Heterovalent doping of halide perovskite nanocrystals (NCs), offering potential tunability in optical and electrical properties, remains a grand challenge. Here, we report for the first time a controlled doping of monovalent Ag+ into CsPbBr3 NCs via a facile room-temperature synthesis method. Our results suggest that Ag+ ions act as substitutional dopants to replace Pb2+ ions in the perovskite NCs, shifting the Fermi level down toward the valence band and in turn inducing a heavy p-type character. Field effect transistors fabricated with Ag+-doped CsPbBr3 NCs exhibit 3 orders of magnitude enhancement in hole mobility at room temperature, compared with undoped CsPbBr3 NCs. Low-temperature electrical studies further confirm the influence of Ag+ doping on the charge-carrier transport. This work demonstrates the tunability of heterovalent doping on the electrical properties of halide perovskite NCs, shedding light on their future applications in versatile optoelectronic devices.

We identify that reversible formation/decomposition of lithium oxide, pulverization of Fe 3 O 4 nanoparticles, and electrolyte reactions, are contributors to the enhanced capacity observed in the Fe 3 O 4 electrode upon long cycling. Introducing three-dimensional graphene foam to form a composite with Fe 3 O 4 nanoparticles largely increases the capacity (~1220 mA h g −1 vs.~690 mA h g −1) and promotes the cycling induced capacity enhancement (an earlier capacity rise and a faster rising rate) of the Fe 3 O 4 electrode. Together with Fe 3 O 4 nanoparticles, the presence of graphene effectively promotes the electrolyte reactions and reversible formation/ decomposition of lithium oxide. At the same time, activation of GF also occurs in the presence of Fe 3 O 4 nanoparticles, further increases the capacity of the nanocomposite.

In this work, an inverted device was fabricated using titania (TiO 2 ) as the electron collecting layer (ECL) and sulfonated poly(diphenylamine) (SPDPA) as the hole collecting layer (HCL). Smooth TiO 2 film with good electron collecting ability was easily formed using the spin-coating process. The power conversion efficiency (PCE) was 3.91%, the same as that of a conventional device. This inverted device is ascertained to maintain 2.82% PCE after 400 h of air-storage. Because of the appropriate work functions of ECL and HCL, the interfaces at the active layer have the ohmic contacts those approach the ideal value of open circuit voltage. SPDPA helps improve the interfacial dipole effect between the active layer and the metal, as verified by in-situ ultraviolet photoelectron spectroscopic data.

Improving devices based on solution-processed halide perovskite nanocrystals (NCs) demands a deeper understanding of charge transport in this emerging new class of ionic semiconductor nanomaterials. In this work, we fabricate all-inorganic CsPbBr3 NCs terminated with short ligands into field effect transistors, providing a facile platform to study the electronic–ionic transport systematically. By combining with transient response characterization, we demonstrate that electronic current is the dominant current passing through perovskite-NC films under dark conditions, while mobile ions induce intrinsic doping to perovskite NCs, which gradually changes the film conductivity and thereby the magnitude of the electronic current. The ion-induced doping prevails over the gating effect at room temperature, resulting in no gate modulation of the channel current in the transistor measurements. At T < 240 K, however, when ionic transport is suppressed, CsPbBr3-NC transistors exhibit a clean unipolar transport characteristic in a p-type mode featuring well-defined linear and saturation regimes. Extrinsically Bi3+- and Ag+-doped CsPbBr3-NC films further confirm the p-type transport property and dominant electrical gating effect at low temperature, which enables switching the device from normally off (p-type enhancement) to normally on (p-type depletion).

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