Room‐Temperature Cation‐Exchange Synthesis of PbS Colloidal Quantum Dots in Polar‐Solvent for High‐Performance Near Infrared Optoelectronic Devices

ABSTRACT PbS colloidal quantum dots (CQDs) have attracted significant attention as light sources and photodetectors in the second near‐infrared (NIR‐II) window for optical communication, bioimaging, and night vision. Recently, a room‐temperature direct synthesis of PbS CQD inks has been developed, enabling low‐cost and large‐scale fabrication of QD optoelectronic devices. However, the synthesis of high‐quality large‐sized CQDs with photoluminescence (PL) peaks beyond 1550 nm remains challenging. In this work, we developed a novel room‐temperature cation‐exchange synthesis strategy in a polar solvent system. Distinct from existing approaches, the strategy employs ZnS nanoseeds as the sulfur precursor, enabling tunable PL peaks in the range of 1050–1650 nm by precisely controlling the reaction kinetics. The in situ passivation by Zn cations and acetate anions effectively reduces surface defects on the nonpolar (100) facets. Based on this strategy, we fabricated near‐infrared II (NIR‐II) light‐emitting diodes (LEDs) exhibiting a maximum radiance of 22.15 W sr −1 m −2 , together with a record‐breaking critical current density for external quantum efficiency (EQE) roll‐off ( J 1/2EQE = 3.4 A cm −2 ). Furthermore, NIR‐II photodetectors demonstrate a high photoresponsivity of 0.68 A W −1 and a specific detectivity of 1.12 × 10 11 Jones at 1490 nm.