Klaus Ellmer received the diploma degree in physics from the Humboldt university in Berlin (GDR) in 1974, and the Ph.D. degree in 1980. For 11 years he worked as a project manager in the semiconductor industry for thin film deposition for integrated CCD image sensors (charge-coupled devices) before in 1991 joining the Hahn-Meitner-Institut in Berlin, now named „Helmholtz-Zentrum für Materialien und Energie“ (HZB).  At the HZB he is  a member of the staff of the division of solar energy research, dept. „Solar Fuels“, which focuses on research and development of materials and devices for water splitting. He is responsible for the reactive magnetron sputtering group.
His research fields are the deposition of all layers for thin film solar cells (TFSC), especially of wide bandgap semiconductors (ZnO, SnO2, ITO, TiO2) and sulfidic and selenidic compound semiconductors (FeS2, WS2, WSe2, MoS2, RuS2, CdS, CuInGaS2, CuInGaSe2) by (reactive) magnetron sputtering and the in situ characterization of magnetron plasmas and of thin films by energy-dispersive mass spectrometry and energy-dispersive, time-resolved X-ray diffraction (EDXRD) at synchrotron radiation sources. Recently, he has written a chapter on magnetron sputtering for thin film solar cells and edited a book on zinc oxide electrodes for TFSCs. K. Ellmer is a member of the German Physical Society (DPG) and of the Materials Research Society (MRS).