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In 2008-2009, with partial support from ACS Petroleum Research Fund, we have developed novel methodology for design of solution-processed semiconductors for photovoltaic and thermoelectric applications. Specifically, we reported a very broad class of inorganic molecular species, molecular metal chalcogenide complexes (MCCs), that can be used as the “electronic glue” for different colloidal metal and semiconductor nanostructures [¹] This was a paradigm shifting approach because in traditional nanocrystal assemblies individual particles are separated by insulating or poorly conducting organic ligands. The use of inorganic molecular linkers (i) provided much more efficient charge transfer between individual nanostructures and (ii) enabled carbon-free materials design and high stability under realistic photovoltaic or photochemical operational conditions. The work supported through ACS Petroleum Research Fund in 2009 has resulted in one publication:

M.V. Kovalenko, M. Scheele, D.V. Talapin, Colloidal Nanocrystals with Molecular Metal Chalcogenide Surface Ligands. Science 324, 1417-1420 (2009).

In 2010 we continued working on this topic and and demonstrated the possibility of designing truly high-performance solution-processed semiconductors. Thus, our MCC ligands set new benchmarks for electrical conductivity and electron mobility in the nanocrystal solids. Spin-coated arrays of CdSe nanocrystals capped with In₂Se₄^4- ligands now reproducibly exhibit room temperature electron mobility 12-16 cm²V^-1s^-1 which is at least one order of magnitude higher than the carrier mobility in best solution-processed organic [²] and nanocrystal-based [³] materials. Further increase of the carrier mobility might be possible by further process optimization. I am not aware of any other approach that could provide a dense film of a direct gap semiconductor with comparable carrier mobility via a simple low temperature solution-based route. Moreover, our high mobility nanocrystal solids preserved the properties of quantum-confined semiconductors. High carrier mobility, combined with size-tunable electronic structure, makes MCC-capped nanocrystals very attractive for printable photovoltaics. By selecting nanocomponents and MCC ligands we gain the flexibility to provide an impressive library of materials.

The work supported through ACS Petroleum Research Fund in 2010 has resulted in two publications:

1.      D. V. Talapin, J.-S. Lee, M. V. Kovalenko, E. V. Shevchenko, Prospects of Nanocrystal Solids as Electronic and Optoelectronic Materials. Chem. Rev. 110, 389–458 (2010).

2.      J.-S. Lee, M. V. Kovalenko, J. Huang, D. V. Talapin, High electron mobility and photoconductivity in arrays of CdSe and CdSe/CdS nanocrystals bridged with molecular metal chalcogenide ligands Submitted to Nature Nanotechnology.

Several other publications may follow in the near future.

Cited literature:

1.         Kovalenko, M.V., Scheele, M.,  Talapin, D.V., Colloidal Nanocrystals with Molecular Metal Chalcogenide Surface Ligands. Science 324, 1417-1420 (2009).

2.         Coropceanu, V., Cornil, J., da Silva Filho, D.A., Olivier, Y., Silbey, R.,  Bredas, J.-L., Charge Transport in Organic Semiconductors. Chem. Rev. 107, 926-952 (2007).

3.         Talapin, D.V., Lee, J.-S., Kovalenko, M.V.,  Shevchenko, E.V., Prospects of Colloidal Nanocrystals for Electronic and Optoelectronic Applications. Chem. Rev. 110, 389-458 (2010).