Solar cells achieve high efficiency indoors

Energy

Technological Innovation Website Editorial Team - July 10, 2025

The star of the new solar cell is its material, perovskite. [Image: Chia-Tse Hsu et al. - 10.1063/5.0260714]

Perovskite solar cells

Solar energy is about to lose its exact and rigorous meaning, thanks to an emerging solar cell technology.

Perovskite solar cells have emerged as a lower-cost, higher-efficiency alternative to traditional silicon solar cells due to their structure and physical flexibility. Their high power conversion efficiency—the amount of energy generated from the amount of energy reaching the cell—makes these cells suitable for generating electricity using weaker light sources.

Indeed, Chia-Tse Hsu and colleagues at National Chiao Tung University in Taiwan have created perovskite solar cells that effectively convert indoor lighting into electrical energy—solar cells that do without direct sunlight.

"The most common solar cells on the market are silicon-based solar panels," commented Professor Fang-Chung Chen. "However, perovskite solar cells can be thin, light, flexible, and even semi-transparent, while silicon panels are rigid and heavy, limiting their use to flat, durable surfaces."

And it's not just a matter of where to place the panels: Perovskite cells are more efficient than silicon cells indoors.

Under standard sunlight (nearly 12,000 lux), the perovskite cells achieved a power conversion efficiency of 12.7%, which, compared to the best silicon solar cells at 26%, isn't much. However, the perovskite solar cells achieved an impressive 38.7% efficiency under 2,000 lux, a brightness that's a fraction of the sunlight on a sunny day and a brightness level similar to that found in offices.

Surface textures of perovskite layers prepared under different conditions to find the best way to correct material defects. [Image: Chia-Tse Hsu et al. - 10.1063/5.0260714]

Forbidden band

To create a solar cell capable of converting internal light into electricity, researchers needed to adjust the perovskite's bandgap .

The energy gap—or band gap—describes the minimum energy required for electrons to jump to higher energy levels, and different band gaps can absorb different wavelengths of light. By adjusting the proportions of molecules in the solutions used to form the perovskite layers that make up solar cells, researchers were able to achieve an ideal band gap for absorbing internal light—a tuning not possible in silicon solar cells.

"The internal efficiency of perovskite solar cells is higher, which means that photovoltaic products can be better suited for versatile use cases, including outdoor, indoor, and other low-light and cloudy environments," Chen said. "Adjusting the bandgap, unfortunately, has a negative effect: it causes defects in the perovskite layers. To compensate for the loss in efficiency, we proposed a method to correct the defects."

Somewhat surprisingly, the team's method made the solar cell less susceptible to corrosion and even increased its overall efficiency.

"Initially, we only hoped that our approach could improve device efficiency," Chen said. "Since the low reliability of perovskite solar cells poses a major challenge to their adoption, we hope our method can pave the way for the commercialization of perovskite solar panels."

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