Stacking perovskites onto a conventional silicon solar cell dramatically improves the overall efficiency of the cell, according to a new study led by Stanford University scientists.
The researchers describe their novel perovskite-silicon solar cell in this week's edition of the journal Energy & Environmental Science.
"We've been looking for ways to make solar panels that are more efficient and lower cost," said study co-author Michael McGehee, a professor of materials science and engineering at Stanford. "Right now, silicon solar cells dominate the world market, but the power conversion efficiency of silicon photovoltaics has been stuck at 25 percent for 15 years."
One cost-effective way to improve efficiency is to build a tandem device made of silicon and another inexpensive photovoltaic material, he said.
"Making low-cost tandems is very desirable," McGehee said. "You simply put one solar cell on top of the other, and you get more efficiency than either could do by itself. From a commercial standpoint, it makes a lot of sense to use silicon for the bottom cell. Until recently, we didn't have a good material for the top cell, then pervoskites came along."
Perovskite is a crystalline material that is inexpensive and easy to produce in the lab. In 2009, scientists showed that perovskites made of lead, iodide and methylammonium could convert sunlight into electricity with an efficiency of 3.8 percent. Since then, researchers have achieved perovskite efficiencies above 20 percent, rivaling commercially available silicon solar cells and spawning widespread interest among silicon manufacturers.
"Our goal is to leverage the silicon factories that already exist around the world," said Stanford graduate student Colin Bailie, co-lead author of the study. "With tandem solar cells, you don't need a billion-dollar capital expenditure to build a new factory. Instead, you can start with a silicon module and add a layer of perovskite at relatively low cost."
Sunlight to electricity
Solar cells work by converting photons of sunlight into an electric current that moves between two electrodes. Silicon solar cells generate electricity by absorbing photons of visible and infrared light, while perovskite cells harvest only the visible part of the solar spectrum where the photons have more energy.
"Absorbing the high-energy part of the spectrum allows perovskite solar cells to generate more power per photon of visible light than silicon cells," Bailie said.
A key roadblock to building an efficient perovskite-silicon tandem has been a lack of transparency.
"Colin had to figure out how to put a transparent electrode on the top so that some photons could penetrate the perovskite layer and be absorbed by the silicon at the bottom," McGehee said. "No one had ever made a perovskite solar cell with two transparent electrodes."
Perovskites are easily damaged by heat and readily dissolve in water. This inherent instability ruled out virtually all of the conventional techniques for applying electrodes onto the perovoskite solar cell, so Bailie did it manually.
"We used a sheet of plastic with silver nanowires on it," he said. "Then we built a tool that uses pressure to transfer the nanowires onto the perovskite cell, kind of like a temporary tattoo. You just need to rub it to transfer the film."
For the experiment, the Stanford team stacked a perovskite solar cell with an efficiency of a 12.7 percent on top of a low-quality silicon cell with an efficiency of just 11.4 percent.
"By combining two cells with approximately the same efficiency, you can get a very large efficiency boost," Bailie said.
The results were impressive.
"We improved the 11.4 percent silicon cell to 17 percent as a tandem, a remarkable relative efficiency increase of nearly 50 percent," McGehee said. "Such a drastic improvement in efficiency has the potential to redefine the commercial viability of low-quality silicon."
In another experiment, the research team replaced the silicon solar cell with a cell made of copper indium gallium diselenide (CIGS). The researchers stacked a 12.7 percent efficiency perovskite cell onto a CIGS cell with a 17 percent efficiency. The resulting tandem achieved an overall conversion efficiency of 18.6 percent.
"Since most, if not all, of the layers in a perovskite cell can be deposited from solution, it might be possible to upgrade conventional solar cells into higher-performing tandems with little increase in cost," the authors wrote.
A big unanswered question is the long-term stability of perovskites, McGehee added.
"Silicon is a rock," he said. "You can heat it to about 600 degrees Fahrenheit shine light on it for 25 years and nothing will happen. But if you expose perovskite to water or light it likely will degrade. We have a ways to go to show that perovskite solar cells are stable enough to last 25 years. My vision is that some day we'll be able to get low-cost tandems that are 25 percent efficient. That's what companies are excited about. In five to 10 years, we could even reach 30 percent efficiency."
The study was also written by co-lead author M. Greyson Christoforo, Andrea Bowring, Eva Unger, William Nguyen and Alberto Salleo from Stanford; Jonathan Mailoa, Jungwoo Lee and Tonio Buonassisi from the Massachusetts Institute of Technology; Julian Burschka, Norman Pellet and Michael Graetzel from the Swiss École Polytechnique Fédérale de Lausanne; and Rommel Noufi, formerly with the U.S. National Renewable Energy Laboratory.
This article was written by Mark Shwartz, Precourt Institute for Energy at Stanford University.
Mark Shwartz | EurekAlert!
Neutrons pave the way to accelerated production of lithium-ion cells
20.03.2018 | Technische Universität München
Monocrystalline silicon thin film for cost-cutting solar cells with 10-times faster growth rate fabricated
16.03.2018 | Tokyo Institute of Technology
An international team of researchers has discovered a new anti-cancer protein. The protein, called LHPP, prevents the uncontrolled proliferation of cancer cells in the liver. The researchers led by Prof. Michael N. Hall from the Biozentrum, University of Basel, report in “Nature” that LHPP can also serve as a biomarker for the diagnosis and prognosis of liver cancer.
The incidence of liver cancer, also known as hepatocellular carcinoma, is steadily increasing. In the last twenty years, the number of cases has almost doubled...
In just a few weeks from now, the Chinese space station Tiangong-1 will re-enter the Earth's atmosphere where it will to a large extent burn up. It is possible that some debris will reach the Earth's surface. Tiangong-1 is orbiting the Earth uncontrolled at a speed of approx. 29,000 km/h.Currently the prognosis relating to the time of impact currently lies within a window of several days. The scientists at Fraunhofer FHR have already been monitoring Tiangong-1 for a number of weeks with their TIRA system, one of the most powerful space observation radars in the world, with a view to supporting the German Space Situational Awareness Center and the ESA with their re-entry forecasts.
Following the loss of radio contact with Tiangong-1 in 2016 and due to the low orbital height, it is now inevitable that the Chinese space station will...
Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology FEP, provider of research and development services for OLED lighting solutions, announces the founding of the “OLED Licht Forum” and presents latest OLED design and lighting solutions during light+building, from March 18th – 23rd, 2018 in Frankfurt a.M./Germany, at booth no. F91 in Hall 4.0.
They are united in their passion for OLED (organic light emitting diodes) lighting with all of its unique facets and application possibilities. Thus experts in...
A new scenario seeking to explain how Mars' putative oceans came and went over the last 4 billion years implies that the oceans formed several hundred million...
For the first time, an interdisciplinary team from the University of Basel has succeeded in integrating artificial organelles into the cells of live zebrafish embryos. This innovative approach using artificial organelles as cellular implants offers new potential in treating a range of diseases, as the authors report in an article published in Nature Communications.
In the cells of higher organisms, organelles such as the nucleus or mitochondria perform a range of complex functions necessary for life. In the networks of...
19.03.2018 | Event News
16.03.2018 | Event News
13.03.2018 | Event News
22.03.2018 | Trade Fair News
22.03.2018 | Earth Sciences
22.03.2018 | Earth Sciences