Investigation of ligand effects on exciton recombination in PbS nanoparticles

Abstract

Multiple exciton generation (MEG) and exciton recombination were studied by femtosecond transient absorption spectroscopy in PbS nanoparticles (NPs) capped with oleic acid (PbS–OLA) and 2,3-dimercaptopropane sulfonate (PbS–DMPS) ligands. Analysis of the transient absorption data showed that the PbS–DMPS nanoparticles exhibit increased rates of multi- and single-exciton recombination compared with the PbS–OLA nanoparticles; however, the MEG yield for both sets of particles was the same within experimental error. The origin of the differences in the exciton recombination decay rates is unknown, but it is speculated that it may be due to the ionic functionality of DMPS or to the different ligating atoms of the OLA and DMPS ligands. The PbS–DMPS nanoparticles were highly sensitive to the presence of oxygen, which caused a dramatic increase in nonradiative decay pathways, which can be mistaken for multiexciton absorbance and decay. Removal of oxygen eliminated the nonradiative decay pathways. Overall, this study showed that the dynamics of MEG can be modified by changing the NP ligand shell, a result that may be useful in the development of NP-based thin-film solar devices.

Charge Transport in Trap-Sensitized Infrared PbS Quantum-Dot-Based Photoconductors: Pros and Cons

“…In colloidal solutions, lead-chalcogenide QDs are commonly surrounded by long aliphatic ligands, which have a stabilizing and passivating role, allowing for flexible control over their size, shape, and composition [ 15 ] while preventing the formation of aggregates. Since ligands set the potential barrier for charge-carrier transfer and transport in QD solids, long insulating ligands must be replaced with shorter ones in order to enhance the coupling between QDs while still maintaining the carrier quantum confinement and efficiently passivating their surface [ 8 , 16 , 17 ]. Several ligand-exchange strategies were reported for lead-chalcogenide QDs, both in solution and in solid state, using bidentate thiols [ 18 ], primary amines [ 19 ], carboxylic acids [ 20 ], thiocyanate ions [ 21 ], and halide ions [ 2 ].…”

Synthesis of Iron-Phosphine Complexes Containing Sulfur Linking Groups for Coordination to PbS Nanoparticles

“…In this technique, an initial exchange is made using sodium 3-mercaptopropane-1-sulfonate (MPS) as a ligand shell transfer reagent [11] and then this ligand is exchanged by the desired ligand, in our case trans-FeCl 2 (DpPSMePE) 2 (2). Again, however, after repeated attempts the spectroscopic and TEM analyses gave no indication that the second exchange occurred.…”

A Biphasic Ligand Exchange Reaction on CdSe Nanoparticles: Introducing Undergraduates to Functionalizing Nanoparticles for Solar Cells

“…In these processes for low band gap ( E g ) semiconductor nanoparticles, one high energy photon (hυ ≥ 2 E g ) could produce more than one electron–hole pair, or exciton as seen in Figure . Due to strong confinement and the lack of lattice phonon coupling, MEG has been observed for many types of nanoparticles including lead and cadmium chalcogenides such as PbS, PbSe, PbTe, CdS, and CdSe. ,− Other instances of MEG have been reported for InAs, InGaAs, and silicon NP samples to name a few. ,− While there has been some controversy over the extent of reported MEG in NP systems, , any overproduction of charge carriers per photon absorbed could lead to improvements in efficiency of well-engineered NP-based photovoltaic cells.…”