Long-Range Order in Nanocrystal Assemblies Determines Charge Transport of Films

Abstract

Self-assembly of semiconductor nanocrystals (NCs) into two-dimensional patterns or three-dimensional (2-3D) superstructures has emerged as a promising low-cost route to generate thin-film transistors and solar cells with superior charge transport because of enhanced electronic coupling between the NCs. Here, we show that lead sulfide (PbS) NCs solids featuring either short-range (disordered glassy solids, GSs) or long-range (superlattices, SLs) packing order are obtained solely by controlling deposition conditions of colloidal solution of NCs. In this study, we demonstrate the use of the evaporation-driven self-assembly method results in PbS NC SL structures that are observed over an area of 1 mm Ã\u97 100 μm, with long-range translational order of up to 100 nm. A number of ordered domains appear to have nucleated simultaneously and grown together over the whole area, imparting a polycrystalline texture to the 3D SL films. By contrast, a conventional, optimized spin-coating deposition method results in PbS NC glassy films with no translational symmetry and much shorter-range packing order in agreement with state-of-the-art reports. Further, we investigate the electronic properties of both SL and GS films, using a field-effect transistor configuration as a test platform. The long-range ordering of the PbS NCs into SLs leads to semiconducting NC-based solids, the mobility (μ) of which is 3 orders of magnitude higher than that of the disordered GSs. Moreover, although spin-cast GSs of PbS NCs have weak ambipolar behavior with limited gate tunability, SLs of PbS NCs show a clear p-type behavior with significantly higher conductivities

Deposition of Extended Ordered Ultrathin Films of Au38(SC2H4Ph)24 Nanocluster using Langmuir–Blodgett Technique

“…Nanoscale particles attract a lot of attention due to their size‐dependent optical, [ 1 ] electrical, [ 2,3 ] and chemical properties. [ 4,5 ] Of particular interest are ultrasmall metal nanoclusters (or clusters), which experience strong quantum confinement effect leading to profound changes in the atomic packing structure.…”

Rapid In Situ Ligand‐Exchange Process Used to Prepare 3D PbSe Nanocrystal Superlattice Infrared Photodetectors

“…A well-ordered 3D superlattice structure reduces positional disorder thereby increasing localization length, and is expected to correlate with higher carrier mobility and faster response compared to a disordered assembly. [18,22] With those challenges and concepts in mind, this paper has three objectives. First, we propose a hybrid strategy to perform one-step rapid ligand exchange through a solvated superlattice that preserves long-range order.…”

“…[20,21] The few reports that have successfully retained order after ligand exchange have improved carrier mobilities by approximately three orders of magnitude. [22] This paper describes a generalizable method for ordering semiconductor nanocrystal films and retaining that order during NC ligand exchange.…”

“…A well‐ordered 3D superlattice structure reduces positional disorder thereby increasing localization length, and is expected to correlate with higher carrier mobility and faster response compared to a disordered assembly. [ 18,22 ]…”

Complex Structures Resulting from Carboxylic Acid Self-Assembly: Comparison of 2-Naphthoic Acid to Quinaldic Acid and 3-Quinoline Carboxylic Acid

“…10,11 Additionally, self-assembly can be altered by the inclusion of various factors, including molecular functionalization, 12,13 charge separation, 14 and surface modification. 15 Self-assembly, along with the related fields of supramolecular chemistry and crystal engineering, has many practical applications including coatings, 16,17 nanoscale electronics, 18,19 and pharmaceuticals. 20,21 In planning and designing self-assembled systems, carboxylic acid (COOH) groups are a common supramolecular synthon: 22 a functional group with a powerful and reliable effect on self-assembly with performance that can be counted on largely independent of the rest of the molecule to which it is attached.…”