We develop special photovoltaic cells – so-called “laser power converters” – that convert monochromatic light into electricity with the highest efficiency. These cells are used to power sensors and actuators, when a conventional power transmission via copper wires is impossible or limited, e.g. due to requirements for galvanic isolation, lightening protection, electromagnetic interference, wireless power transmission, spark prevention, corrosion resistance, high magnetic fields or rotating systems. The applications for these converters are numerous. Examples are: the structural health monitoring of wind turbines, the monitoring of high voltage power lines, fuel gauges in aircraft, optical powering of automotive sensors, biosensors in smart implants, or monitoring of passive optical networks (PON).
To transmit power in the form of light, a light source produces monochromatic light. The light is transmitted through the air or via an optical fiber to the receiver. The photovoltaic cell converts the monochromatic light into electricity. If an optical fiber is used, both the power and data transmission can be realized with a single fiber. Thus, systems can be electrically powered and monitored at the same time.
By using specially adapted photovoltaic cells, monochromatic light can be converted into electricity more efficiently as compared to the conversion of the spectrally distributed solar radiation with conventional solar cells . The key lies in the matching of the semiconductor’s bandgap to the wavelength of light, thus minimizing the thermalization and transmission losses. With cells based on GaAs, we have demonstrated an efficiency of 54.9 %, measured at a laser wavelength of 810 nm (36.5 W/cm²).
III-V compound semiconductors cover a wide range of laser wavelengths. Examples for materials are: Ga0.51In0.49P (660 nm), GaAs (870 nm), Ga0.83In0.17As (1050 nm), Ga0.16In0.84As0.31P0.69 (1100 nm), Ga0.47In0.53As (1680 nm) or GaSb (1700 nm). The cutoff wavelength is given in parentheses.
Besides material development, we also design and optimize individual cell concepts for different operating conditions as well as integrated series-connected cell architectures for increased output voltages (vertically stacked multi-junction cells and laterally segmented cells i.e. monolithic interconnected modules (MIM)). The typical output voltage of segmented cells based on GaAs (with e.g. 2, 4, 6 or 12 segments) is the number of segments multiplied by one volt.
We have a laser-based measurement setup for performing characterizations under monochromatic light at our disposal. Here we can carry out calibrated and reproducible measurement sequences under defined conditions.
Selected publications on this topic (Fraunhofer-Publica database)