Advances in synthetic methods allow a wide range of semiconductor nanocrystals (NCs) to be tailored in size and shape and to be used as building blocks in the design of NC solids. However, the long, insulating ligands commonly employed in the synthesis of colloidal NCs inhibit strong interparticle coupling and charge transport once NCs are assembled into the solids state as NC arrays. We employ a range of short, compact ligand chemistries to exchange the long, insulating ligands used in synthesis and to increase interparticle coupling. These ligand exchange processes can have a dramatic influence on NC surface chemistry as well as NC organization in the solids, showing examples of short-range order. Synergistically, we use 1) thermal evaporation and diffusion and 2) wet-chemical methods to introduce extrinsic impurities and non-stoichiometry to passivate surface traps and dope NC solids. NC coupling and doping provide control over the density of states, the carrier statistics and the Fermi energy. Examples of strong coupling and doping in II-VI and IV-VI semiconductor NC solids will be given that yield high-mobility, high-conductivity solution-deposited NC solids. Temperature--dependent transport measurements of these materials are consistent with a transition from localized to extended-state charge transport. These high mobility n- and p-type materials are used as the semiconductors to construct large-area, flexible, field-effect transistors and integrated circuits and for solar photovoltaics.

Designer semiconductor nanocrystal electronic and optoelectronic materials and devices

249th National Meeting (2015)

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