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CEMOS Report Summary

Project ID: 336506
Funded under: FP7-IDEAS-ERC
Country: Switzerland

Mid-Term Report Summary - CEMOS (Crystal Engineering for Molecular Organic Semiconductors)

Solution-processed organic photovoltaics (OPV) have recently reached the target 10% power conversion efficiency expected to signal their viable commercialization as an inexpensive and scalable energy conversion technology. However, obtaining devices with suitable long-term stability and tuned self-assembly remains an unsolved challenge. In the initial stages the CEMOS project we have demonstrated innovative methods of “bottom-up” crystal engineering for organic semiconductors. We have successfully prepared specifically tailored molecules designed to leverage both thermodynamic and kinetic aspects of molecular organic semiconductor systems to direct and control crystalline packing, promote crystallite nucleation, compatibilize disparate phases, and plasticize inelastic materials. In particular we have invented a new strategy to improve the thermal stability of small-molecule-based bulk-heterojunction OPVs by including a custom additive specifically designed to interact with the device active layer components ( Our results indicate that active layer degradation under continuous thermal stress can be inhibited due to the formation of more robust thin film microstructure with the additive present. Since our additive employs the identical semiconductor core used in the active layer, but linked by aliphatic chains into a flexible polymer, this straightforward strategy can reasonably be applied to stabilize a wide variety of semiconducting small molecules in solution-processed molecular OPVs, transistors and light emitting diodes. In addition, our flexible linker approach has led to give deep insights into how the crystalline packing—independent from the molecular structure—affects the charge transport (inter verses intra) in thin film active layers (see our preliminary work, which laid the groudwork for the project Expanding these initial results by refining the control of crystallinity and morphology of the active layer and furthering the understanding of the important aspects of device stability and performance is ongoing. In addition, our efforts have led to the discovery that n-type organic semiconductors can be employed as photoanodes for the direct conversion of sunlight into chemical fuel ( This demonstration suggests that robust organic semiconductors are suitable for direct photoelectrochemical water oxidation and opens a new path for the rational design and optimization of photoanodes for solar fuel production.

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