A gravity independent integrated passive cooler for solar cell efficiency improvement

Efficient temperature control is an important topic in solar cell development due to the high amount of energy converted into heat. In this context the implementation of heat spreaders as passive devices is of great interest. This contribution concerns an original cooling solution that provides both a high heat conduction coefficient and high level of miniaturization. Integrated in the substrate of the electronic device, the vapor chamber heat spreader is a passive device that provides robustness (absence of mobile parts), with a high conduction coefficient related to the capillary pumping of the liquid. As the dissipated heat flux strongly depends on several parameters, the integration of internal sensors is very useful in order to have in-situ measurements for the optimization of the device. A first prototype of the heat spreader with integrated temperature and pressure micro-sensors has been realized and tested. The heat extraction capability differences have been evidenced using different filling ratio and different cooling liquids. For a hot spot temperature of 70°C, a temperature reduction of about 25% being observed for a 10% ethanol filling of the cavity. Considering the open circuit voltage (V_OC) dependence on the temperature, the temperature drop corresponds to a decrease of V_OC by 25% and thus an important increase in the solar cell efficiency, especially in concentrator solar cells.