Alteration of the Optoelectronic Properties of CuInS₂ Quantum Dots via Colloidal Annealing

Abstract

Colloidal semiconductor quantum dots (QDs) have tunable optoelectronic properties, thereby making them interesting materials for applications involving light-matter interactions. However, crystallographic and surface defects greatly impair their potential performance in devices. Herein, we present a straightforward approach to improve the quality of copper indium disulfide (CuInS 2 ) QDs by adjusting the parameters of the colloidal synthesis. By the introduction of prolonged heating times after the nanocrystal growth has already gone to completion, defect states are partially removed. This "colloidal annealing" for varying time spans (from 5 up to 90 min) with longer annealing times correlating with a decreased ratio of emission from defect states compared to band edge emission, results in enhanced color purity. At shorter annealing times, the defects removed are mainly structural, indicated by the transition from mixed crystal phases to an almost phase-pure material. At longer annealing times, further improvements are linked to surface defect removal. Findings from transient absorption spectroscopy further confirm this trend by revealing a decrease in the intensity of a photoinduced absorption feature associated with sub-band gap states compared to the band edge bleach signal. These findings highlight the applicability of colloidal annealing as a straightforward strategy for direct material optimization during colloidal synthesis.

Unravelling the intricacies of solvents and sulfur sources in colloidal synthesis of metal sulfide semiconductor nanocrystals

“…73 The most used thiols in nanoparticle synthesis are 1-dodecanethiol (DDT) and tert -dodecanethiol. 74–78 While 1-dodecanethiol has 12 carbons linearly attached to its thiol group, tert -dodecanethiol has also 12 carbons but the alpha carbon is ternary. The long alkane chain in both thiols gives them high boiling points, which makes them also good candidates for solvents and good surface ligands in nanoparticle synthesis.…”