New insight into how a certain class of photovoltaic materials allows efficient conversion of sunlight into electricity could set up these materials to replace traditional silicon solar cells. A study by researchers at Penn State reveals the unique properties of these inexpensive and quick-to-produce halide perovskites, information that will guide the development of next generation solar cells. The study appears September 27 in the journal Chem.

“Since the development of silicon solar cells, which today can be found on rooftops and roadsides, researchers have sought new types of photovoltaic materials that are easier to process into solar cells,” said John Asbury, associate professor of chemistry at Penn State and senior author of the study. “This is because construction of silicon solar cells is complex and hard to scale-up to the level that would be needed for them to generate even 10 percent of our total demand for electricity.”

Because of these complications, researchers have been searching for less expensive alternatives to silicon solar cells that can be processed more quickly. They are particularly interested in materials that can be processed using a technique called roll-to-roll manufacturing, a technique similar to those used to print newspapers that enables low-cost, high-volume production. Such materials must be processed from solution, like ink printed on a page.

Scientists in the United States and Saudi Arabia have harnessed the abilities of both a solar cell and a battery in one device—a “solar flow battery” that soaks up sunlight and efficiently stores it as chemical energy for later on-demand use. Their research, published September 27 in the journal Chem, could make electricity more accessible in remote regions of the world.

While sunlight has increasingly gained appeal as a clean and abundant energy source, it has one obvious limitation—there is only so much sunlight per day, and some days are a lot sunnier than others. In order to keep solar energy practical, this means that after sunlight is converted to electrical energy, it must be stored. Normally this takes two devices—a solar cell and a battery—but the solar flow battery is designed to perform like both.

“Compared with separated solar energy conversion and electrochemical energy storage devices, combining the functions of separated devices into a single, integrated device could be a more efficient, scalable, compact, and cost-effective approach to utilizing solar energy,” says Song Jin, a professor of chemistry at the University of Wisconsin-Madison. Jin and his team developed the device in collaboration with Jr-Hau He, a professor of electrical engineering at King Abdullah University of Science and Technology (KAUST) in Saudi Arabia.

At today’s EU PVSEC conference, imec—the world-leading research and innovation hub in nanoelectronics, energy and digital technology and partner in EnergyVille—announced that its latest generation of large-area monofacial screen-printed rear-emitter nPERT cells feature a conversion efficiency of 23.03 percent, certified by Fraunhofer ISE CalLab. The nPERT (n-type Passivated Emitter and Rear Totally diffused) solar cells are made using an industry-compatible screen-printing process that has been designed as an upgrade of conventional pPERC (p-type Passivated Emitter and Rear Cell) processes. According to imec, its nPERT technology is projected to reach 23.5 percent efficiency by the end of this year, and there is a clear technology roadmap to eventually surpass 24 percent.

While p-type PERC solar cells are becoming mainstream in the PV industry, n-type PERT technology is being developed as a cost-effective contender that has a number of inherent advantages: Due to the absence of B-O complexes, n-type cells don’t suffer from light induced degradation (LID) and are less sensitive to metal impurities. That makes for cells that have the potential for a longer-term stability and a higher efficiency. Imec fabricated the M2-sized cells (area: 244.3 cm²) on its pilot line with industry-compatible tools and recipes, in a process that is an upgrade of the pPERC fabrication process, using a similar layout of an n+ region (Front Surface Field) on the illuminated side and a p+ region (as rear emitter) on the opposite side and adding a cost-effective boron diffusion.

“Until now, nPERT solar technology has not yet found the traction it deserves in the industry,” says Loic Tous, senior researcher at imec. “With these ever-improving results, which we achieved by applying knowledge gained from our bifacial nPERT project, we are now demonstrating the potential of nPERT technology. The advantages in stability and efficiency potential over p-type PERC cells, while using the same equipment with the addition of a Boron diffusion, make this a very promising technology for future manufacturing lines.”