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Upscaling scenarios are indispensable elements of prospective life cycle assessment (LCA). However, current studies reveal confusing terminology and a wide range of approaches in this area. Therefore, we first defined the term upscaling scenario as the description of a possible future target stage of emerging technology, including the development pathway from a current stage within the course of research and development to this future stage. Second, we developed the novel systematic scheme UpFunMatLCA for generating explorative scenarios based on possible development pathways of the specific group of emerging functional material (FunMat)‐based energy technologies, including status quo developments. UpFunMatLCA represents a three‐step extension of conventional LCAs to upscale the life cycle inventory of emerging FunMats. UpFunMatLCA is based on a clear definition of a current status quo (conceptual, lab, or pilot stage) and a target matured (fab) development stage. A core part of UpFunMatLCA is the so‐called upscaling module, providing specific modeling methods and data for the upscaling of FunMats. Using perovskite solar cells, photovoltaic devices based on several FunMats and attached with great expectations regarding the future efficient provision of solar energy, we demonstrate the application of UpFunMatLCA, focusing on the upstream greenhouse gas (GHG) emissions of the prospective manufacturing. In the discussion, we point out the application area of UpFunMatLCA and the possible extension to depict further environmental impacts beyond GHG to contribute to the sustainability assessment of emerging technologies in the early stages of development.