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We report the size- and temperature-dependence of electron transport in thin films of PbSe nanocrystals. Upon increasing temperature over the range 28–200 K, the electron transport underwent a transition in mechanism from Efros-Shklovskii-variable-range-hopping (ES-VRH) to nearest-neighbor-hopping (NNH). The transition occurred at higher temperatures for films with smaller particles. The electron localization length, estimated from the ES-VRH model, was comparable to the nanocrystal size and scaled systematically with nanocrystal diameter. The activation energy from the NNH regime was also size-dependent, which is attributed both to size-dependent Coulomb effects and the size-distribution of nanocrystals. [ABSTRACT FROM AUTHOR]

Electrical transport in films of CdSe nanocrystals with diameters varying from 2.9 to 5.1 nm was examined over 233−300 K by employing electrolyte gating to control the electron density. The transport parameters varied strongly and systematically with nanocrystal diameter. First, a strong correlation was observed between the device turn-on voltage and the size-dependent position of the lowest unoccupied electronic states of the nanocrystals. Second, the electron mobility increased with increasing particle diameter and reached a high value of 0.6 cm2/(V s) for films with 5.1 nm nanocrystals. Third, the charge transport could be described in terms of the nearest-neighbor-hopping mechanism with a size-dependent activation energy and a pre-exponential factor for mobility. The activation energy can be viewed as a size-dependent charging energy of an individual nanocrystal. Collectively, the combination of size- and temperature-dependent measurements provides a powerful approach to understanding electrical transport in nanocrystal films. [ABSTRACT FROM AUTHOR]