Surface Chemistry of CuInS₂ Colloidal Nanocrystals, Tight Binding of L-Type Ligands

Abstract

We analyze the surface chemistry of CuInS 2 nanocrystals synthesized in the presence of amines. Using solution NMR spectroscopy and elemental analysis, we come to the conclusion that as-synthesized CuInS 2 nanocrystals have charge neutral inorganic cores and are stabilized by a layer of tightly bound L-type amines. In situ NMR heating-up experiments show that desorption of amines can be induced by increasing the temperature, which makes the partial exchange of amines for thiols possible. On the other hand, we find that carboxylic acids are unable to bind as L-type ligands to the CuInS 2 surface. In addition, we demonstrate that the use of technical oleylamine in the synthesis of CuInS 2 nanocrystals leads to nonstoichiometric nanocrystals which have, next to oleylamine ligands, also X-type impurities on the surface that can be exchanged for carboxylic acids.

Solution-based synthesis and processing of Sn- and Bi-doped Cu3SbSe4nanocrystals, nanomaterials and ring-shaped thermoelectric generators

“…57 However, it was repeatedly reported that Cu-based NCs typically have tightly bound amines bound to the surface. 13,58 It should however be noted that OLA is quite easily desorbed during purification suggesting only a moderate binding affinity for the NC surface, in line with L-type ligand behaviour. To facilitate charge transport/transfer, CASe NCs were thoroughly purified by multiple precipitation/re-dispersion steps and subsequently treated with NH 4 SCN, which could efficiently displace remaining OLA.…”

Carboxylic‐Acid‐Passivated Metal Oxide Nanocrystals: Ligand Exchange Characteristics of a New Binding Motif

“…In apolar solvents,they coordinate to surface metal ions of stoichiometric NCs to yield overall charge-neutral objects. [5] Z-type ligands are neutral electron-pair acceptors (e.g., metal carboxylates) that bind to the surface anions of stoichiometric NCs. [1a] In NC surface chemistry,X-type ligands are presented as negatively charged ligands (RCOO À ,O H À ,C l À )t hat bind to excess surface cations of nonstoichiometric NCs.…”

Se-containing inks for the formation of CuInSe2 films without gas-phase selenization

“…In the case of CIS NCs, which are stabilized by OlAm after synthesis [21], addition of both NaHSe and (N 2 H 5 ) 2 Se to a polar phase in contact with the original apolar CIS dispersion leads to the transfer of the CIS NCs to the polar phase (see inset Fig. 4A).…”

“…As precursors, we focus on CuInS 2 (CIS) nanocrystals (NCs) synthesized by pyrolysis of metal organic precursors in an apolar solvent [21]. Similar NCs have been used before for the formation of CIGS solar cells by a process involving gas-phase selenization and yielding conversion efficiencies of up to 12% [22].…”