Major leap for stable high-efficiency perovskite solar cells
Ion-modulated radical doping of spiro-OMeTAD for more efficient and stable perovskite solar cells
Peer-Reviewed PublicationIMAGE: FENG WANG, JUNIOR LECTURER AT LINKÖPING UNIVERSITY. view more
CREDIT: ANNA NILSEN
Solar cells manufactured from materials known as “perovskites” are catching up with the efficiency of traditional silicon-based solar cells. At the same time, they have advantages of low cost and short energy payback time. However, such solar cells have problems with stability – something that researchers at Linköping University, together with international collaborators, have now managed to solve. The results, published in Science, are a major step forwards in the quest for next-generation solar cells.
“Our results open new possibilities to develop efficient and stable solar cells. Further, they provide new insights into how the doping of organic semiconductors works,” says Feng Gao, professor in the Department of Physics, Chemistry and Biology (IFM) at Linköping University.
Perovskites are crystalline materials with huge potential to contribute to solving the world’s energy shortage. They are cheap to manufacture, with high efficiency and low weight. However, the perovskite solar cells can degrade quickly, and it has not been possible to build high-efficiency perovskite-based solar cells with the required stability.
“There seems to be a trade-off between high efficiency and stability in perovskite-based solar cells. High-efficiency perovskite solar cells tend to show low stability, and vice versa,” says Tiankai Zhang, a postdoc at IFM and one of the principal authors of the article published in Science.
When solar energy is converted into electricity in perovskite-based solar cells, one or more charge transport layers are usually needed. These lie directly next to the perovskite layer in the solar cell. The organic charge transport layers often need auxiliary molecules in order to function as intended. The material is described as being “doped”.
One doped transport layer called Spiro-OMeTAD is a benchmark in perovskite solar cells, and delivers record power conversion efficiencies. But the present method used to dope Spiro-OMeTAD is slow, and causes the stability issue of perovskite solar cells.
“We have now managed to eliminate the trade-off that has hindered development, using a new doping strategy for Spiro-OMeTAD. This makes it possible for us to obtain both high efficiency and good stability,” says Tiankai Zhang.
Another principal author of the article, Feng Wang, is a junior lecturer at IFM. He points out that perovskite-based solar cells can be used in many ways, and have many areas of applications.
“One advantage of using perovskites is that the solar cells made are thin, which means that they are light and flexible. They can also be semi-transparent. It would be possible, for example, to apply perovskite-based solar cells onto large windows, or building façades. Silicon-based solar cells are too heavy to be used in this way,” says Feng Wang.
The study has been financed by the Swedish Research Council, an ERC Starting Grant, the Knut and Alice Wallenberg Foundation and AFM (the Swedish Government Strategic Research Area in Materials Science on Functional Materials) at Linköping University. Feng Gao is also a Wallenberg Academy Fellow.
CAPTION
Solar cells manufactured from materials known as “perovskites” are catching up with the efficiency of traditional silicon-based solar cells.
CREDIT
Anna Nilsen
JOURNAL
Science
ARTICLE TITLE
Ion-modulated radical doping of spiro-OMeTAD for more efficient and stable perovskite solar cells
NREL-led breakthrough pushes perovskite cell to greater stability, efficiency
Researchers at the U.S. Department of Energy’s (DOE’s) National Renewable Energy Laboratory (NREL) made a technological breakthrough and constructed a perovskite solar cell with the dual benefits of being both highly efficient and highly stable.
The work was done in collaboration with scientists from the University of Toledo, the University of Colorado–Boulder, and the University of California–San Diego.
A unique architectural structure enabled the researchers to record a certified stabilized efficiency of 24% under 1-sun illumination, making it the highest reported of its kind. The highly efficient cell also retained 87% of its original efficiency after 2,400 hours of operation at 55 degrees Celsius.
The paper, “Surface Reaction for Efficient and Stable Inverted Perovskite Solar Cells,” appears in the journal Nature. The authors from NREL are Qi Jiang, Jinhui Tong, Ross Kerner, Sean Dunfield, Chuanxiao Xiao, Rebecca Scheidt, Darius Kuciauskas, Matthew Hautzinger, Robert Tirawat, Matthew Beard, Joseph Berry, Bryon Larson, and Kai Zhu.
Perovskite, which refers to a crystalline structure, has emerged in the last decade as an impressive means to efficiently capture sunlight and convert it to electricity. Research into perovskite solar cells has been focused to a large degree on how to increase their stability.
“Some people can demonstrate perovskites with high stability, but efficiency is lower,” said Zhu, a senior scientist in the Chemistry and Nanoscience Center at NREL. “You ought to have high efficiency and high stability simultaneously. That’s challenging.”
The researchers used an inverted architecture, rather than the “normal” architecture that has to date yielded the highest efficiencies. The difference between the two types is defined by how the layers are deposited on the glass substrate. The inverted perovskite architecture is known for its high stability and integration into tandem solar cells. The NREL-led team also added a new molecule, 3-(Aminomethyl) pyridine (3-APy), to the surface of the perovskite. The molecule reacted to the formamidinium within the perovskite to create an electric field on the surface of the perovskite layer.
“That suddenly gave us a huge boost of not only efficiency but also stability,” Zhu said.
The scientists reported the 3-APy reactive surface engineering can improve the efficiency of an inverted cell from less than 23% to greater than 25%. They also noted the reactive surface engineering stands out as an effective approach to significantly enhance the performance of inverted cells “to new state-of-the-art levels of efficiency and operational reliability.”
Funding for the research done at NREL came from the Center for Hybrid Organic-Inorganic Semiconductors for Energy (CHOISE), an Energy Frontier Research Center within DOE’s Office of Basic Energy Sciences, and from the DOE’s Solar Energy Technologies Office.
NREL is the U.S. Department of Energy's primary national laboratory for renewable energy and energy efficiency research and development. NREL is operated for the Energy Department by the Alliance for Sustainable Energy, LLC.
JOURNAL
Nature
METHOD OF RESEARCH
Experimental study
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
Surface reaction for efficient and stable inverted perovskite solar cells
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