Researchers at Germany’s Fraunhofer Institute for Solar Energy Systems (Fraunhofer ISE) have developed solar cells based on III-V semiconductors that can achieve over 40% efficiency indoors.

Fraunhofer ISE stated that the researchers optimized the design and improved the quality of the solar cell absorber material to achieve high efficiencies, even in low-light conditions of 100 lux.

This result makes this technology particularly attractive for autonomous Internet of Things applications that operate indoors without an external wired power supply. The findings were published in the journal Applied Physics Letters.

The type III-V compound semiconductors possess versatile properties, including a direct bandgap, higher carrier mobility, and a smaller effective electron mass. Such attributes make them attractive for applications in solid-state lighting, wireless communication, artificial intelligence, high-speed trains, clean energy generation, and radar systems.

Henning Helmers, Head of Department at Fraunhofer ISE, said, “Solar cells based on III-V semiconductors reach the highest efficiencies; this especially applies to artificial light.”

The researchers optimized gallium-indium phosphide (GaInP) solar cells, as their band gap is almost ideal for converting visible light into electricity.

The researchers found that the n-doped GaInP cell performs significantly better than the p-doped cell. Charge carriers in n-doped GaInP cells have a longer lifetime, and thus they can produce more electricity even under weak light. This enabled them to achieve very high efficiencies in experiments when converting weak indoor light into usable power.

In May this year, scientists at Fraunhofer ISE claimed to have produced silicon heterojunction solar cells with a total silver consumption of 1.4 mg per watt of peak power.

Researchers at the Massachusetts Institute of Technology demonstrated a new interface architecture that pushes the traditional silicon solar cell’s efficiency beyond the long-standing single-junction theoretical limit of 29.4%.