Palestrante
Descrição
Currently the most promising architecture for organic solar cells is the bulk heterojunction, which consists on dispersion of donor and acceptor molecules forming the active layer. (1) Aiming at advancing the fabrication of organic photovoltaic devices, we are investigating a new architecture based on a periodic arrangement of donor and acceptor molecules. They consist of polycrystalline metal-organic-frameworks assembled on a surface (SURMOFs) (2) where individual fullerene molecules (C60) are surrounded by a cage of donor molecules, like porphyrin derivatives (ZnTTP, in this case) that are complexed by metal cation centers. In a collaboration with a research team from the Karlshuer Institute of Technology (Germany), who provided the samples, we have used continuous-wave photoinduced absorption spectroscopy (cw-PA) to probe effective charge photogeneration on Surmofs. Measurements reveal a photoinduced absorption band in the near infrared due to long lived charged species that is assigned to π-π* transitions of the porphyrin cation (3), indicating that charge transfer from donor to acceptor (ZnTPP cation, C60 anion) can occur in SURMOFs. Modulation-frequency-dependent spectroscopy at 750 nm points that photogenerated charges have lifetime of 160 μs, while intensity-dependent data indicates that the charge recombination is mainly monomolecular. This suggests that charge migration throughout the SURMOFs is limited. Measurements under similar conditions were performed on well-established devices based on polymer bulk heterojunction P3HT:PCBM (fabricated in our group at IFSC), revealing that photoinduced charge generation efficiency is about 40 times higher than that on Surmofs, while the lifetime of photogenerated species is shorter. Discrepancy of charge photogeneration efficiency may be due to larger molecular spacing on Surmofs. Although these results point to a low efficiency of solar cells that would be fabricated by these SURMOFs, their wide variety of molecular architectures could be explored to eventually lead to efficient devices.
Referências
1 WONG, M. K.; WONG, K. Y. Investigation of the factors affecting the power conversion efficiency of all-solution-processed ‘bilayer’ P3HT:PCBM solar cells. Synthetic Metals, v. 170, p. 1-6, Apr. 2013. doi: 10.1016/j.synthmet.2013.02.021.
2 LIU, B. et. al. Chemistry of SURMOFs: layer-selective installation of functional groups and post-synthetic covalent modification probed by fluorescence microscopy. Journal of the American Chemical Society, v. 133, n. 6, p. 1734-1737, 2011.
3 GOUTERMAN, M. Spectra of porphyrins. Journal of Molecular Spectroscopy, v. 6, p. 138-163, 1961. doi: 10.1016/0022-2852(61)90236-3.
| Subárea | Física da Matéria Condensada |
|---|---|
| Apresentação do trabalho acadêmico para o público geral | Não |
