Bipolar shell resurfaced perovskite quantum dots

A quantum dot colloidal ink comprising:

• an organic solvent;
• and
• a plurality of perovskite quantum dots (QDs), the QDs composed of [M+]Pb[Ha−]3 and having outer surfaces covered in a sodium halide shell;
• wherein the halide anions in the shell occupy [Ha−] sites in the perovskite lattice, and the sodium cations are electrostatically bound to the fixed halide anions;
• wherein [M+] denotes a metal or organic cation with an oxidation state of +1 and each [Ha−] independently denotes any halide anion.

A semiconductor device comprising:

• an electroluminescent layer composed of a plurality of monodisperse halide perovskite quantum dots (QDs), the QDs composed of [M+]Pb[Ha−]3 wherein [M+] is a metal or organic cation with an oxidation state of +1 and [Ha−] is a halide anion;
• wherein the electroluminescent layer is substantially free of organic ligand molecules;
• and
• the mean interdot gap is less than 0.4 nm.

A method of forming a quantum dot light emissive layer comprising the step of:

• Solution processing onto a substrate a quantum dot colloidal ink comprising:
• an organic solvent;
• and
• a plurality of monodisperse halide perovskite quantum dots (QDs), the QDs composed of [M+]Pb[Ha−]3 and having outer surfaces covered in a sodium halide shell;
• wherein the halide anions in the shell occupy [Ha−] sites in the perovskite lattice, and the sodium cations are ionically bound to the fixed halide anions;
• wherein [M+] denotes a metal or organic cation with an oxidation state of +1 and each [Ha−] independently denotes any halide anion.