AMP_06_September_2021

A D V A N C E D M A T E R I A L S & P R O C E S S E S | S E P T E M B E R 2 0 2 1 1 2 WORLD-RECORD SOLAR CELL EFFICIENCY A solar cell developed by research- ers at Germany’s Fraunhofer Institute for Solar Energy Systems ISE achieved a new world record for conversion efficiency of 26% for both-sides con- tacted silicon solar cells. The structure of the record-breaking cell presents fundamental design-related charac- teristics that could lead to even higher efficiencies—specifically, the design of the back-side cell surface as a full area charge carrier that collects passivating contact. Tunnel oxide passivating contact (TOPCon) technology, developed at Fraunhofer, forms the basis for the re- cord cell. This technology combines the advantages of very low surface recom- bination losses with efficient charge carrier transport. Their TOPCon rear emitter solar cell allows higher voltag- es and higher fill factors than cells with a collecting emitter on the front side. With this cell design, the wafer can be better utilized for charge carrier trans- port and the front side, using aluminum oxide, is more effectively passivated. Power loss analysis shows that this cell generally compensates for and mini- mizes both electron and hole transport losses. The cell structure has a major advantage in that the subsequent pro- duction step—connecting the solar cells to form a module—can be based on ex- isting technologies, thus allowing the use of many standard techniques. www. ise.fraunhofer.de/en.html. SUSTAINABLE BATTERY ALTERNATIVE With the goal of making energy storage more economical, researchers at Cornell University, Ithaca, N.Y., are developing rechargeable batteries us- ing low-cost materials. Utilizing alumi- num, they demonstrated a new tech- nique resulting in reusable batteries that offer up to 10,000 error-free cycles. This new kind of battery could provide a safer and more environmentally friend- ly alternative to lithium-ion batteries, which currently dominate the market but are slow to charge and prone to combustion. Among the advantages of alumi- num is that it is abundant in the earth’s crust, it is trivalent and light, and it therefore has a high capacity to store more energy than many other metals. However, aluminum can be tricky to integrate into a battery’s electrodes. It ENERGY TRENDS reacts chemically with the glass fiber separator, which physically divides the anode and the cathode, causing the battery to short circuit and fail. The researchers’ solution was to design a substrate of interwoven carbon fibers that forms an even stronger chemical bond with aluminum. When the battery is charged, the aluminum is deposited into the carbon structure via covalent bonding. While electrodes in conventional rechargeable batteries are only 2D, this technique uses a 3D—or nonplanar—ar- chitecture and creates a deeper, more consistent layering of aluminum that can be finely controlled. The alumi- num-anode batteries can be reversibly charged and discharged one or more orders of magnitude more times than other aluminum rechargeable batteries under practical conditions. cornell.edu . Vianode, a division of Elkem, and Morrow Batteries, all based in Norway, have signed a memorandum of under- standing to develop a large-scale supply of anode materials for Morrow’s planned lithium-ion battery cell facility in Arendal, Norway. Vianode and Morrow will jointly develop both synthetic graphite and silicon-containing anode materials. elkem.com . BRIEF The TOPCoRE solar cell set a newworld record in e iciency. Courtesy of Fraunhofer-Gesellscha . This magnified image shows aluminum deposited on carbon fibers in a battery electrode. The chemical bond results in a rechargeable battery that is safer, less expensive, and more sustainable than the lithium-ion alternative. Courtesy of Cornell University.