At the Helmholtz Zentrum Berlin für Materialien und Energie (HZB), we conduct research on complex systems of materials that contributes to dealing with challenges such as the energy transition. The HZB research portfolio includes solar cells, solar fuels, thermoelectrics, and materials for new, energy-efficient information technologies (spintronics) or electrochemical energy storage. Research on these energy materials is closely connected with the operation and advanced development of the BESSY II photon source. And our research approach always concentrates on thin-film technologies.