Charge transport mechanism in nanocrystal (NC) films is known to be very different from that in the bulk films. The charge transport in halide perovskite-NC films is further complicated due to the ionic nature of perovskites. In this work, we fabricate all-inorganic CsPbBr3 NCs terminated with short ligands into field effect transistors, which provides a facile platform to study the charge transport mechanism systematically. Using temperature and electric-field dependent transient response characterizations, we demonstrate that electronic current is the dominant current passing through perovskite-NC films under dark condition while mobile ions induce intrinsic doping to perovskite NCs, which gradually changes the conductivity and thereby the magnitude of the electronic current. At T < 240 K, when ionic transport is effectively suppressed, CsPbBr3-NC transistors exhibit a clean unipolar transport characteristic in a p-type mode featuring well-defined linear and saturation regime. Extrinsically Bi3+ and Ag+ doped CsPbBr3-NC films further confirms the p-type transport property and dominant gate effect which enables switching the device from normally off (p-type enhancement) to normally on (p-type depletion). Our study suggests a different interplay mechanism between ionic transport and electronic transport in perovskite NC films, compared with that observed in perovskite bulk films. The localization of ion transport within the NCs could weaken the ionic screening effect while strengthen the doping effect, encouraging the design of novel perovskite-NC-based devices through both intrinsic and extrinsic doping.
Manuscript by Zhou et al. was published at ACS Energy Letters, 2020, 5, 2614−2623, https: https://pubs.acs.org/doi/abs/10.1021/acsenergylett.0c01295