CPOS Seminar:"Influences of Metal Electrodes on Stability of High Performed Non-Fullerene Acceptor-based Organic Photovoltaic Devices"

Speaker: SANGCHEOL YOON, Graduate Research Student, Department of Chemistry and Biochemistry, University of California Santa Barbara 

Abstract: Understanding chemical degradation at the interface between different layers in an organic photovoltaic device (OPV) is crucial to improve the long-term stability of OPVs. Herein, the effects of different metal top electrodes on the chemical stability of an active layer in PM6:Y6 bulk-heterojunction (BHJ) OPVs are investigated.  A systematic stability study of thermally annealed devices reveals an inferior stability of OPVs with an aluminum (Al) top electrode compared to silver (Ag) electrode devices. The severe degradation of the Al-electrode OPVs is initiated by thermally induced Al diffusion into the PM6:Y6 active layer. The diffused Al atoms alter Y6 chemical structure, and those undesirable degraded-Y6 molecules give rise to surface recombination at the interface between the PM6:Y6 BHJ layer and an inorganic interlayer (zinc oxide nanoparticles). X-ray photoelectron spectroscopy (XPS) shows that the chemical bonding changes in the PM6 and Y6 are only observed in the presence of Al. The interactions of Al with the Y6 remarkably changes the chemical bonding of sulfur, nitrogen, and fluorine in the Y6 molecules. The chemical degradation of the active layer at the interface drastically deteriorates the device stability of the PM6:Y6 BHJ OPVs.