Galvanic metallization of solar cells is ideal for efficient current flow at high electrical outputs. The process thus opens up new possibilities for classic silicon solar cells and, in particular, for solar cells in special applications such as laser power cells, which are used for wireless power transmission.
Researchers at Fraunhofer ISE in Freiburg have succeeded in depositing galvanically reinforced conductor tracks on such laser power cells. This was done directly from a chemical solution into a paint mask. Contact fingers with a height of 15 µm were produced, which is about five times the height of conventional fingers. This allows higher currents to be dissipated with virtually no loss.
Solar cells typically generate a high current at a comparatively low voltage. The loss-free dissipation of the current generated by the incident light is therefore particularly important for high efficiency. This applies increasingly to solar cells that are very strongly illuminated, because the current increases proportionally with the intensity of the irradiation, but the resistance losses increase quadratically with the current. This applies on the one hand to III-V solar cells under concentrated light incidence and on the other hand to so-called laser power cells, which are used for wireless energy transmission. In such power-by-light applications, high-intensity laser light is used to transmit energy and converted back into electrical energy at the receiver using a photovoltaic cell.
"Galvanic metallization is a very exciting technological option for our laser power cells"
"Galvanic metallization is a very exciting technological option for our laser power cells," says Henning Helmers, Deputy Head of Department III-V Photovoltaics and Concentrator Technology at Fraunhofer ISE. Even when irradiated with a laser power of 62.6 watts, the cells exhibit only moderate resistance losses due to the current transport in the metallization. With a cell efficiency under laser light of 57-61 %, depending on the irradiation, the research team was able to achieve electrical outputs of over 35 watts from an area of just 1 cm2. "In the future, significantly higher outputs are conceivable with this technology. With an adapted design with a stacked cell structure, power transfers of hundreds of watts can also be achieved. This means that further applications with higher power requirements for optical power transmission can be developed in the future," says Helmers.
"Electroplating the laser power cells works without difficulty and very quickly once a suitable design has been developed," says project manager Jonas Bartsch. The process enables compact layers of highly conductive metals, such as copper or silver, with very high growth rates in the range of several micrometers per minute. Layer thicknesses of 50 µm and more can easily be produced. At the same time, the process runs at a low temperature, which reduces process costs. As this is an additive manufacturing technique, unlike other metallization processes, only as much metal is required as is actually deposited. In this way, the necessary use of resources is optimized.
