Old Clusters with New Applications: Engineering Physical Properties in Keggin and Dawson Polyoxometalates for Application in Organic Optoelectronics

Maria Vasilopoulou^a, Antonios Douvas^a, Panagiotis Argitis^a, Stella Kennou^b, Leonidas Palilis^c

^aNational Center for Scientific Research Demokritos, Terma Patriarchou Grigoriou, Athens, 15354, Greece

^bDepartment of Chemical Engineering, University of Patras, 26500 Patras, Greece

^cUniversity of Patras, Department of Physics, 26500 Patras, Greece

International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics 2015 (HOPV15)

Roma, Italy, 2015 May 11th - 13th

Organizer: Filippo De Angelis

Poster, Maria Vasilopoulou, 033
Publication date: 5th February 2015

Polyoxometalates (POMs), are a well-known large group of clusters with frameworks built from transition metal oxo anions linked by shared oxide ions, first reported by Jöns Jacob Berzelius in 1826. POM clusters are extraordinary molecules, because they have a high charge, are of nanoscale dimensions, and the framework cage can encapsulate many types of small templates while their molecular nature means they have a vast structural diversity, with many applications in areas such as catalysis and materials science. Previously, our group introduced the use of the Keggin phosphotungstic acid (PW₁₂O₄₀)^3-) as a novel electron injection/extraction layer in OLED/OPV devices, while, recently, POMs with the conventional Keggin structure have been also successfully incorporated by other groups as charge transport layers in organic solar cells. However, the question whether other members of the plethora of POM clusters may find application in organic optoelectronics and under what conditions has remained elusive. We report here on the preparation of electron conducting layers consisting of highly-reduced POM clusters (either Keggin or Dawson) deposited from a methanol solution between the OSC and Al electrode surfaces for application in organic optoelectronics. We observe that after the deposition of the metallic (Al) electrode onto a POM layer spontaneous electron transfer from Al to POM takes place causing the release of one to even six electrons, dependent on the position of the latter’s redox potential, that reduce the M (Mo, W, V) centers. The photoelectron spectroscopy reveals that the high degree of reduction introduces delocalized electrons that can hop over the M centers creating thus a highly conductive path permitting electrons to flow on and off the device and is therefore of vital importance in obtaining effective electron transport through the cathode interface. Our method is applicable to a wide range of different organic semiconducting materials and can also be used in most state-of-the-art high-efficiency organic electronic devices, including organic solar cells.

The project “Implementing advanced interfacial engineering strategies for highly efficient hybrid solar cells” is implemented under the "ARISTEIA II" Action of the "OPERATIONAL PROGRAMME EDUCATION AND LIFELONG LEARNING" and is co-funded by the European Social Fund (ESF) and National Resources

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