Strukturforschung mit XFELs und Synchrotronstrahlung








The lecture series "Materials Research with Free-Electron X-Ray Lasers" will take place from 20.09. - 25.09.2020. Due to the ongoing unclear situation with the COVID-19 pandemic we took the decision to replace the lecture series in Hamburg with an online lecture event during the same time period, thus from 21. - 25. September 2020. We are currently preparing the new format and hope to find a lively and interactive concept. Moreover, an interactive virtual tour through the facilities European XFEL and FLASH will be organized. If you are interested in joining this exceptional lecture series we would like to encourage you to register via OPAL.

  • Registration until 14.08.2020 via OPAL

Recent highlights

Observing electrons harvesting light on the nanoscaleShort X-ray pulses measure how efficient visible light is transformed into separate electric charges with nanometer precision and single-electron sensitivity

Despite substantial efforts to develop plasmon-enabled light-harvesting technologies, overall device efficiencies remain rather low, with most groups reporting external quantum efficiencies well below 1%. Progress in future developments depends on a better understanding of the operating principles and current limitations on fundamental length- and time-scales. Here, we employ picosecond time-resolved X-ray Photoelectron Spectroscopy to investigate photoinduced electron transfer in a plasmonic model system composed of 20 nm sized gold nanoparticles (AuNPs) attached to a nanoporous TiO2 film The measurements provide direct and quantitative access to transient local charge distributions from the perspectives of the electron donor (AuNP) and the electron acceptor (TiO2). On average, approximately two electrons are injected per AuNP, corresponding to an electron injection yield per absorbed photon of 0.1%. Back electron transfer from the perspective of the electron donor is dominated by a fast recombination channel proceeding on a timescale of 60±10 ps and a minor contribution that is completed after ≈1 ns. The findings provide a detailed picture of photoinduced charge carrier generation in this NP-semiconductor junction, with important implications for achievable overall photon-to-charge conversion efficiencies and improved device designs. Moreover, the reported results represent the first reference-free, quantitative, microscopic, and real-time study into the efficiency and temporal evolution of charge transfer dynamics in a standard nanoplasmonic heterostructure.

For further information contact:

Dr. Friedrich Roth

Further reading:

M. Borgwardt, J. Mahl, F. Roth, L. Wenthaus, F. Brauße, M. Blum, K. Schwarzburg, G. Liu, F. M. Toma, O. Gessner
Photoinduced Charge Carrier Dynamics and Electron Injection Efficiencies in Au Nanoparticle-Sensitized TiO2 Determined With Picosecond Time-Resolved X-Ray Photoelectron Spectroscopy
J. Phys. Chem. Lett. 11 (2020) 5476

Optical pump and X-ray probe experiment

Slow charge generation plays big role in model material for solar cells

Using mixtures of organic molecules to turn light into electric charges has long been a promising concept for renewable energy supplies but has not found widespread application due to limited efficiencies, the underlying reasons of which are not fully understood. An important model system to study these fundamental light-to-charge conversion processes consists of a combination of copper-phthalocyanine (CuPc) and C60 molecules, whereby light is absorbed in the CuPc molecules to generate so-called excitons that travel towards the interface with the C60 molecules, where they can separate into electric charges. Excitons come in different characters, designated singlet and triplet, which may have very different charge generation capabilities but they are notoriously hard to track. Our recent study provides, for the first time, relative charge generation efficiencies from singlet and triplet excitons in a CuPc-C60 heterojunction. Contrary to common belief, the slowly traveling triplet excitons contribute to a significantly larger extent to the total charge than the much faster but short-lived singlet excitons. The findings constitute an important advance in the atomic-scale understanding of the electronic dynamics underlying emerging molecular electronics concepts.

For further information contact:

Dr. Friedrich Roth

Further reading:

F. Roth, S. Neppl, A. Shavorskiy, T. Arion, J. Mahl, H. O. Seo, H. Bluhm, Z. Hussain, O. Gessner, W. Eberhardt
Efficient charge generation from triplet excitons in metal-organic heterojunctions
Physical Review B 99 (2019) 020303(R)


Materials Research with Free-Electron X-Ray Lasers

2 SWS lecture series in Hamburg at DESY & EuXFEL
20. bis 25. September 2020

Ankündigung 2019