Giant Photoluminescence Enhancement in MoSe$_{2}$ monolayers treated with Oleic Acid Ligands

TL;DR

This study demonstrates that oleic acid treatment dramatically enhances photoluminescence in MoSe2 monolayers by passivating defects, leading to increased PL yield, spectral uniformity, and improved electronic properties.

Contribution

It introduces a simple oleic acid passivation method for MoSe2 monolayers, significantly boosting PL efficiency and reducing defects, which was previously unexplored for selenium-based TMDs.

Findings

PL yield increased by 58-fold after OA treatment

Enhanced spectral uniformity and reduced linewidth observed

Increased PL lifetime indicating trap-free exciton recombination

Abstract

The inherently low photoluminescence (PL) yields in as prepared transition metal dichalcogenide (TMD) monolayers are broadly accepted to be the result of atomic vacancies (i.e. defects) and uncontrolled doping, which give rise to non-radiative exciton decay pathways. To date, a number of chemical passivation schemes have been successfully developed to improve PL in sulphur based TMDs i.e. molybdenum disulphide (MoS2) and tungsten disulphide (WS2) monolayers. Reports on solution based chemical passivation schemes for improving PL yields in selenium (Se) based TMDs are lacking I comparison, with only one known study that uses hydrobromic acid vapour to improve PL in chemical vapour deposited (CVD) Molybdenum diselenide (MoSe2). Here, we demonstrate that treatment with oleic acid (OA) provides a simple wet chemical passivation method for monolayer MoSe2, enhancing PL yield by an average of 58 fold, while also enhancing spectral uniformity across the material and reducing emission linewidth. Excitation intensity dependent PL reveals trap-free PL dynamics dominated by neutral exciton recombination. Time-resolved PL (TRPL) studies reveal significantly increased PL lifetimes, with pump intensity dependent TRPL measurements also confirming trap free PL dynamics in OA treated MoSe2. Field effect transistors show reduced charge trap density and improved on-off ratios after treatment with OA. These results indicate defect passivation by OA, which we hypothesise act as ligands, passivating chalcogen defects through oleate coordination to Mo dangling bonds.