Fraunhofer Develops Solar Cells With Over 40% Efficiency Indoors, Study Finds

Researchers at the Fraunhofer Institute for Solar Energy Systems ISE have made significant strides in the development of solar cells based on III-V semiconductors, with indoor efficiencies surpassing 40 percent. These findings by the Fraunhofer Institute were detailed in the journal Applied Physics Letters.

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By refining both the design and absorber material quality of their solar cells, the research team at the Fraunhofer Institute claims to have achieved high efficiencies even under subdued light conditions, as low as 100 lux. This result makes this technology particularly attractive for autonomous Internet of Things (IoT) applications that operate indoors without an external wired power supply. 

Since Indoor photovoltaics draw on artificial light indoors to generate electricity, this technology presents an attractive solution for devices that can’t be routinely recharged, particularly the many untethered components found in IoT systems.

“Various photovoltaic technologies can be used for this purpose,” explains Henning Helmers, Head of Department at Fraunhofer ISE. “Solar cells based on III-V semiconductors reach the highest efficiencies, especially applied to artificial (LED) light.”

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Key Findings

In their study, the researchers optimized gallium indium phosphide (GaInP) solar cells, as their band gap is almost ideal for converting visible light into electricity. "We investigated how well the solar cells with different architectures work under low light conditions", summarizes Malte Klitzke, lead author of the study and scientist at Fraunhofer ISE. "It was shown 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 us to achieve very high efficiencies with them in our experiments when converting weak indoor light into usable power."

The research result combines findings from several research projects: “50Percent,” funded by the Federal Ministry of Economics and Climate Protection (BMWK); "H2Demo," funded by the Federal Ministry of Education and Research (BMBF); and “SMART,” supported by AZUR SPACE Solar Power and the German Space Agency (DLR).