Investigation of the Phase Separation in Non-Fullerene Organic Solar Cells by AFM and GIWAXS

Further progress in the synthesis and fabrication of new solar cell devices strongly depends on the ability to measure their properties rapidly with highest precision. Such solar cell assemblies are often synthesized in the form of thin films (film thickness typically smaller than 200 nanome-ters). The measurement of such films is challenging and often complimentary methods are needed to fully understand the function of such films. With atomic force microscopy (AFM using Tosca 400) and grazing-incidence X-ray scattering methods (GISAXS/GIWAXS with the SAXSpoint 2.0 system) Anton Paar can offer state-of-the-art solutions for the characterization of such advanced solar devices.

Introduction

The device performance of bulk-heterojunction solar cells strongly depends on the donor and acceptor properties, the phase separation in the absorber layer and the formation of a bicontinous network. In the case of polymer:fullerene solar cells this phase sepa-ration is well known. However, little is known about the phase separation in polymer:non-fullerene accep-tor solar cells. Due to the chemical similarity of the conjugated polymer donor and the organic non-fullerene acceptor structural analysis by methods such as conventional transmission electron microscopy is difficult. Complementary surface-sensitive methods, such as atomic-force microscopy (AFM) and grazing-incidence small- and wide-angle scattering (GISAXS/GIWAXS), help to get a deeper understanding of the phase morphology in such systems.

While AFM can measure and analyze features such as the surface morphology and roughness of thin films, GIWAXS can also probe sub-surface structures and thus give information also on e.g., phase separa-tion and ordering throughout the thin film.[1] Due to the large probed sample volume in GISAXS/GIWAXS also data with excellent statistics is obtained that is very much complementary to microscopy measurements such as AFM.

References

1. Schnablegger, H.; Singh, Y., The SAXS Guide - Getting acquainted with the principles. 4th ed.; Anton Paar GmbH: Graz, Austria, 2017.

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