The Fraunhofer Institute for Solar Energy Systems ISE has developed solar cells based on III-V semiconductors that achieve an efficiency of over 40 percent indoors. According to Fraunhofer ISE, by optimizing the design and material quality of the absorber, the research team was able to achieve exceptionally high efficiencies even in very low light conditions of only 100 lux.
Indoor photovoltaics use indoor light to generate electricity. This technology is particularly useful for devices that cannot be constantly recharged, such as many components in IoT (Internet of Things) systems. »Various photovoltaic technologies can be used for this purpose,« explains Henning Helmers, department head at Fraunhofer ISE. »III-V-based solar cells currently have the highest material costs, but they are also the most efficient, especially under artificial (LED) light.«
In their study, the researchers optimized gallium indium phosphide (GaInP) solar cells because their band gap is almost ideal for converting visible light into electricity. When excited with a 405 nm laser, the GaInP indoor solar cell begins to glow bright red, as can be seen in the photo.
»We investigated how well solar cells with different structures perform under low light conditions,« says Malte Klitzke, lead author of the study and scientist at Fraunhofer ISE, summarizing the results. »We found that a certain type of solar cell, the n-doped GaInP cell, performs significantly better than the p-doped variant. N-doped GaInP cells retain charge carriers longer and have increased performance, even in low light. That is why we were able to achieve very high efficiencies in converting indoor light into electricity in our experiments.«
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