Ligand-exchange-assisted printing of colloidal nanocrystals to enable all-printed sub-micron optoelectronics.

Additive manufacturing enables customised device fabrication for emerging sensing technologies. However, printable (opto)electronic devices with sophisticated architectures, including all-printed photodiodes, face challenges in multi-material and multi-layer printing at micro- and nanoscales with low processing temperatures. Herein, we establish a nano-resolution printing method based on electrohydrodynamic printing (EHDP) to deposit inks from the colloidal nanocrystal (NC) library, followed by in situ room-temperature ligand exchange to functionalise the NC solids. This general approach enables layer-by-layer printing with wide selections of NC inks, ligand reagents, substrates, and device architectures. Chemical-treatment-induced contraction and densification grants printed Ag NC structures electrical conductivity and an achievable feature size and filling ratio of 70 nm and 75%, respectively, constructing wide-gamut structural colour gratings. By exploiting Ag, Au, PbS, and ZnO NCs and compact ligands, we demonstrate all-printed multi-layer infrared photodiodes with sub-10-µm pixel sizes. The nano-printing assembly of hetero-NCs promises the facile integration of multi-functional micro-nano devices.