Enhancing passive radiative cooling properties of flexible CIGS solar cells for space applications using single layer silicon oxycarbonitride films

Satellites in lower earth orbits have been primarily powered by photovoltaic modules. With growing power demand for new satellite concepts, solar cells are required to be flexible and ultra-lightweight to decrease launch costs. CIGS thin film solar technology is a promising candidate, since it can be manufactured on flexible substrates and possesses high radiation hardness. Poor radiative properties of CIGS on the other hand, lead to high temperatures and therefore power loss. High emissivity coatings on CIGS have already been reported but the influence on thermal and electrical aspects have not been addressed. Here we present the optical properties of silicon-oxycarbonitride coatings and their effect on electrical parameters on CIGS cells to be used for the DLR's GoSolAr power sail mission. We show that the single layer coating can significantly increase emissivity from 0.3 to 0.72, with minimal spectral losses and negligible impact on the functioning of the underlying CIGS cell. We simulated the thermal impact of the coating on solar cells in orbit and can predict that the maximum temperature of the cells is reduced by 30 degrees C, resulting in a significant power gain. Additionally, the coating has an emissivity of 0.87 in the atmospheric window of 8-13 mu m making it a very good passive radiative cooler for terrestrial solar cells. The low-cost coating can replace glass and the process can be scaled up for large CIGS modules. The coating can also significantly increase the power to mass ratio of solar modules, reducing costs for space applications.