Oleylamine (OLA) is a ubiquitous organic ligand used in the synthesis of inorganic nanocrystals (NCs) due to its ability to reduce metal precursors and sterically stabilize NCs. However, attempts to thermally remove the ligand from deposited OLA-capped NC films result in ligand pyrolysis, where the organic residue is ultimately embedded into the active material as a carbon defect. Herein, we investigated the thermal decomposition and restructuring of OLA ligands using a combination of Raman spectroscopy and X-ray photoelectron spectroscopy (XPS), seeking to determine the specific nature of OLA’s decomposition and reasons for its ultimate incorporation into a carbon-rich fine-grain layer observed in Cu2ZnSn­(S1–x Se x )4 (CZTSSe) systems. While it has historically been expected that OLA pyrolyzes during thermal treatments, this work identifies that OLA decomposes into nanostructured graphitic carbon, which is first detectable immediately after the NC synthesis at 225 °C, well before the employment of thermal treatments. These graphitic flakes are further identified as disordered graphene oxide, which segregates from OLA-capped NCs during deposition to assemble into the carbon-rich layer. In identifying that the carbon-rich fine-grain layer originates prior to thermal treatments, we introduce a strategy to partially reduce the presence of this layer by isolating the graphene oxide flakes immediately after the CZTS NC synthesis.

Inorganic–organic interfaces: a tutorial on using organic functional groups to enhance the performances and/or enable new functionality of inorganic nanomaterials.

Aliphatic amine and carboxylic acid ligands are widely used as organic solvents during the bottom-up synthesis of inorganic nanoparticles (NPs). Although the ligands’ ability to alter final NP properties has been widely studied, side reactivity of these ligands is emerging as an important mechanism to consider. In this work, we study the thermal decomposition of common ligands with varying functional groups (amines and carboxylic acids) and bond saturations (from saturated to polyunsaturated). Here, we investigate how these ligand properties influence decomposition in the absence and presence of precursors used in NP synthesis. We show that during the synthesis of inorganic chalcogenide NPs (Cu 2 ZnSnS 4 , Cu x S, and SnS x ) with metal acetylacetonate precursors and elemental sulfur, the ligand pyrolyzes, producing alkylated graphitic species. Additionally, there was less to no ligand decomposition observed during the sulfur-free synthesis of ZnO and CuO with metal acetylacetonate precursors. These results will help guide ligand selection for NP syntheses and improve reaction purity, an important factor in many applications.

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