Radiation damage in biomimetic dye molecules for solar cells

Abstract

A significant obstacle to organic photovoltaics is radiation damage, either directly by photochemical reactions or indirectly via hot electrons. Such effects are investigated for biomimetic dye molecules for solar cells (phthalocyanines) and for a biological analog (the charge transfer protein cytochrome c). Both feature a central transition metal atom (or H(2)) surrounded by nitrogen atoms. Soft x-ray absorption spectroscopy and photoelectron spectroscopy are used to identify three types of radiation-induced changes in the electronic structure of these molecules. (1) The peptide bonds along the backbone of the protein are readily broken, while the nitrogen cage remains rather stable in phthalocyanines. This finding suggests minimizing peptide attachments to biologically inspired molecules for photovoltaic applications. (2) The metal atom in the protein changes its 3d electron configuration under irradiation. (3) The Fermi level E(F) shifts relative to the band gap in phthalocyanine films due to radiation-induced gap states. This effect has little influence on the optical absorption, but it changes the lineup between the energy levels of the absorbing dye and the acceptor/donor electrodes that collect the charge carriers in a solar cell.

Electronic structure of Fe- vs. Ru-based dye molecules

“…This suggests searching for dye molecules containing Fe in similar octahedral cages, but without the protein backbone which is fragile and prone to radiation damage. 49,50 This avenue will be pursued further in a separate publication. 51 Overall, this research is part of a program to measure the energy levels relevant to the performance of solar cells.…”

Modified Au-Based Nanomaterials Studied by Surface Plasmon Resonance Spectroscopy

“…20 Una vez desarrollado el dispositivo experimental SPR-XAS, la espectroscopía de SPR es usada para estudiar cambios en elíndice de refracción inducidos mediante rayos X en vidrios y en CoPcs, ya que en muchas ocasiones es necesario que estos materiales respondan correctamente bajo radiación. [17][18][19] Para el caso del estudio de los vidrios, películas de Au son crecidas sobre dos tipos de substratos de vidrio: substratos sodicocálcicos y de sílice.…”

“…Estas modificaciones deĺ ındice de refracción no son relacionadas con cambios estructurales y son asociadas con modificaciones electrónicas inducidas por la irradiación. 19 Las principales conclusiones extraídas de este trabajo son:…”

“…These modifications of the refractive index are not related to structural changes and they are associated with electronic modifications induced by the irradiation. 19 The main conclusions related to this work are:…”

“…[15][16][17][18][19] The combination of both techniques, to our knowledge, has never been achieved. Thus, in this work, we have designed and developed a setup combining SPR and XAS: the SPR-XAS setup, which allows different types of measurements in situ and in real time, recording SPR or XAS signals while scanning other parameters such as time, energy, etc.…”