Control Over Metal-Halide Reactivity Enables Uniform Growth of InSb Colloidal Quantum Dots for Enhanced SWIR Light Detection

InSb colloidal quantum dots (CQDs) hold promise in short-wave infrared sensing; however, their synthesis presents ongoing challenges, particularly in achieving precise size control – this is the result of poorly controlled reactivity among the precursors. Herein, the use of alkyl-phosphine and amine-based organic additives to control the reactivity of In and Sb precursors during the nucleation and growth of CQDs is developed. This interplay between organic additive and precursors enables the synthesis of InSb CQDs having narrowed size distributions; and bandgaps tunable across the 1.2–1.5 µm spectral range; all this leading to peak-to-valley ratios >1.4 in absorption spectra. The CQDs are surface-terminated with a mixture of oleylamine, halides, and oxide-like species, and this hinders ligand exchange reactions and subsequent integration into photodiodes. We therefore resurface the CQDs with alkanethiols, displacing the native ligands via an acid-base mechanism, an approach that removes oxide species. Using a layer-by-layer fabrication process, the ligands of the resurfaced InSb CQDs are exchanged with short organic and halide ligands and incorporated films into n-i-p photodiode structures. The resultant devices exhibit a detectivity of 10¹² Jones, an external quantum efficiency (EQE) of 33% at 1380 nm, and T₉₀ operating stability of >19 h under continuous illuminated operation.