Invention Platgorm

Solar energy is a clean and renewable source of energy. Solar cells usually consist of a semiconductor material that absorbs sunlight and generates electricity. However, the amount of sunlight that can be converted into electricity is limited. Standard single-junction solar cells are theoretically limited to a maximum power conversion efficiency (PCE) of 30 percent. This is the famous "Shockley–Queisser limit," which comes about from a trade-off between light absorption and charge carrier thermalization.

To overcome this limit and reach higher efficiencies, different designs for solar cells have been considered. For instance, hot-carrier solar cells (HCSCs) make use of the excess kinetic energy of photoexcited electrons (before they are lost as heat) to improve PCE. However, such designs have not managed to exceed the Shockley–Queisser limit in practice. This could be due to their sensitivity to "nonidealities." Put simply, deviations from ideal scenarios, such as due to imperfect design, nonoptimal materials, or operating conditions, reduces their PCE down to or below the Shockley–Queisser limit. Conversion strategies, therefore, need to consider the resiliency of solar cell designs against such nonidealities.

Against this backdrop, an international team of researchers tested the resilience of a novel solar cell architecture, a hot carrier multijunction solar cell (HCMJSC), to nonideal design with nonoptimal materials. The HCMJSC consisted of a panel with a thin hot carrier top junction series connected to a thick cold bottom junction. They compared its performance with those of the reference standards set by multijunction solar cells (MJSCs) and HCSC. Their results are published in the SPIE Journal of Photonics for Energy (JPE).

A team of researchers led by chemists at the U.S. Department of Energy's (DOE) Brookhaven National Laboratory has learned that an electrolyte additive allows stable high-voltage cycling of nickel-rich layered cathodes. Their work could lead to improvements in the energy density of lithium batteries that power electric vehicles.

The findings, published in Nature Energy, offer a remedy to notorious degradation problems that crop up for nickel-rich cathode materials, especially at high voltages. This research was conducted as part of the DOE-sponsored Battery500 Consortium, which is led by DOE's Pacific Northwest National Laboratory (PNNL) and is working to significantly increase the energy density of lithium batteries for electric vehicles.

Sha Tan, a co-first author and Ph.D. candidate at Stony Brook University conducting research with the Electrochemical Energy Storage group at Brookhaven Lab, was originally studying how an additive, lithium difluorophosphate (LiPO2F2), could be used to improve low-temperature performance of batteries. Out of curiosity, she tried using the additive for high voltage cycling at room temperature.

"I found if I pushed the voltage up to 4.8 volts (V), this additive really gives great protection over the cathode and the battery achieved excellent cycling performance," Tan said.

Protecting battery electrodes

Batteries consist of two electrical terminals—electrodes called the cathode and the anode—that are separated by another battery component, the electrolyte. Electrons go through an external circuit connecting the two electrodes and ions go through the electrolyte. Both shuttle back and forth between the electrodes during charge-discharge cycles.

Nickel-rich layered cathode materials promise high energy density for next-generation batteries when paired with lithium metal anodes. But those materials are prone to capacity loss. One of the main issues is particle cracking during high-voltage charge-discharge cycles. High voltage operation is important because the total energy stored in a battery, important for vehicle range, goes up as the useful operating voltage increases.

Researchers from the Network Research Institute at the National Institute of Information and Communications Technology (NICT) report the world's first demonstration of more than 1 petabit per second in a multi-core fiber (MCF) with a standard diameter of 0.125 mm.

The researchers, led by Benjamin J. Puttnam, constructed a transmission system that supports a record optical bandwidth exceeding 20 THz by exploiting wavelength division multiplexing (WDM) technology. It incorporates the commercially adopted optical fiber transmission windows known as C and L-bands and extends the transmission bandwidth to include also the recently explored S-band. Two kinds of doped fiber amplifiers, along with Raman amplification with pumps added in a novel multi-core pump combiner, enabled transmission of 801 wavelength channels over the 20 THz optical bandwidth.

The large number of wavelength channels were transmitted in each core of a 4-core MCF that is notable for having the same cladding diameter as a standard optical fiber. Such fibers are compatible with current cabling technologies and do not require the complex signal processing needed for unscrambling signals in multi-mode fibers, meaning conventional transceiver hardware may be used. 4-core MCFs are thought to be the most likely of the new advanced optical fibers for early commercial adoption. This demonstration shows their information carrying potential and is a significant step toward the realization of backbone communication systems that supports the evolution of Beyond 5G information services.

The results of this experiment were accepted as a post-deadline paper presentation at the International Conference on Laser and Electro-Optics (CLEO) 2022 and presented on Thursday, May 19, 2022.