Lithuanian chemists found a way to harvest the “wasted” glow of a light bulb and turn it into electricity for smart devices
Every day, billions of light bulbs, LED panels, and phone screens pour light into rooms — and almost none of that energy is ever captured. It simply vanishes into walls, furniture, and air. In principle, the glow already surrounding us could power the small devices we carry and the sensors embedded in our homes. In a chemistry lab at Kaunas University of Technology in Lithuania, researchers have been working on exactly that problem: intercepting indoor light before it disappears for good.
The energy hiding in plain sight
Most conversations about renewable energy focus on rooftops, wind farms, and open fields. Indoor light rarely enters the picture. Yet every lamp, LED panel, and window that lets daylight in radiates energy that simply goes to waste. Professor Juozas Vidas Gražulevičius, who heads the Chemistry of Materials research group at KTU, puts it plainly: the energy from indoor light sources and natural light entering through windows is lost every day.
Wind and hydropower can address part of the clean energy challenge, but both come with real constraints — geography and infrastructure. Solar energy is more flexible, yet conventional photovoltaic systems are designed almost exclusively for outdoor sunlight. The indoor environment, where people spend most of their waking hours, has remained largely untapped. Indoor photovoltaics aim to close that gap, generating electricity under low-intensity artificial light — the kind filling every office, living room, and hospital corridor worldwide.
That test fell to researchers at Ming Chi University of Technology in Taiwan, who used the KTU-developed material to build perovskite solar cells for indoor use.
A market quietly waiting to be filled
The Internet of Things — the sprawling network of sensors, trackers, wearables, and connected appliances — is expanding rapidly. All of those devices need power. Batteries work, but they run out, require replacement, and create waste. A small photovoltaic cell harvesting ambient light could offer a cleaner, longer-lasting alternative.
Dr. Asta Dabulienė, a Senior Researcher at KTU, sees a concrete opportunity. Perovskite photovoltaic cells for indoor use could be integrated into mobile phones, pocket flashlights, and other consumer electronics. Using IoT infrastructure, the electricity they generate could help regulate device operation and cut overall energy consumption. The challenge is meeting high performance, low cost, and versatility all at once — exactly what the KTU team set out to address.
The molecule that makes it work
The core of the KTU breakthrough is a new series of chemical compounds — thiazol[5,4-d]thiazole derivatives — synthesized by Dr. Dabulienė specifically as hole-transporting materials in perovskite solar cells.
Inside a solar cell, light knocks electrons loose from atoms, creating charge pairs: a free electron and a positively charged “hole.” For the cell to produce useful electricity, these charges must travel in opposite directions without recombining. A hole-transporting layer guides positive charges toward one electrode while blocking negative ones from going the wrong way. When that separation works cleanly, energy losses drop and efficiency climbs.
An ideal hole-transporting semiconductor, Dr. Dabulienė explains, needs high hole mobility and precise energy-level alignment with surrounding layers. The thiazol[5,4-d]thiazole derivatives she synthesized were designed from the ground up to satisfy both.
37% efficiency under a light bulb
Synthesizing a promising compound is one thing. Proving it works inside a real device is another. That test fell to researchers at Ming Chi University of Technology in Taiwan, who used the KTU-developed material to build perovskite solar cells for indoor use.
The results were notable. Under 3000 K LED illumination at 1000 lux — roughly the brightness of a well-lit office — the cells achieved a power conversion efficiency of 37.0%. Indoor photovoltaic cells have historically struggled to reach commercially viable efficiency levels, so this figure represents a meaningful step forward. It validates thiazol[5,4-d]thiazole derivatives as a credible platform for next-generation indoor photovoltaics, not just a laboratory curiosity.
Science without borders: how the breakthrough came together
No single institution could have produced this result alone. The innovation emerged from a collaboration spanning three continents. KTU synthesized and characterized the organic semiconductors. Scientists at King Abdullah University of Science and Technology in Saudi Arabia ran the theoretical modeling, while Ming Chi University of Technology in Taiwan built and tested the cells.
Professor Gražulevičius acknowledges that international teamwork brings real challenges — communication gaps, cultural differences, organizational complexity. But the benefits are just as tangible. Different cultures and experiences generate ideas no single team would reach alone, and each member brings knowledge that expands the group’s overall range of competencies. In 2024, the Chemistry of Materials team secured four European Horizon Programme projects and received invitations from colleagues in the UK and Germany to collaborate on further proposals.
Reference: Kaunas University of Technology. “Indoor solar cells that maximize the use of light energy.” ScienceDaily. ScienceDaily, 25 July 2024. <www.sciencedaily.com
Daniel García is an Editor-in-Chief with strong expertise in structural work and engineering principles. He combines this technical foundation with deep knowledge of energy, spatial design, and emerging technologies, bringing a forward-thinking and analytical approach to editorial leadership.
