Optical Properties, Morphology, and Stability of Iodide-Passivated Lead Sulfide Quantum Dots.

Ivan D Skurlov,Alexander V Baranov,Anastasiia S Mudrak,Aliaksei Dubavik,Iurii G Korzhenevskii,Aleksandr P Litvin,Petr S Parfenov,Xiaoyu Zhang,Sergei A Cherevkov,Anatoly V Fedorov

doi:10.3390/ma12193219

Abstract

Iodide atomic surface passivation of lead chalcogenides has spawned a race in efficiency of quantum dot (QD)-based optoelectronic devices. Further development of QD applications requires a deeper understanding of the passivation mechanisms. In the first part of the current study, we compare optics and electrophysical properties of lead sulfide (PbS) QDs with iodine ligands, obtained from different iodine sources. Methylammonium iodide (MAI), lead iodide (PbI2), and tetrabutylammonium iodide (TBAI) were used as iodine precursors. Using ultraviolet photoelectron spectroscopy, we show that different iodide sources change the QD HOMO/LUMO levels, allowing their fine tuning. AFM measurements suggest that colloidally-passivated QDs result in formation of more uniform thin films in one-step deposition. The second part of this paper is devoted to the PbS QDs with colloidally-exchanged shells (i.e., made from MAI and PbI2). We especially focus on QD optical properties and their stability during storage in ambient conditions. Colloidal lead iodide treatment is found to reduce the QD film resistivity and improve photoluminescence quantum yield (PLQY). At the same time stability of such QDs is reduced. MAI-treated QDs are found to be more stable in the ambient conditions but tend to agglomerate, which leads to undesirable changes in their optics.

Highlights

Type of the ligand and exchange treatment procedure govern quantum dot (QD) solid properties, such as energy structure, charge transport, and stability [1,2]
We show that the use of methylammonium iodide (MAI), lead iodide (PbI2 ), and tetrabutylammonium iodide (TBAI) have both advantages and disadvantages, indicating that a careful choice of both the ligand exchange (LE)
LE efficiency was estimated by monitoring the residual oleic acid (OA) ligands on the QD surface using the Fourier-transformed infrared (FTIR) spectroscopy

Summary

Introduction

Type of the ligand and exchange treatment procedure govern quantum dot (QD) solid properties, such as energy structure, charge transport, and stability [1,2]. Commonly used in organometallic QD synthesis, lead to large interdot distances after the film deposition. Due to such distances, dot-to-dot coupling is reduced and charge transfer between QDs vanishes [3]. QD film acts as an insulator, preventing its application as an active layer in optoelectronic devices. One of the ways to increase QD coupling is to reduce interdot spacing by ligand stripping or ligand exchange (LE). During LE, it is possible to reduce the number of surface defects responsible for non-radiative carrier losses

Methods

Results

Conclusion