| Work Detail |
An international team led by the U.S. National Renewable Energy Laboratory (NREL) has used ionic salt for the electron transport layer of a perovskite solar cell to improve the devices stability and performance. Test results showed a power conversion efficiency of 26% with a 2% degradation after 2,100 hours of operation under 1 sun at 65°C. An international team led by the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) has applied a novel ionic salt to the electron transport layer (ETL) interface of flipped perovskite solar cells to overcome the weaknesses of commonly used optimized buckminsterfullerene (C60) ETLs. Inverted perovskite cells have a device structure known as pin, in which the hole-selective contact p is located on the bottom of the intrinsic perovskite layer (i) with the electron transport layer (n) on the top. Conventional halide perovskite cells have the same structure but inverted: a nip arrangement. In the nip architecture, the solar cell is illuminated through the electron transport layer (ETL) side; in the pin structure, it is illuminated through the HTL surface. “One of the major problems with conventional device stacks is the weak interface between the perovskite absorber layer and the ETL,” Kai Zhu, corresponding author of the research, told pv magazine . To solve this problem, the researchers developed an ionic salt synthesized from C60, dubbed CPMAC in the study. The acronym CPMAC stands for N-methylglycine, tert-butyl 4-formylbenzylcarbamate, and hydrochloric acid molecules. It reacts with C60 to form an ionic salt called 4-(1'',5''-dihydro-1''-methyl-2''H-[5,6]fullerene-C60-Ih-[1,9-c]pyrrol-2''-yl)phenylmethanaminium chloride. We are very pleased that our new CPMAC ionic salt can significantly strengthen this interface by a factor of three, without adversely affecting device performance, Zhu says. In the study, the researchers used CPMAC salt as an electron shuttle in flipped perovskite solar cells (PSCs) and minimodules. This ionic salt layer fundamentally addressed the disadvantages of the C60 molecular layer, the researchers noted. Test results for the non-encapsulated perovskite solar cell with CPMAC showed a power conversion efficiency (PCE) of 26%, with a 2% degradation after 2,100 hours of standard operation at 1 sun at 65°C. The PSC had an efficiency of 25.5%, with a degradation of approximately 5% after 1,500 hours of operation at 85°C. The 6 cm2 mini-modules achieved a PCE of 23% with less than 9% degradation after 2,200 hours of operation at 55°C, according to the research. The work is described in “ C60 -based ionic salt electron shuttle for high-performance inverted perovskite solar modules,” published in Science . The team included researchers from CubicPV, the University of Colorado at Boulder, Arizona State University, and the University of Toledo, all based in the United States, as well as King Abdullah University of Science and Technology in Saudi Arabia and Newcastle University in the United Kingdom. The scientists plan to explore the potential of solution deposition based on the research results. “This CPMAC layer can be deposited using solution processing, which is attractive for large-scale manufacturing. We plan to further develop solution processing conditions and integrate this new material into large-scale module platforms,” Zhu said. |
