Colloidal CuInSe₂ nanocrystals: From gradient stoichiometry toward homogeneous alloyed structure mediated by conducting polymer P3HT

We report, for the first time, the synthesis of colloidal copper indium selenide (CuInSe₂) nanocrystals (NCs) possessing a gradient stoichiometry that is potentially tunable by the presence of a conducting polymer, i.e., poly(3-hexyl thiophene) (P3HT) in the synthesis medium. Dibenzyl ether (DBE) was used as a reaction medium, whereas copper acetylacetonate (Cu(acac)₂), indium acetylacetonate (In(acac)₃), and selenium powder were used as Cu, In, and Se sources, respectively. The Se precursor was tri-n-octylphosphine selenide (TOP-Se). Without the presence of P3HT, the resulting NCs consist of a p-type (Cu¹⁺ rich) core and an n-type (In³⁺ rich) shell. Such a gradient stoichiometry was moderated to be substantially more homogeneous because the presence of P3HT is believed to have significantly reduced the reactivity difference between Cu(acac) ₂ and In(acac)₃, as well as and their respective monomers. Furthermore, the P3HT also acts as a surface coordination species, contributing to the readily preparation of conducting polymer-NCs hybrids by a single-step synthesis. The understandings of this work can serve as a guide for design and synthesis of conducting polymer-NCs hybrids based on various ternary or quaternary compound semiconductors with different core-shell composition gradient.