In a groundbreaking advancement, researchers at the University of California, Irvine have innovated a method that transforms the interaction between light and matter. Their work has led to the creation of ultrathin silicon solar cells that hold promise for a wide array of applications, ranging from thermoelectric clothing to efficient onboard charging solutions for vehicles and portable devices.
The pivotal development, which has garnered attention as the cover story in the renowned journal ACS Nano, stems from the UC Irvine researchers’ successful conversion of conventional silicon into a direct bandgap semiconductor. This transformation significantly enhances its interaction with light, paving the way for improved energy conversion capabilities.
In partnership with scientists from Kazan Federal University in Russia and Tel Aviv University, the UC Irvine team adopted an innovative strategy that focuses on conditioning light rather than altering the silicon material itself. By strategically confining photons on sub-3-nanometer asperities located near the bulk semiconductor, they introduced a unique property of light — increased momentum. This expanded momentum unlocks novel interaction pathways between light and matter, thereby significantly enhancing light absorption. The researchers’ technique of “decorating” the silicon surface resulted in an exponential rise in device performance, bringing us closer to a new frontier in solar technology.
“In direct bandgap semiconductor materials, electrons transition from the valence band to the conduction band through a straightforward process that merely necessitates a change in energy; this leads to an efficient transfer,” remarked lead author Dmitry Fishman, who is also a UC Irvine adjunct professor of chemistry. “However, in the case of indirect bandgap materials like silicon, this transition requires the involvement of an additional component — a phonon — to provide the necessary momentum for the electron’s shift. Because the probability of a photon, phonon, and electron interacting simultaneously is quite low, silicon’s optical properties remain inherently weak.”
Silicon’s characteristics as an indirect bandgap semiconductor hinder progress in solar energy conversion technologies and the broader realm of optoelectronics. This is particularly disheartening given that silicon is the second-most abundant element in the Earth’s crust and serves as the cornerstone of the global computer and electronics industries.
Co-author Ara Apkarian, UC Irvine’s Distinguished Professor emeritus of chemistry, elaborated: “This phenomenon fundamentally alters our understanding of light’s interaction with matter. Conventional teaching emphasizes vertical optical transitions, wherein a material absorbs light and a photon solely alters an electron’s energy state. However, momentum-enhanced photons allow for changes in both energy and momentum states of the electrons, unveiling new transition pathways previously not considered. We can metaphorically ’tilt the textbook’ because these photons enable diagonal transitions which considerably improve a material’s capability to either absorb or emit light.”
The researchers foresee significant opportunities emerging from recent advancements in semiconductor fabrication techniques that operate at scales below 1.5 nanometers. Such innovations could have profound implications for photo-sensing technologies and the conversion of light energy.
“With the imminent effects of climate change, the transition from fossil fuels to renewable energy sources is more crucial than ever. Solar energy is a vital component of this shift, yet the commercial solar cells currently in use are failing to meet our needs,” Potma emphasized. “Silicon’s inherent limitations in light absorption necessitate the use of thick layers — approximately 200 micrometers of pure crystalline material — for adequate sunlight capture. This not only inflates production costs but also compromises efficiency due to increased charge carrier recombination. Our research brings thin-film solar cells one step closer to reality, which many regard as the solution to these pressing challenges.”
Other contributors to this significant study include Jovany Merham and Aleksey Noskov from UC Irvine; Elina Battalova and Sergey Kharintsev from Kazan Federal University; and Liat Katrivas and Alexander Kotlyar from Tel Aviv University. Financial backing for the project was generously provided by the Chan Zuckerberg Initiative.
**Interview with Dmitry Fishman, Lead Researcher on Ultrafine Silicon Solar Cells**
**Editor:** Thank you for joining us today, Dmitry. Your team’s recent work in transforming silicon into a direct bandgap semiconductor is groundbreaking. Can you explain to our audience what that means for silicon solar cells?
**Dmitry Fishman:** Thank you for having me! Essentially, silicon has been known as an indirect bandgap semiconductor, which means that it struggles with efficient light absorption because it requires an extra component—like a phonon—for electrons to transition from the valence band to the conduction band. By converting it into a direct bandgap semiconductor, we allow these electronic transitions to happen more straightforwardly, enhancing the interaction between silicon and light. This leads to significantly improved energy conversion capabilities.
**Editor:** That’s fascinating! You mentioned the need to condition light rather than changing the silicon itself. Can you elaborate on how that process works?
**Dmitry Fishman:** Certainly! Our approach involves using sub-3-nanometer asperities on silicon surfaces to confine photons. This confinement increases the momentum of the light, which opens up new pathways for interaction between light and the silicon material. By “decorating” the silicon surface with these features, we drastically improved the light absorption properties of silicon, leading to higher device performance.
**Editor:** The implications of your research could be substantial. What kinds of applications do you envision for these ultrathin solar cells?
**Dmitry Fishman:** We see immense potential for various applications, from thermoelectric clothing and efficient onboard charging solutions for electric vehicles to portable devices. Because our solar cells are ultrathin, they can be integrated into a range of surfaces without adding significant weight or bulk, making them extremely versatile.
**Editor:** Silicon is such a common element. How do you foresee your findings impacting the broader fields of solar energy conversion and optoelectronics?
**Dmitry Fishman:** Our findings could revolutionize these fields by improving the fundamental understanding of how light interacts with silicon. With this enhanced interaction, we may be able to unlock new technologies that capitalize on silicon’s abundance and utility, paving the way for more efficient solar technologies and innovative electronic devices.
**Editor:** That’s an exciting prospect! As this research progresses, what are the next steps for you and your team?
**Dmitry Fishman:** The immediate next steps involve refining these techniques and optimizing our processes for larger-scale production. We also want to collaborate further with industry partners to explore commercialization opportunities for these new solar cell technologies.
**Editor:** Thank you, Dmitry, for sharing your insights today. Your team’s work is certainly paving the way for the next generation of solar energy technology!
**Dmitry Fishman:** Thank you! It’s an exciting time in research, and we’re eager to see where this leads.
