Moisture Ingress and Distribution in Bifacial Silicon Photovoltaics

Water drives various modes of degradation in photovoltaic (PV) modules, ranging from encapsulant yellowing and delamination to contact corrosion. In silicon PV modules, the primary route of moisture ingress is diffusion through the polymeric module components (encapsulant and, when present, backsheet). Understanding the behavior of moisture in modern encapsulants and architectures is crucial for projection and, ultimately, mitigation of moisture-induced degradation. To this effect, we quantify the solubility and diffusivity of water in four state-of-the-art encapsulants for bifacial silicon PV modules: ethylene vinyl acetate (EVA) and polyolefin (POE), each with and without UV-blocking additives. Using water reflectometry detection (WaRD), we track the “breathing” rate of water indiffusion and outdiffusion in miniature bifacial modules of both glass-glass and glass-backsheet configurations. Crucially, we separate module moisture content from in front and back of the silicon cell. Overall, we present a quantitative picture of how moisture moves within modern bifacial silicon PV modules.