AmericanChemicalSociety.com

To make renewable energy sources economically competitive with burning fossil fuels, novel technological solutions for inexpensive fabrication of photovoltaic devices are required. Solution-based processes such as spin coating, dip coating, doctor blading and inkjet printing offer very substantial cost reductions for fabrication of electronic and optoelectronic devices. However, successful implementation of these techniques requires development of novel chemical approaches for solution-processed inorganic semiconductors.

Within the project funded by ACS Petroleum Research Fund we developed new chemistry for solution-based fabrication of inorganic functional materials from nanoscale building blocks. Specifically, we identified a very broad class of inorganic molecular species which can be used as surface ligands for almost all known colloidal metal and semiconductor nanostructures. Using this methodology, we synthesized novel nanostructured inorganic phases by combining colloidal inorganic semiconductor nanocrystals and molecular metal chalcogenide phases (so-called Zintl ions). During first year of funding we found that various molecular metal chalcogenide complexes, such as SnS₄^4-, Sn₂Se₆^4-, In₂Se₄^2-, Ge₄S₁₀^4- can be used to completely replace original hydrocarbon surface ligands at the surface of colloidal Au, CdS, CdSe and several other nanostructures. The great advantage of Zintl ions as the capping ligands for colloidal nanocrystals is the possibility to convert them into amorphous and crystalline metal chalcogenides with semiconducting properties, thus linking individual nano-building blocks into a macroscopic assembly of strongly electronically coupled functional modules. Our new chemistry sets new benchmarks for electronic coupling in self-assembled nanoparticle superlattices. For example, electrical conductivity of a superlattice of 6 nm Au nanocrystals with Sn₂S₆^4- ligands is about five orders of magnitude above the best previously reported numbers for Au nanoparticle arrays with conventional surface ligands. CdSe nanocrystals with Sn₂S₆^4- ligands showed good charge transport and high photoconductivity which are the important prerequisites for photovoltaic applications. This work has been published in Science Magazine.

We are currently working on extending this chemistry to nanostructured phases combining II-VI semiconductor nanocrystals and copper indium diselenide-based molecular metal chalcogenide complexes.