Assembled Monolayer Nanorod Heterojunctions

Abstract

Compositional and interfacial control in heterojunction thin films is critical to the performance of complex devices that separate or combine charges. For high performance, these applications require epitaxially matched interfaces, which are difficult to produce. Here, we present a new architecture for producing low-strain, single-crystalline heterojunctions using self-assembly and in-film cation exchange of colloidal nanorods. A systematic set of experiments demonstrates a cation exchange procedure that lends precise control over compositional depths in a monolayer film of vertically aligned nanorods. Compositional changes are reflected by electrical performance as rectification is induced, quenched, and reversed during cation exchange from CdS to Cu(2)S to PbS. As an additional benefit, we achieve this single-crystal architecture via an inherently simple and low-temperature wet chemical process, which is general to a variety of chemistries. This permits ensemble measurement of transport through a colloidal nanoparticle film with no interparticle charge hopping.

Perovskite Materials for Light‐Emitting Diodes and Lasers

“…Cation substitution is used as a common strategy to change the color emission, e.g., Ag 2 Se NPs and PbS NRs from CdSe NPs and CdS NRs, respectively. [96,97] Similar to the halide exchange in perov skites, [75,76] the pre-existing morphology can be preserved after cation substitution. Cation substitution of CsPbBr 3 NPs with CH 3 NH 3 + cations from methylammonium bromide (MA-Br) [75] resulted in a PL shift from 510.2 to 525.4 nm, similar to the PL value (527 nm) observed for CH 3 NH 3 PbBr 3 .…”

Cation Exchange: A Versatile Tool for Nanomaterials Synthesis

“…31 Performing the Cu + exchange on selfassembled, aligned CdS nanorods can be used to further increase the asymmetry of this exchange, forming nanorods with a single interface Cu 2 S−CdS primed for directional charge separation and extraction. 60 Likewise, binary nanorod superlattices can be formed by partial Ag + exchange of CdS nanorods, 30 and these complex heterostructure morphologies can be further elaborated to generate divalent metal chalcogenide superlattices via two sequential ion substitutions. 27 Heterostructures analogous to seeded rods but composed of two different cations within a common anion sublattice can also be synthesized via partial exchange.…”

Au2Sx/CdS Nanorods by Cation Exchange: Mechanistic Insights into the Competition Between Cation‐Exchange and Metal Ion Reduction

“…[ 12,16 ] Preservation of anionic framework during cation exchange [ 17,18 ] enables synthesis of multicomponent heterostructures with enhanced level of control over morphology and chemistry. [ 19 ] Site specifi city of the exchange reaction gives rise to several interesting possibilities of nanostructuring including Ag 2 S bar-coding in CdS, [ 20 ] formation of Cu 2 S on the tip of CdS nanorods [ 21,22 ] and multipodal structures. [ 23 ] In spite of its signifi cant advantages, one of the primary limitations of cation exchange is that the metals with higher electron affi nity tend to undergo reduction rather than cation exchange, thus making the process very system specifi c. [ 20 ] This competition between cation exchange and reduction is not well understood.…”