Solar Junction’s World Record of 43.5 % efficiency for concentrated photovoltaic Cell

Recently, Solar Junction, A developer of high efficiency multi-junction cells for the concentrated photovoltaic (CPV) market, has achieved world-record for 43.5 percent efficiency on a commercial-ready 5.5 mm x 5.5 mm production cell.

                   

This record is just a step in direction of improvement with hope of much better achievement in concentrated photovoltaic cell. Efficiency is always important in photovoltaic, but it's probably even more important in CPV.The accomplishment of high efficiencies for devices based on Moderated Photovoltaic i.e concentrated photovoltaic technology has made a hope that concentrated photovoltaic will provide viable solution for solar energy to be treated as real alternate energy resource in near future.
The Solar Energy, being abundantly available on the earth, is counted as most applicable alternate source of energy. Sunlight is composed of photons or particles of solar energy; where these photons contain various amounts of energy corresponding to the different wavelengths of the solar spectrum. The "photovoltaic effect" is the basic physical process through which a PV cell converts sunlight into electricity. When photons strike a PV cell, they may be reflected or absorbed, or they may pass right through, and only the absorbed photons generate electricity. The energy of the photon gets transferred to an electron in an atom of the cell which is actually a semiconductor. The conversion efficiency of a PV cell is the proportion of sunlight energy that the cell converts to electrical energy. But today's PV devices convert just 7%-17% of light energy into electric energy. The efficiency is strongly temperature dependent. As the temperature is raised, the internal resistance of the material increases and the electrical conductivity decreases. The fundamental physical limitation in production photovoltaic cells is this decrease in efficiency as the temperature of the cell increases. Because of this, for a material like silicon, the operating efficiency of a photovoltaic array will probably never be higher than 20% and will most likely be between 5 and 15%. Although research and development for conventional silicon and thin film technologies are still under way, there’s plenty of other innovation going on in other PV areas as well that could help bring down the cost of solar energy.CPV is one of several solar technologies providing value in utilizing the sun as a clean, renewable source of power. Each of these solar technologies suits to relevant applications and operating environments. The key is in selecting the right solar technology for the right applications. In areas where the solar resource is high, CPV is usually the best solution to deliver low-cost solar energy; but clouds and overcast conditions create diffused light that essentially cannot be concentrated. A concentrating photovoltaic (CPV) system converts light energy into electrical energy in the same way that conventional photovoltaic technology does, but the difference in the technologies is addition of an optical system in the concentrating photovoltaic (CPV) system that focuses a large area of sunlight onto small, highly efficient solar cell. At the heart of a CPV system is a high-efficiency, multi-junction solar cell. So, the Concentrating Photovoltaics (CPV) delivers industry-best efficiency by utilizing low-cost optics and precise 2-axis tracking to concentrate light onto the highest-efficiency solar cells. Solar concentrators of all varieties may be used with the base technology either being refractive or reflective. The other primary difference is in the cells and the traditional PV systems utilize large amounts of silicon solar cells, whereas the CPV systems utilize a small amount of high-efficiency solar cell material. These cells used in high concentration CPV systems are referred to as multijunction or III-V cells which were originally created for space applications. These cells provide energy conversion efficiencies much higher than traditional silicon cells. The fact that the CPV cells do not degrade in performance when temperatures are high provides another advantage to CPV in the high solar resource areas where high temperatures are common. CPV systems also track the sun throughout the day which correlates to more energy production that is an excellent match to peak demand load. CPV systems will produce electricity at a steady rate late into the day, a capability not available to fixed tilt PV systems. CPV, with its higher efficiency delivers higher energy production per megawatt installed, provides the lowest cost of solar energy in high solar regions of the world. The CPV can harvest more energy and become a leading power-generating technology in regions of high solar resource.

Solar Junction’s cells achieving 43.5 percent efficiency incorporate the company’s proprietary adjustable spectrum lattice-matched, A-SLAM, technology, which enables to optimally partition the solar spectrum for maximum efficiency and greater reliability. Lattice-matched means that the boundaries of different semiconductor materials, i.e., their junctions, don't strain or shift during operation. It's an indication of the structural compatibility of two materials. Strain at the boundary of the materials can cause dark-line defects and other faults that negatively influence the performance and lifetime of these sophisticated solar cells. The Adjustable Spectrum Lattice Matched (A-SLAM™) multi-junction solar cell architecture provides material bandgap tunability – particularly from 0.8 to 1.42 eV - to maximize the absorbed sunlight within CPV modules, thereby increasing the efficiency and energy harvested. The ultra-concentration tunnel junctions of Solar Junction also contributed a lot to attain this achievement as they allow cells to perform optimally at 1000-1300 or more sun concentrations. A peak efficiency of 43.5 percent was measured at greater than 400 suns and still maintained efficiency as high as 43 percent out to 1,000 suns. The cell’s efficiency was confirmed by NREL’s Measurement and Characterization Laboratory. Increases in CPV cell efficiencies are a key driver for improving CPV economics, with each cell efficiency gain leveraged and multiplied in value by the components that account for the remaining 80 percent of total system costs. Modest gains in CPV cell efficiency can translate to significant reduction in levelized cost of energy (LCOE), so the increase is not trivial and bodes well for continued progress for the startup and the CPV industry as a whole. Levelized Cost of Energy ‘LCOE’, basically is the net present value of the total cost of generating energy, divided by the amount of energy produced. It is used as a metric for evaluating energy options, because it encompasses all of the costs and measures that against the amount of energy generated, providing a much more appropriate measure than such metrics as $/watt which fail to take into account actual energy production. Levelized cost of energy also allows solar energy to be compared with other forms of renewable and conventional energy. According to the firm, a one percent improvement in efficiency at the cell level can result in a three percent to four percent reduction in the cost of the. The achievement for 43.5 percent efficiency on a commercial-ready production cell was, in part, supported under the U.S. Department of Energy (DOE) PV Incubator Program, managed through DOE’s National Renewable Energy Laboratory (NREL).