Materials Challenges in Photovoltaic Energy Generation in Space

Virtually all spacecraft employ photovoltaic energy conversion for continuous power generation. Compared to their counterpart on Earth, photovoltaic modules in the space environment face a unique set of performance requirements. Among the most demanding ones are the need to have the highest possible specific power output with regard to mass and surface area while showing as little degradation as possible under intense particle and ultraviolet radiation during lifetimes of up to 15 years. In addition, the thermomechanical stresses induced by temperature fluctuations up to 200°C are not to result in additional electrical degradation. This article briefly outlines the state-of-the-art design solution to meet these requirements before it focuses on current materials issues in two core areas: On the solar cell itself, which requires new materials systems and cell concepts to surpass the efficiency of the lattice-matched triple junction solar cell technology, and on materials issues concerning the encapsulation of solar cells for space use. Closely linked to these materials challenges are testing-related issues that arise in verifying the expected material behaviour during extended periods in the space environment. These are discussed in conjunction with the materials challenges.