19 February 2020
A touch of alkylamine helps perovskites grab energy from the sun
Published online 23 January 2020
Trace amounts of organic amine molecules on perovskites coax their assembly into better films for solar cells.
Adding long-chain alkylamines – carbon-based molecules with amine groups attached – improves the performance of perovskites, providing promise for the development of the next generation of solar cells.
Scientists at King Abdullah University of Science and Technology in Saudi Arabia (KAUST) are using the modification to achieve impressive efficiency enhancements with unconventional ‘inverted’ solar cells.
Synthetic and semiconducting metal halide perovskites have a chemical formula of ABX3, where A and B stand for positively charged ‘cations’ of different size and X represents negatively charged halide ‘anions’.
“Various metal halide perovskites have cemented their place as key components of next-generation solar cells,” says KAUST materials scientist Osman M. Bakr.
Perovskite solar cells are expected to improve the efficiency and reduce the costs of solar energy, but challenges remain as they decay relatively quickly. The solar cells are formed of a perovskite layer sandwiched between layers of other materials that transfer electrons kicked from the perovskite in one direction, while ‘holes’ deficient in electrons move in the other direction. Light energy hitting the perovskite keeps these changes going, generating an electric current.
Conventional and ‘inverted’ solar cell architectures differ in the sequence in which the component layers are arranged. Bakr explains that inverted perovskite solar cells are attracting increasing attention because they can have longer operating lifetimes and greater stability. Until now, however, they have yielded significantly inferior power conversion efficiencies compared to those with the conventional architecture.
The KAUST researchers, with collaborators in Canada and Sweden, found that alkylamines added to the perovskite-forming solution attach to the surfaces of perovskite crystal grains. This modifies the grains’ arrangement and their interactions, overcoming key limitations of previous inverted solar cells.
“It was surprising to discover that only a trace amount of alkylamine was enough to create a surface layer on the perovskite film that improved its properties in such significant ways,” Bakr says.
In addition to an impressive power conversion efficiency of more than 22 percent, the devices are significantly more stable than previously achieved without the alkylamine assistance. In lab tests, they operated for more than 1,000 hours without any decline in performance.
Despite the great interest in perovskite solar cells, they have largely remained in the research phase due to efficiency and stability issues that are limiting their commercial exploitation.
“Only by closing this efficiency-stability gap will we get perovskite solar cells to deliver on their promise to make real industrial and environmental impacts,” says Bakr.
Zheng, X. et al. Managing grains and interfaces via ligand anchoring enables 22.3%-efficiency inverted perovskite solar cells. Nat. Energy https://doi.org/10.1038/s41560-019-0538-4 (2020).