Solar power has long been associated with rooftops, sunlight, and wide-open skies. Yet, much of modern life happens indoors, under office lights, kitchen lamps, and the soft glow of our homes. As our world fills with small electronic devices that quietly work in the background, the question is: ‘Can solar energy work indoors too?’
The answer is yes of course, and it may lie in a relatively simple and little-known Earth-abundant material called antimony sulfide (Sb2S3).
Modern life is filled with small devices that need constant power: smart sensors that monitor air quality, wearable health devices, electronic labels, and Internet of Things (IoT) systems embedded in homes and workplaces. These devices consume very little energy, but they rely heavily on batteries.
Replacing and disposing of batteries is inconvenient, costly, and environmentally harmful. Indoor solar cells offer a compelling alternative: devices that power themselves using the light already around them.
Indoor photovoltaics – in simple terms, ‘the conversion of artificial light into electricity’ – have become one of the most active and popular areas in solar research. Unlike outdoor solar panels, indoor solar cells don’t need to generate large amounts of power. Instead, they must work efficiently under low-power lighting.
Sb2S3-based indoor solar cells could help make this vision practical, enabling electronics that operate continuously without battery replacement.
This is where Sb2S3 has begun to stand out. Recent research shows that it is very well suited to harvest indoor light sources such as LEDs and fluorescent lamps. At a time when scientists are searching for practical materials for indoor energy harvesting, Sb2S3 is emerging as a promising candidate.
What makes Sb2S3 particularly compelling is its unique nature, being environmentally friendly, Earth abundant, and intrinsically stable. Unlike CdTe or lead-based perovskites, Sb2S3 avoids toxic or scarce elements, making it a sustainable alternative for large-scale photovoltaics. With a bandgap of ~1.7–1.8 eV and a high absorption coefficient (~10⁵ cm-1), it is especially well suited for indoor photovoltaic applications, where conventional silicon devices suffer significant efficiency losses. While its current outdoor efficiency (~8.3%) remains below that of crystalline silicon (~26%), Sb2S3 demonstrates remarkable performance under low-intensity illumination and offers great stability compared to perovskite absorbers. These attributes position Sb2S3 as a promising candidate for indoor energy harvesting and IoT applications.
Behind this technology lies careful laboratory work. Research does not begin with finished products, but with simple glass substrates and thin layers of material applied step by step. Scientists adjust conditions, refine processing steps, and test how small changes affect performance.
Through controlled heating and precise layering, Sb2S3 is transformed from a raw material into a functional component capable of converting indoor light into electricity.
What makes this story especially exciting is its freshness. The use of Sb2S3 for indoor solar applications is still emerging, and researchers are only beginning to uncover its full potential. Over the past decade, device efficiencies have steadily improved from below 3% in early architectures to over 8% in optimised thin-film structures under standard illumination, with even higher relative performance reported under indoor lighting conditions. Beyond efficiency gains, new features are expanding its appeal. Semi-transparent Sb2S3 devices are being explored for smart windows and building-integrated photovoltaics. Promisingly, each experiment adds another piece to the puzzle, steadily opening doors to better designs and broader real-world adoption.
Sb2S3 is powering the future! As buildings become smarter and devices more connected, indoor solar cells could become an unseen but essential part of our environment. And somewhere behind that quiet power source will be a simple material, refined in the lab, now working silently under indoor light.
Part of that future is taking shape today in our laboratory, where we are uncovering new ways to unlock the full potential of this material. Curious to learn more? You can explore the full scientific study behind this work in our recently published paper.
This project has received funding from the European Union’s Horizon 2020 research and
innovation programme under grant agreement No 952509. The research has also received funding from the Estonian Research Council Project PRG2676.
Please note, this article will also appear in the 25th edition of our quarterly publication.
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