Neutrons for Science and Industry

Point defects and their impact in next generation solar cells revealed by in-situ positron annihilation spectroscopy

by Dr Stephan Eijt (Delft University of Technology)

PH HS 3 (Physics Department)


Physics Department

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Positron Annihilation Spectroscopy (PAS) is a very sensitive method to reveal the presence of vacancy-related point defects in thin film solar cells. Its depth-range and resolution matches various types of existing and emerging thin film solar cells. We apply Positron annihilation spectroscopy (PAS) to monitor environmental degradation of ZnO/CIGS and of perovskite solar cells. Furthermore, we examine the presence of point defects and near-surface oxidation of thermally annealed RF-sputtered BaSi2 thin films. We show that the positron is a very sensitive probe for the surfaces of semiconductor quantum dots in thin film QD photovoltaic systems. Ab-initio modelling in combination with Positron Annihilation Lifetime Spectroscopy (PALS) provided first-time proof of the presence of the positron surface state underlying the very high sensitivity of positrons to probe surfaces of CdSe quantum dots. 

During the last decades PNIPAM-based microgels were widely studied and serve nowadays as model systems for the investigation of the basic properties of microgels and the principles of supported transport of active substances, e.g. drug delivery. 

This work focuses on a detailed analysis of PNIPAM microgels in solution and at interfaces with scattering experiments. Neutron and X-ray scattering provide a unique insight into the structure and dynamics of microgels, especially at the interface with grazing incidence small angle neutron scattering and neutron spin-echo spectroscopy (GISANS and GINSES). New aspects of the inner structure and dynamics are gained with improved experimental conditions and data analysis. Simulation of the scattering signal within the Distorted Wave Born Approximation is presented in order to improve the analysis of the GINSES data and to simplify the initial planning and performance of the grazing incidence experiments.


[1] T. Kyrey, M. Ganeva, K. Gawlitza, et al., Physica B: Condensed Matter (2018) 551, 172–178, doi:10.1016/j.physb.2018.03.049.

[2] T. Kyrey, J. Witte, V. Pipich, et al., Polymer (2019) 169, 29–35, doi: 10.1016/j.polymer.2019.02.037.

[3] J. Witte, T. Kyrey, J. Lutzki, et al.,  Soft Matter (2019) 15, 1053–1064, doi: 10.1039/c8sm02141d.

Organized by

Dr.Alexandros Koutsioumpas
Dr. Christian Franz