence of the oxide layer between the grooves, nonplanar surfaces are observed. Typical applications for this planar epitaxial refill process would be in the fabrication of vertical multijunction solar cell structures and in the fabrication of vertically walled gate regions for power junction field effect transistors and field controlled thyristors.

Lamellar devices processed by thermomigration

Lamellar structures consisting of alternate p- and n-type silicon layers were fabricated by migrating molten aluminum-rich wires through n-type silicon wafers in a thermal gradient. The recrystallized material deposited behind the molten wires was p type. An aluminum-dopant concentration profile was calculated which was consistent with the measured electrical characteristics of the lamellar structures. Lamellar devices made from these structures can be used as vertical multijunction solar cells, high-voltage diodes, surge protectors, and negative-incremental resistors.

Reply to ’’New analysis of a high-voltage vertical multijunction solar cell’’

An analysis is presented which demonstrates that a vertical multijunction solar cell with covering lens does have optimum dimensions. The analysis does point out that the optimum dimensions would indeed eliminate any dark junctions in series with illuminated junctions for maximum efficiency. Thus, back-to-back p-n junctions should not be designed into a solar cell.

New analysis of a high-voltage vertical multijunction solar cell

We present an analysis and a model for a vertical multijunction solar cell with covering lens, for which a 21% efficiency has been predicted previously. It is shown that the maximum conversion efficiency is in fact about 0.3%. The present analysis confirms our belief that back-to-back diodes should be designed into a solar cell only with great caution.

The lensed high-voltage vertical multijunction solar cell

The vertical multijunction solar cell with covering lens is a photovoltaic device which promises high-voltage, high-efficiency outputs. The structure described here is a modification of a structure previously reported. It is shown that the original high-voltage vertical multijunction solar cell is capable of high voltages but not high efficiencies. The solar cell described here is capable of higher efficiencies, but a more detailed analysis than presented here is necessary before a comparison between this cell and a conventional solar cell can be made.

High-voltage vertical multijunction solar cell

The vertical multijunction solar cell with covering lens is a photovoltaic device which promises efficiencies greater than that predicted under ideal conditions for any other structure. The mathematical analysis presented here illustrates this statement. In addition the structure described here is capable of a high-voltage output for small solar cell dimensions, a feature which makes this device attractive for many applications where other designs are impractical. The analysis predicts the output short-circuit current, open-circuit voltage, maximum power, and an efficiency of 21% for a silicon homojunction solar cell.

Performance of diffused vertical multijunction solar cell

Performance of diffused vertical multijunction solar cell

Analysis of vertical multijunction solar cells using a distributed circuit model

Vertical multijunction (VMJ) solar cells have generated considerable interest due to their improved performance in terms of conversion efficiency and radiation tolerance compared to the conventional planar solar cells. Fabrication of VMJ cells with junction density of 2000 junctions/cm is now possible using advanced fabrication technologies. This work describes an analysis of some of the VMJ cell structures now being fabricated—especially the ones that combine the enhanced red response and radiation tolerance of the VMJ concept and blue response of conventional planar cells. A distributed equivalent circuit model is used for analysis of complicated junction configurations—which otherwise would be very cumbersome using conventional carrier transport equations. The VMJ cell structures were analyzed to study their device characteristics and their sensitivity to various material and fabrication parameters such as epitaxial layer resistivity and carrier lifetimes. The results show that the conversion efficiency is higher than conventional devices due to efficient carrier collection with a superior radiation tolerance. The cells, however, degrade more rapidly compared to planar cells at higher radiation levels determined by the structural parameters.

On etching very narrow grooves in silicon

The etch rate on the {110} is shown to be at least 400 times faster than that on the {111} using 44% KOH : H2O at a temperature of 85 °C and below. A model is presented which attributes essentially all the etching on the near {111} planes to the misorientation ledges. Grooves of 0.6−μm width and 44−μm depth have been produced. Such grooves have been used to make high−value SiO2 capacitors and vertical multijunction solar cells.

Vertical multijunction solar-cell one-dimensional analysis

The vertical multijunction solar cell is a photovoltaic device which may allow conversion efficiencies higher than conventional planar devices. A one-dimensional model of the device is presented here which allows a simple and straightforward analysis of device performance to be conducted. The analysis covers the derivation of device short-circuit current, saturation current, open-circuit voltage, and maximum power as a function of illumination spectra, device geometry, and device material properties.