Highly Conductive Copper Selenide Nanocrystal Thin Films for Advanced Electronics

Abstract

Investigation of the influence of the nanocrystal (NC) surface chemistry on the (opto)electronic properties of NCbased thin films is of paramount importance for their further application in various devices. In this work, macroscopic superlattices of copper selenide (Cu 2−x Se) NCs in the form of thin films were prepared by self-assembly at the liquid/air interface accompanied by simultaneous ligand exchange with the inorganic S 2− as well as organic 1,2-ethanedithiol, 1,4-butanedithiol, 1,6hexanedithiol, and 1,8-octanedithiol ligands. By using X-ray photoelectron spectroscopy and optical absorption spectroscopy, we revealed that the newly introduced ligands largely replaced the native surfactants on the Cu 2−x Se NC surface and acted as crosslinkers between neighboring particles. Transport measurements, specifically focusing on the interparticle distance, indicated 5− 9 orders of magnitude increase in electrical conductance with decreasing the size of the ligands from octanedithiol to inorganic sulfide ions, suggesting that the newly introduced species provide efficient and controllable electronic coupling for adjacent Cu 2−x Se NCs. Finally, the NC arrays were employed as chemiresistors to show the potential of these macroscopic superlattices in sensing applications.

InAs Nanocrystals with Robust p‐Type Doping

“…[21][22][23][24] The complexities in doping SC NCs are amplified by the possible differences in behavior of the isolated individual NCs, versus their characteristics in a working NC array in an electronically active device, where modifications of the surface chemistry are essential for effective interconnection to enable electrical transport among the nanocrystals. [25][26][27] Such surface modifications often affect the doping state and even the nature of doping on the level of the NC array. [26,[28][29][30][31][32] Indeed, "remote doping", through binding of electron donating groups, is a successful approach to electronically dope the NCs.…”

Tailoring the Surface Characteristics of CuSe Thin Films by Adjusting the Compositional Ratio

“…On the contrary, selenium, located below oxygen in the chalcogenide series in the periodic table of elements, shows higher metallicity and covalency than others. [ 1,5–7 ] Even though copper sulfide and copper selenide have similar structures, the electrical conductivity of copper selenide is higher than copper sulfide. [ 7 ]…”

“…[ 5 ] Also, the optical and electronic characteristics of copper selenide could be tuned depending on their crystalline structures and oxidation states of each element. [ 2,9 ] These materials can also have a variety of crystallographic forms that obey either stoichiometry rules (e.g., Cu 2 Se, CuSe, and Cu 3 Se 2 ) [ 1–3,5,7,10 ] or nonstoichiometry‐based compounds (e.g., Cu 2– x Se) [ 6,7,10 ] all under room temperature. Chen et al reported that copper selenide possessed a wide‐range of bandgaps: 1.1–1.5 eV for indirect bandgap [ 11,12 ] and 2.0–2.3 eV for direct bandgap, [ 11,13 ] which is dependent on the ratio of Se.…”

“…There are many routes to synthesize nanostructured materials and TFs, for example, electrodeposition, [ 1,3,7,10 ] spin coating, [ 5 ] self‐assembly, [ 6 ] chemical bath deposition, [ 11 ] and radio frequency (RF) cosputtering method. [ 14–16 ] Among them, RF cosputtering is a very useful method because TFs can be fabricated easily for industrial applications regardless of whether the material is an insulator, conductor, or semiconductor.…”

“…[ 17 ] Many researches have been conducted on the TFs involving one type of copper selenides. [ 3,5,6,10 ] However, only few studies have been reported on TFs with different compositional ratios of copper and selenide. Our group expected that the type of copper selenide being formed would depend on whether the TFs are Cu‐rich or Se‐rich would ultimately affect the surface properties.…”