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Cherie Kagan1

1, University of Pennsylvania, Philadelphia, Pennsylvania, United States

Colloidal semiconductor nanocrystals (NCs) are prized for their size-dependent optical and electronic properties and for their solution-based processability that enables the integration of these materials in devices. However, the long, insulating ligands commonly employed in the synthesis of colloidal NCs inhibit strong interparticle coupling and charge transport once NCs are assembled to form NC solids. We employ a range of short, compact ligand chemistries to exchange the long, insulating ligands used in synthesis and to increase interparticle coupling.1 These ligand exchange processes can have a dramatic influence on NC surface chemistry as well as the organization of NCs in solids, showing examples of short-range order.2 Synergistically, we use 1) thermal evaporation and diffusion3,4 and 2) wet-chemical methods5 to introduce extrinsic impurities and non-stoichiometry that serve to passivate surface traps and dope NC solids. We show strong electronic coupling in combination with doping allows us to control the carrier type and concentration and to design high mobility n- and p-type materials. We give examples where n- and p-type semiconductor NC solids are used to construct flexible, electronic transistors and integrated circuits and optoelectronic solar photovoltaics and photodetectors.3,4,6,7 In combination with metal and insulating NCs, we demonstrate flexible, all-NC field-effect transistors.8

(1) Fafarman, A. T.; Koh, W.; Diroll, B. T.; Kim, D. K.; Ko, D.-K.; Oh, S. J.; Ye, X.; Doan-Nguyen, V.; Crump, M. R.; Reifsnyder, D. C.; Murray, C. B.; Kagan, C. R. J. Am. Chem. Soc. 2011, 133 (39), 15753–15761.
(2) Oh, S. J.; Wang, Z.; Berry, N. E.; Choi, J.-H.; Zhao, T.; Gaulding, E. A.; Paik, T.; Lai, Y.; Murray, C. B.; Kagan, C. R. Nano Lett. 2014, 14 (11), 6210–6216.
(3) Choi, J. H.; Fafarman, A. T.; Oh, S. J.; Ko, D. K.; Kim, D. K.; Diroll, B. T.; Muramoto, S.; Gillen, J. G.; Murray, C. B.; Kagan, C. R. Nano Lett. 2012, 12 (5), 2631–2638.
(4) Oh, S. J.; Berry, N. E.; Choi, J.-H.; Gaulding, E. A.; Paik, T.; Hong, S.-H.; Murray, C. B.; Kagan, C. R. ACS Nano 2013, 7 (3), 2413–2421.
(5) Oh, S. J.; Berry, N. E.; Choi, J.-H.; Gaulding, E. A.; Lin, H.; Paik, T.; Diroll, B. T.; Muramoto, S.; Murray, C. B.; Kagan, C. R. Nano Lett. 2014, 14 (3), 1559–1566.
(6) Stinner, F. S.; Lai, Y.; Straus, D. B.; Diroll, B. T.; Kim, D. K.; Murray, C. B.; Kagan, C. R. Nano Lett. 2015, 15 (10), 7155–7160.
(7) Oh, S. J.; Uswachoke, C.; Zhao, T.; Choi, J.-H.; Diroll, B. T.; Murray, C. B.; Kagan, C. R. ACS Nano 2015, 9 (7), 7536–7544.
(8) Choi, J.-H.; Wang, H.; Oh, S. J.; Paik, T.; Sung, P.; Sung, J.; Ye, X.; Zhao, T.; Diroll, B. T.; Murray, C. B.; Kagan, C. R. Science (80-. ). 2016, 352 (6282), 205–208.

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