The 5GSOLAR project develops environmentally friendly solar power to power indoor equipment.
Solar power has long been associated with rooftops, sunlight, and wide open skies. However, much of modern life takes place indoors, under office lights, kitchen lamps, and the soft light of the home. Our world is filled with small electronic devices that operate silently in the background, leading to the question: “Can solar energy be harnessed indoors?”
The answer is, of course, yes, and it may lie in a relatively simple, little-known, earth-abundant substance called antimony sulfide (Sb2S3).
Why indoor solar is important
Modern life is full of small devices that require constant power, such as 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 rely heavily on batteries.
Replacing and disposing of batteries is inconvenient, expensive, and environmentally harmful. Indoor solar cells offer an attractive alternative: devices that use light already around them to power themselves.
Indoor solar power generation – simply put, “the conversion of artificial light into electricity” – has become one of the most active and popular areas of solar research. Unlike outdoor solar panels, indoor solar cells do not need to generate large amounts of electricity. Instead, it must operate efficiently under low-power lighting.
Sb2S3-based indoor solar cells could help turn this vision into reality, allowing electronic devices to operate continuously without replacing batteries.
A rising star in indoor solar energy: The driving force for success
This is where Sb2S3 starts to stand out. Recent studies have shown that it is very suitable for collecting indoor light sources such as LEDs and fluorescent lights. As scientists search for practical materials for indoor energy harvesting, Sb2S3 has emerged as a promising candidate.
What makes Sb2S3 particularly attractive are its unique properties: it is environmentally friendly, abundant in the earth, and inherently stable. Unlike CdTe and lead-based perovskites, Sb2S3 avoids toxic and rare elements, making it a sustainable alternative for large-scale solar power generation. It has a bandgap of approximately 1.7–1.8 eV and a high absorption coefficient (approximately 105 cm-1), making it particularly suitable for indoor photovoltaic applications where traditional silicon devices have significantly reduced efficiency. Although the current outdoor efficiency (about 8.3%) is still lower than crystalline silicon (about 26%), Sb2S3 shows remarkable performance under low-intensity illumination and offers superior stability compared to perovskite absorbers. These properties position Sb2S3 as a promising candidate for indoor energy harvesting and IoT applications.
A glimpse inside the laboratory
Behind this technology is careful laboratory work. Research begins not with a finished product, but with a simple glass substrate and the step-by-step application of thin layers of material. Scientists adjust conditions, refine processing procedures, and test how small changes affect performance.
Controlled heating and precise deposition transform Sb2S3 from raw material into functional components that can convert light in a room into electricity.
Early but powerful technology
What makes this story particularly exciting is its freshness. The use of Sb2S3 for indoor photovoltaic applications is still in its infancy, and researchers are just beginning to uncover its full potential. Over the past decade, device efficiency has steadily increased from less than 3% for initial architectures under standard lighting to more than 8% for optimized thin-film structures, with even higher relative performance reported under indoor lighting conditions. Beyond efficiency gains, new features expand its appeal. Translucent Sb2S3 devices are being investigated for smart windows and building-integrated photovoltaics. The hope is that each experiment adds another piece to the puzzle, steadily opening the door to better designs and broader real-world adoption.
Sb2S3 powers the future! As buildings become smarter and devices become more connected, indoor solar cells could become an invisible but essential part of our environment. And behind its silent power source is a simple material refined in a lab that operates silently under indoor light.
Part of that future is taking shape in our lab today, as we discover new ways to unlock the full potential of this material. Want to learn more? You can explore the complete scientific research behind this research in a recently published paper.
Acknowledgment
This project is funded by the European Union’s Horizon 2020 research.
This research was also funded by the Estonian Research Council project PRG2676.
Please note: This is a commercial profile
This article will also be published in the quarterly magazine issue 25.
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