HZB-Electron Paramagnetic Resonance Facility for defects and impurities characterisation

MAIN FEATURES:

The Electron Paramagnetic Resonance Facility at HZB ( EPR@HZB) allows for the characterization of paramagnetic states such as many known defects in materials implemented in solar cells. One of the most prominent defects characterized by this technique are

• broken silicon bonds, (dangling bonds) in thin-film silicon, c-Si and μc-Si.
• Analysis of defects and impurities in semiconductor materials can be quantified at levels as low as 10¹³/cm³ depending on the specific nature of the paramagnetic specimen involved.

The EPR signature allows a microscopic identification of the involved specimen through their characteristic EPR fingerprint

EPR@HZB has several spectrometers covering the microwave frequencies from 9 GHz up to 263 GHz with multi-frequency options such as ENDOR (Electron Nuclear Double Resonance).

Typical samples sizes suitable for EPR measurements are 4 x 10 x 4 mm3

LIMITATIONS OR CONSTRAINTS :

EPR characterization is generally limited to paramagnetic states or defects. It is routinely used:

• to characterize powder samples relevant for pv applications like non-crystalline silicon of varying morphology
• Organic PV blends.
• Characterization of fully processed solar cell structures by electrically or optically detected EPR is feasible, but requires special sample structures

TYPICAL SERVICES OR RESULTS

EPR@HZB is regularly used for :

• the characterization of silicon and organic solar cells and
• their components
• surface analysis of silicon
• physical chemistry (catalysts for solar fuel production) and biology
• (Photosynthesis).

Typical examples of PV applications are the :

• The determination of the defect density in thin-film Si absorber layers
• measurement of impurity concentration (e.g. phosphorous, metals) in crystalline silicon.

Apart from the Institute of Silicon Photovoltaics, which runs the facility, numerous other groups in the field of thin-film PV are involved in using this equipment, mainly from research institutions in Germany through the network project EPR-Solar but also from the PV industry and from partners in Spain, Switzerland, France, Netherlands, the Czech Republic, and the US

Participation to Research Projects:

EPR applications to PV materials are described in more details on HZB web page 8see enclosed links)