Every day, light from office lamps, phone screens, and windows pours into rooms and disappears — absorbed by walls, furniture, and floors without generating a single watt. A team of chemists in Lithuania has now synthesized a material designed specifically to capture that overlooked energy, enabling perovskite solar cells to convert indoor light into electricity at efficiencies that exceed those of conventional rooftop panels under their respective testing conditions.
The implications stretch far beyond the lab. Billions of IoT sensors and small electronics currently depend on batteries that need replacing. Cells built with this material could one day draw power from the light already in the room.
The energy hiding in plain sight
Sunlight through a window and the glow of an office lamp share something fundamental: both carry energy that almost entirely goes to waste. Conventional solar panels are engineered for direct, high-intensity sunlight — the kind found on rooftops, not in living rooms. Standard photovoltaics simply can’t operate efficiently under the dim, warm-toned light typical of indoor environments.
That gap matters more than it once did. The IoT sector has expanded rapidly, filling homes, hospitals, and factories with smart sensors, wearables, and connected devices. Nearly all of them run on batteries. Indoor photovoltaics — cells designed for low-intensity artificial or diffused natural light — could shift that equation by turning ambient light into a usable power source.
A molecule built for the job
The key advance came from Dr. Asta Dabulienė, a senior researcher at KTU’s Chemistry of Materials group, who synthesized a series of new thiazolo[5,4-d]thiazole derivatives—organic semiconductors engineered to serve as hole-transporting layers inside perovskite solar cells.
These layers perform a specific function: they selectively move positive charge carriers, called holes, while blocking electrons. That selectivity reduces recombination losses — the process by which charges cancel each other out before contributing useful work — and directly improves cell efficiency.
“An ideal hole-transporting semiconductor for these applications would possess high hole mobility and good energy-level alignment with those of adjacent layers,” Dr. Dabulienė explains. One derivative stood out above the rest. The compound incorporating a triphenylamine donor fragment combined exactly the structural properties needed to perform well under indoor light conditions.
37% efficiency under LED light
Researchers at Ming Chi University of Technology in Taiwan took the KTU-developed semiconductor and used it to build perovskite solar cells optimized 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%. Typical commercial silicon solar panels achieve around 20–22% efficiency under standard outdoor test conditions. The indoor figure doesn’t just close that gap; it surpasses it.
That comparison warrants some nuance, though. Indoor and outdoor cells operate under very different light intensities, so the numbers aren’t directly interchangeable. Even so, the result demonstrates that thiazol[5,4-d]thiazole derivatives carry genuine potential for pushing indoor photovoltaic performance to commercially meaningful levels.
A three-continent collaboration
No single institution produced this result. The work was divided across three research groups on three continents, each contributing a distinct piece.
KTU in Lithuania synthesized and characterized the organic semiconductors. Scientists at King Abdullah University of Science and Technology in Saudi Arabia handled the theoretical modeling of the new compounds, while the team at Ming Chi University of Technology in Taiwan constructed and tested the finished perovskite cells.
Professor Gražulevičius notes that international cooperation expands what any single group can accomplish. His Chemistry of Materials group already reflects that philosophy—its members come from Lithuania, Ukraine, India, Pakistan, Armenia, Egypt, and Nigeria. In 2024 alone, the group secured four European Horizon Programme projects. Cross-cultural collaboration brings real challenges: communication gaps, different working cultures, and organizational complexity. But those friction points, he argues, are worth navigating. Different backgrounds generate different ideas, and that variety drives innovation in ways a homogeneous team rarely can.
What this means for everyday devices
The practical applications are tangible. Perovskite IPV cells could be embedded directly into mobile phones, smart home sensors, pocket flashlights, and other small electronics, allowing them to harvest ambient light already present in a room rather than drawing down a battery.
Through IoT frameworks, that harvested electricity could regulate device operation in real time and optimize energy consumption across entire networks of connected devices. The research team identifies high performance, low cost, and versatility as the pillars any commercially viable indoor photovoltaic solution must satisfy.
Wider adoption would carry a broader benefit. Reducing dependence on disposable batteries — billions of which are discarded every year — would represent a meaningful, if incremental, contribution to renewable energy goals. The next step is scaling the material and moving it closer to manufacturable devices. That work is now underway, and the 37% benchmark gives researchers a clear target to build from.
Kelly is an experienced writer with 15 years of experience exploring the big stories that shape our world, from tech breakthroughs and space exploration to climate, energy, and the fascinating quirks of science. She has a talent for turning complex ideas into sharp, memorable insights that stay with readers long after they’ve finished reading.
