By james art Irvine, California, October 31, 2024 — By creating a new way for light and matter to interact, UC Irvine researchers have enabled the fabrication of ultrathin silicon solar cells that could help spread the energy conversion technology to a wide range of applications, including thermoelectric clothing and onboard vehicles means and charging devices.
The development, the subject of an article recently published as a cover story in the magazine ACS Nanodepends on the UC Irvine researchers converting pure silicon from an indirect to a direct bandgap semiconductor through the way it interacts with light.
The UC Irvine team, in collaboration with scientists from Russia’s Kazan Federal University and Tel Aviv University, explored an innovative approach by conditioning the light instead of changing the material itself. They confined photons onto sub-3 nanometer bumps near the bulk semiconductor, giving light a new property—broadened momentum—that opens up new pathways for interaction between light and matter. By “decorating” the silicon surface, the researchers said, they achieved an order-of-magnitude increase in light absorption, along with a significant increase in device performance.
“In semiconductor materials with a direct band gap, electrons move from the valence band to the conduction band. This process requires only a change of energy; it’s an efficient transfer,” notes lead author Dmitry Fishman, assistant professor of chemistry at UC Irvine. “In materials with an indirect bandgap such as silicon, an additional component – a phonon – is needed to provide the electron with the momentum needed to make the transition. Because the probability of a photon, phonon, and electron interacting at the same place and time is low, the optical properties of silicon are inherently weak.
He said that as an indirect semiconductor with a band gap, silicon’s poor optical properties have limited the development of solar energy conversion and optoelectronics in general, which is a disadvantage given that silicon is the second most abundant element in the Earth’s crust and core. , upon which the world’s computer and electronics industries were built.
“Photons carry energy but almost no momentum, but if we change this narrative explained in textbooks and somehow give photons momentum, we can excite electrons without needing extra particles,” said co-author Eric Potma, professor of chemistry at UC Irvine. “This reduces the interaction to just two particles, a photon and an electron, similar to what happens in semiconductors with a direct band gap, and increases light absorption by a factor of 10,000, completely transforming the light-matter interaction without changing the chemistry of the material itself. “
Co-author Ara Apkarian, professor emeritus of chemistry at UC Irvine, said: “This phenomenon fundamentally changes the way light interacts with matter. Traditionally, textbooks teach us about so-called vertical optical transitions, where a material absorbs light, with the photon changing only the energy state of the electron. Momentum-boosted photons, however, can change both the energy and momentum states of electrons, unlocking new transition pathways we hadn’t considered before. Figuratively speaking, we can “tilt the textbook” because these photons allow diagonal transitions. This dramatically affects the material’s ability to absorb or emit light.
According to the researchers, the development enables the use of recent advances in semiconductor fabrication techniques at the sub-1.5 nanometer scale, which has the potential to impact photosensing and light energy conversion technologies.
“With the escalating effects of climate change, it is more urgent than ever to switch from fossil fuels to renewable energy.” Solar energy is key in this transition, but the commercial solar cells we rely on are falling short,” Potma said. “Silicon’s poor ability to absorb light means these cells require thick layers – almost 200 micrometers of pure crystalline material – to effectively capture sunlight. This not only increases production costs, but also limits efficiency due to increased recombination of charge carriers. Thin-film solar cells, which are one step closer to reality thanks to our research, are seen as a solution to these challenges.”
Other co-authors of this study include Jovany Merham and Aleksey Noskov of UC Irvine; Kazan Federal University researchers Elina Batalova and Sergey Harintsev; and Tel Aviv University researchers Liat Katrivas and Alexander Kotlyar. The project received financial support from the Chan Zuckerberg Initiative.
About the University of California, Irvine: Founded in 1965, UC Irvine is a member of the prestigious Association of American Universities and is ranked among the nation’s top 10 public universities by US News and World Report. The campus has produced five Nobel laureates and is known for its academic excellence, world-class research, innovation and mascot anteater. Led by Chancellor Howard Gilman, UC Irvine has more than 36,000 students and offers 224 degree programs. Located in one of the safest and most economically vibrant communities in the world, it is the second largest employer in Orange County, contributing $7 billion annually to the local economy and $8 billion to the statewide economy. For more information about UC Irvine, visit www.uci.edu.
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