HZB with the new cell exceeds its previous record of a 29.8% efficiency with a tandem cell from last year, and that of a Switzerland’s Ecole Polytechnique Fédérale de Lausanne (EPFL), which had reached an efficiency of 31.3% earlier this year with a similar technology. Tandem devices outstrip other technologies in efficiency by stacking cell layers with different materials on top of each other to harvest a larger part of the light spectrum. The system consists of a silicon bottom cell and a perovskite top cell. Glenn welcomes co-development opportunities.Researchers at the Heimholtz Zentrum Berlin (HZB) have developed a tandem solar cell that converts 32.5% of the sun’s radiation into electricity, a new world record for this type of technology, according to certifying institute European Solar Test Installation (ESTI) in Italy. This is an early-stage technology requiring additional development. This unprecedented combination of increased efficiency and cost savings has considerable commercial potential. The resultant high performance multi-junction photovoltaic cell with the selenium interlayer provides more power per unit area while utilizing a low-cost silicon-based substrate. To obtain even higher efficiencies of over 40%, both the top and bottom layers can be multi-junction solar cells with the selenium layer sandwiched in between. The three-junction solar cell manufactured using selenium as the transparent interlayer has a higher efficiency, converting more than twice the energy into electricity than traditional cells. The selenium interlayer acts as a connective layer between the top cell that absorbs the short-wavelength light and the bottom silicon-based cell that absorbs the longer wavelengths. The selenium interlayer is applied between the top and bottom wafers, then pressure annealed at 221☌ (the melting temperature of selenium), then cooled. To further improve the efficiencies, this cell has three junctions, where the top wafer is made from high solar energy absorbing materials that form a two-junction cell made from the III-V semiconductor family, and the bottom substrate remains as a simple silicon wafer. A multi-junction photovoltaic cell differs from a single junction cell in that it has multiple sub-cells (p-n junctions) and can convert more of the sun's energy into electricity as the light passes through each layer. This NASA Glenn innovation is a novel multi-junction photovoltaic cell constructed using selenium as a bonding material sandwiched between a thin film multi-junction wafer and a silicon substrate wafer, enabling higher efficiencies. For terrestrial applications, it can provide unprecedented efficiencies for auxiliary power units in vehicles, solar roof tiles, power plants, and smart grid systems. This high-efficiency solar technology takes advantage of inexpensive silicon wafers and provides a more robust design for next-generation solar cells in space. This approach enables a cell that is simultaneously lower in cost, more rugged, and more efficient than existing space-based photovoltaic cells. The innovation allows a multi-junction solar cell to be developed without the constraint of lattice matching, and with a low-cost, robust silicon wafer as the supporting bottom substrate and bottom cell. Selenium is a unique semiconductor in that its transparent to light at photon energies below the band gap (infrared), enabling light to pass from the multi-junction top cell to the silicon-based bottom cell. Innovators at NASA's Glenn Research Center have developed a high-efficiency multi-junction solar cell that uses a thin interlayer of selenium as the bonding material between wafers.
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