Hypervalent surface interactions for colloidal stability and doping of silicon nanocrystals

Abstract

Colloidal semiconductor nanocrystals have attracted attention for cost-effective, solution-based deposition of quantum-confined thin films for optoelectronics. However, two significant challenges must be addressed before practical nanocrystal-based devices can be realized. The first is coping with the ligands that terminate the nanocrystal surfaces. Though ligands provide the colloidal stability needed to cast thin films from solution, these ligands dramatically hinder charge carrier transport in the resulting film. Second, after a conductive film is achieved, doping has proven difficult for further control of the optoelectronic properties of the film. Here we report the ability to confront both of these challenges by exploiting the ability of silicon to engage in hypervalent interactions with hard donor molecules. For the first time, we demonstrate the significant potential of applying the interaction to the nanocrystal surface. In this study, hypervalent interactions are shown to provide colloidal stability as well as doping of silicon nanocrystals.

Role of PbSe Structural Stabilization in Photovoltaic Cells

“…The results suggest that the passivation process acts as a preliminary exchange process at the nanocrystal surface, and this passivation displaces half of the oleate ligands prior to treatment with BDT. [ 76,77 ] Hence, we conclude that a large fraction of the native ligands are removed by BDT treatment, likely binding through a thiolate moiety, [66][67][68]76,77 ] in agreement with the earlier report on PbS. [ 7 ] In semiconductor NCs, surface defects can lead to nonradiative decay pathways that reduce the quantum effi ciency of the band edge PL.…”

“…[66][67][68] A large fraction of the atoms in a NC is at its surface, which is dynamic and crystallographically disordered. [ 34,[69][70][71] This structural disorder leads to disorder in the electronic structure of NCs immediately after synthesis, and Figure 1.…”

Postsynthetic Doping Control of Nanocrystal Thin Films: Balancing Space Charge to Improve Photovoltaic Efficiency

“…58,59 Direct donation of charge from ligands has also been observed for silicon nanoparticles capped with cholorine. 60 Interestingly, carrier concentrations in nanocrystal films are typically found to be much lower than expected if surface states and nonstoichiometry are the cause of doping. The effective doping concentration of a nanocrystal thin film arises from both the number of dopants per particle, and the number of particles per unit volume.…”

Plasmonic Properties of Silicon Nanocrystals Doped with Boron and Phosphorus

“…The most common strategies are the extrinsic doping of semiconductors with n-type or p-type dopants, 11-14 the self-doping of compound semiconductors through the tuning of the NC composition, 15,16 and the doping through NC-solvent interactions. 17 Doping of semiconductor NCs allows for control over the LSPR wavelength while the NC size or shape remain unaffected. However, like many nanomaterials, doped semiconductor NCs suffer from oxidation and the strong influence of the NC surface conditions which may negatively impact their plasmonic properties.…”