The ACT-FAST project aims to develop a new type of thin-film tandem photovoltaic (PV) technology to drive the clean energy transition. The project, funded by the European Commission, seeks to create scalable and impactful PV solutions that can be rapidly transferred and widely adopted by society. The project focuses on producing high-power density solar technology with long-term stability and a wider range of applications than traditional silicon-based modules. It aims to develop high-efficiency thin-film tandem solar cells using low-cost techniques and low environmental impact materials. The long-term vision of the project is to deliver thin-film tandem solar cells and modules with power conversion efficiencies of at least 25% at low manufacturing costs. The project involves collaboration between four European research institutions and aims to contribute to building a sustainable and competitive mass production process for thin-film tandem PV.