Material discoveries signal bright future for solar cells
Halide perovskites are a class of semiconductor material that when used in a solar cell can turn sunlight into electricity (and electricity into visible light in LEDs). While the material has been known about for several decades, its tremendous potential for photovoltaics (solar cells) has only recently been realised. “Compared to standard semiconductor material like silicon, halide perovskites have several advantages,” explains Henk Bolink, professor at the Institute of Molecular Science, University of Valencia, Spain. “High-quality perovskites can be formed through extremely simple chemical processes. The material can then be made to span the whole visible range, from the infrared to the ultraviolet. This opens up a range of possible applications, such as solar cells and white LEDs.” A key challenge in commercialising this material however has been economic viability. Large-scale photovoltaic devices need operational lifetimes of at least 10 years, while state-of-the-art LEDs operate for thousands of hours. “Improvements in the stability of perovskite-based photovoltaic and LEDs are needed,” says Bolink. A second challenge is that all high-efficiency halide perovskite solar cells and LEDs contain small amounts of toxic lead. Lead-free perovskites would remove the need for containment and recycling. Achieving solvent-free processing would make perovskite an even more attractive proposition.
Low-toxic alternatives
The PerovSAMs project was launched in January 2018 to explore low-toxic alternative materials to lead halide perovskites, and to develop solvent-free production methods. This research involved Francisco Palazon as the grantee of the Individual Fellowships of the Marie Skłodowska-Curie Actions programme. “Sometimes the simplest ideas are the best,” says Bolink. “Before starting, we didn't really think that grinding chemicals together could lead to the formation of so many interesting materials. However, we began to see great potential in this technique.” The project team explored different chemical compositions. “The quest for replacing lead with more environmentally friendly metals took us to more ‘exotic’ materials, such as ternary copper halides,” adds Bolink. A key challenge was turning powder materials into thin films (as one might find in devices such as solar cells). A technique to heat powder inside a vacuum chamber was developed, in order to condense materials into a desired substrate. “We also found, to our surprise, that high-quality pellets, which could be interesting for X-ray detectors, could be prepared simply from pressing the powders,” explains Bolink.
Potential for industry
The success of the PerovSAMs project in developing a vacuum-based production process, as well as producing low-toxic copper halides with bright blue luminescence, has been shared in academic journals. “The technology developed in this project has great potential for transfer to industry,” notes Bolink. “We are now optimising the processes to allow for upscaling production.” This project has also kick-started a new line of research into halide perovskites and related optoelectronics. “We expect that the techniques we applied will become more and more widely adopted,” says Bolink. “This will help in the discovery of new materials and their implementation in photovoltaics and other applications.” The rapid development of perovskite compositions is one of the starting points of the ERC-funded project HELD, for which Bolink is the principal investigator. The project started in September 2019, and aims to develop highly luminescent multilayer stacks and reproducible production methods. “Here, we will further develop the methods pioneered in PerovSAMs, turning powders into homogenous thin films,” he concludes.
Keywords
PerovSAMs, Halide perovskites, solar, LED, photovoltaic, toxic, luminescent, optoelectronics, solvent-free, chemical
