Investigating the Potential of Copper(II) Acetylacetonate as an Interfacial Buffer Layer in Organic Photovoltaics
Matthew Dingley a, Ross Hatton a
a Department of Chemistry, University of Warwick, Coventry, CV4 7AL, United Kiongdom
International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV22)
València, Spain, 2022 May 19th - 25th
Organizers: Pablo Docampo, Eva Unger and Elizabeth Gibson
Poster, Matthew Dingley, 231
Publication date: 20th April 2022

Copper (Cu) is a potential alternative to silver (Ag) as the reflective electrode in inverted organic solar cells because it is approximately 1% of the cost, with comparable electrical conductivity and higher work function. However, due to its higher susceptibility to oxidation in air than Ag it is not widely used for this purpose. Our group, and others, have shown that the rate of oxidation of Cu films actually depends very strongly on the structure and morphology of the film and can be extremely slow after oxidation of the first few nanometres, even for polycrystalline Cu films. This implies that for the metal thickness used as an opaque electrode (≥100 nm) oxidation of the top exposed surface of the Cu electrode is unlikely to be the fastest degradation mechanism in an organic solar cell. Indeed, a Cu top electrode could actually serve the dual role of low cost electrode and built-in desiccant for low levels of oxygen and water ingress in encapsulated PV devices. Furthermore, if the buried interface is oxidised to CuO and/or Cu2O, due to oxygen and water ingress into the photoactive layer, the barrier to hole-extraction could be minimal, since both are p-type semiconductors with almost identical valence band edge energies that are well-aligned with the ionisation potential of donor type organic semiconductors used in organic solar cells. This poster presents the result of an investigation into the potential of copper(II) acetylacetonate (Cu(AcAc)­2) as a buffer layer between the photoactive organic layer and the Cu top electrode. Cu(AcAc)2 can be solution processed from alcoholic solutions directly onto films of organic semiconductor and decomposes at low temperature to form metallic Cu, so has the potential to seed the formation of a compact Cu electrode on top of the photoactive organic semiconductor layer.

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