Klaus Lips
Silicon Thin Film
Helmholtz-Zentrum Berlin für Materialien und Energie (HZB)
Hahn-Meitner Platz 1, 14109 Berlin, Germany
Email: lips@helmholtz-berlin.de
Biography
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Klaus Lips is Professor for Physics at the Freie Universität Berlin (FUB); Germany and holds two Adjunct Professorships at the University of Utah, Salt Lake City, USA and Monash University, Melbourne, Australia. He is heading the department Spins in Energy Materials and Quantum Information Science (ASPIN) at the Helmholtz-Zentrum Berlin für Materialien und Energie (HZB) in Berlin and is speaker and coordinator of a large German research network devoted to the development and application of the EPRoC technology (Electron Paramagnetic Resonance On a Chip). Klaus studied physics at the University of Leiden, (Netherlands) and University of Marburg (Germany), where he received his PhD in 1994. He worked at the National Renewable Energy Laboratory (NREL), Colorado, USA and joined HZB, formerly Hahn-Meitner Institut Berlin in 1996. His research interests are transport and defect states in semiconductor materials, novel solar cell technologies, and the application and development of new EPR- and NMR-based techniques for material research and detection of ultra-small spin ensembles (quantum sensors). Klaus has pioneered electrical detection of spin coherence in silicon and is author of over 200 journal papers and holds 14 patents (several for EPRoC) and has given over 160 invited lectures at many national and international conferences and research schools. Klaus has received many scientific prizes among which HZB’s Technology Transfer Prize, which was awarded in 2019 jointly also to Jens Ander (Univ. Stuttgart, Germany) for the development of EPRoC. Klaus is a passionate triathlete and marathon runner and has participated in numerous competitions. |
Abstract for Presentation
Unravelling the room temperature non-radiative recombination mechanism
at dangling bonds in hydrogenated amorphous silicon
Although the macroscopic optoelectronic properties of electronic devices can be well simulated even if they contain amorphous silicon (a-Si:H), e.g. HZB’s 29.8% efficient c-Si heterojunction/perovskite tandem solar cell [1], we still lack a good understanding of the nanoscopic process of charge trapping and recombination through dangling bond (db) defects in a-Si:H. In device simulation, it is always assumed that the charge carriers recombine through a direct capture process at dbs following Shockley-Read-Hall (SRH) statistics without taking the electron and defect spin of the SRH process into account. As will be shown in this presentation, the electron and db spin play an important role in recombination and serve as observers to unravel the nanoscopic mechanism of SRH recombination.
Using density-functional theory (DFT) and multifrequency (100 MHz–263 GHz) pulsed electrically detected magnetic resonance (pEDMR) spectroscopy, we show that dbs in the a-Si:H matrix form under forward bias injection conditions in an a-Si:H pin solar cell at room temperature metastable spin pairs between bandtail electrons (cbt) and dbs in a well-defined quasi two-dimensional (2D) configuration. Although highly localized, these pairs exhibit nearly vanishing dipolar and exchange coupling. The formation of this 2D magic configuration involves a > 0.3 eV energy relaxation of the trapped electron, stabilizing the spin pair and causing a microsecond long RT spin-coherence time. It will be demonstrated that relaxation of the amorphous silicon lattice is essential to form this µs-long coherent cbt-db complex which acts as precursor state of db recombination. This existence of a precursor state of db recombination solves a 40 yearlong discussion about the mechanism of non-radiative electron-hole recombination through db states in a-Si:H [2] and this cbt-db complex state is capable, for the first time, to explain all experimental observations in room temperature pEDMR.
References
[1] https://www.helmholtz-berlin.de/pubbin/news_seite?nid=23248&sprache=en&seitenid=74699
[2] H. Dersch, L. Schweitzer, J. Stuke, Phys. Rev. B 28 (1983) 4678.
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