Hydrogen Treatment as a Detergent of Electronic Trap States in Lead Chalcogenide Nanoparticles

Vörös, Márton; Brawand, Nicholas P.; Galli, Giulia

doi:10.1021/acs.chemmater.6b04126

Cited by 17 publications

(7 citation statements)

References 118 publications

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“…Constrained DFT Calculations : To assess charge hopping rates ( k CT ) between nanoflakes and reaction intermediates, CDFT calculations were performed, as implemented in the QUANTUM‐ESPRESSO code . The generalized gradient approximation of PBE as the exchange‐correlation functional was used .…”

Section: Methodsmentioning

confidence: 99%

New Class of Electrocatalysts Based on 2D Transition Metal Dichalcogenides in Ionic Liquid

et al. 2018

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electrochemical reactions. [1][2][3][4][5][6][7][8][9][10][11] In particular, molybdenum disulfide (MoS 2 ) and a few members of transition metal dichalcogenides (TMDCs) in contact with ionic-liquid (IL) electrolyte have recently shown a great promise to overcome fundamental electronic and thermokinetic limitations for CO 2 reduction reaction, as well as the oxygen reduction and evolution reactions (ORR/OER). [7][8][9][10] These studies have been conducted on a limited number of TMDCs, and the majority of other TMDCs with a wide range of electronic and potentially catalytic properties have not been investigated. In this study, we report synthesis and characterization of a wide range of TMDCs including sulfides, selenides, and tellurides of group V and VI transition metals and study their electrochemical performance in aprotic medium with Li salts. We employ a wide suite of characterization techniques, such as scanning transmission electron microscopy (STEM), energy dispersive spectroscopy (EDS), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), dynamic light scattering (DLS), and atomic forceThe optimization of traditional electrocatalysts has reached a point where progress is impeded by fundamental physical factors including inherent scaling relations among thermokinetic characteristics of different elementary reaction steps, non-Nernstian behavior, and electronic structure of the catalyst. This indicates that the currently utilized classes of electrocatalysts may not be adequate for future needs. This study reports on synthesis and characterization of a new class of materials based on 2D transition metal dichalcogenides including sulfides, selenides, and tellurides of group V and VI transition metals that exhibit excellent catalytic performance for both oxygen reduction and evolution reactions in an aprotic medium with Li salts. The reaction rates are much higher for these materials than previously reported catalysts for these reactions. The reasons for the high activity are found to be the metal edges with adiabatic electron transfer capability and a cocatalyst effect involving an ionic-liquid electrolyte. These new materials are expected to have high activity for other core electrocatalytic reactions and open the way for advances in energy storage and catalysis. ElectrocatalystsThe ORCID identification number(s) for the author(s) of this article can be found under https://doi.

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Section: Methodsmentioning

confidence: 99%

New Class of Electrocatalysts Based on 2D Transition Metal Dichalcogenides in Ionic Liquid

et al. 2018

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“…Density functional theory (DFT) calculations have led to an improved understanding of the origin of surface traps in QDs. 14 − 19 Recently, we have demonstrated that in undoped and charge-balanced nanocrystals only dicoordinated surface chalcogenide atoms should contribute to an electronic state within the band gap for zincblende II–VI nanocrystals. 20 This argument is ultimately based on orbital symmetry and can be expanded to other tetracoordinated (e.g., wurtzite) semiconductor QDs such as the III–V family and invites the prediction that the only requirement to achieve a trap-free QD should be a surface free of dicoordinated anions.…”

Section: Introductionmentioning

confidence: 99%

Finding and Fixing Traps in II–VI and III–V Colloidal Quantum Dots: The Importance of Z-Type Ligand Passivation

et al. 2018

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Energy levels in the band gap arising from surface states can dominate the optical and electronic properties of semiconductor nanocrystal quantum dots (QDs). Recent theoretical work has predicted that such trap states in II–VI and III–V QDs arise only from two-coordinated anions on the QD surface, offering the hypothesis that Lewis acid (Z-type) ligands should be able to completely passivate these anionic trap states. In this work, we provide experimental support for this hypothesis by demonstrating that Z-type ligation is the primary cause of PL QY increase when passivating undercoordinated CdTe QDs with various metal salts. Optimized treatments with InCl3 or CdCl2 afford a near-unity (>90%) photoluminescence quantum yield (PL QY), whereas other metal halogen or carboxylate salts provide a smaller increase in PL QY as a result of weaker binding or steric repulsion. The addition of non-Lewis acidic ligands (amines, alkylammonium chlorides) systematically gives a much smaller but non-negligible increase in the PL QY. We discuss possible reasons for this result, which points toward a more complex and dynamic QD surface. Finally we show that Z-type metal halide ligand treatments also lead to a strong increase in the PL QY of CdSe, CdS, and InP QDs and can increase the efficiency of sintered CdTe solar cells. These results show that surface anions are the dominant source of trap states in II–VI and III–V QDs and that passivation with Lewis acidic Z-type ligands is a general strategy to fix those traps. Our work also provides a method to tune the PL QY of QD samples from nearly zero up to near-unity values, without the need to grow epitaxial shells.

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“…Implementations of CDFT using plane‐wave basis sets appeared more recently, for instance in CPMD, [ 35,36 ] VASP [ 37 ] and CP2K (dual basis). [ 38 ] These plane‐wave implementations enabled CDFT calculations for condensed systems, and facilitated the study of important problems such as redox couples in aqueous solution, [ 35,39 ] charge transfer in biological molecules and proteins, [ 40 ] in quantum dots [ 41 ] and doped nanoparticles, [ 42 ] electron tunneling between defects [ 43 ] and polaron transport [ 44,45 ] in oxides, molecular solids, [ 40 ] and organic photovoltaic polymers [ 46 ] (see References [25] and [2] for extensive reviews). In existing implementations, DFT and CDFT are developed and maintained in the same code, thus requiring direct modifications of core DFT routines to support CDFT functionalities.…”

Section: Introductionmentioning

confidence: 99%

PyCDFT: A Python package for constrained density functional theory

Wang

Kim

et al. 2020

J Comput Chem

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We present PyCDFT, a Python package to compute diabatic states using constrained density functional theory (CDFT). PyCDFT provides an object‐oriented, customizable implementation of CDFT, and allows for both single‐point self‐consistent‐field calculations and geometry optimizations. PyCDFT is designed to interface with existing density functional theory (DFT) codes to perform CDFT calculations where constraint potentials are added to the Kohn–Sham Hamiltonian. Here, we demonstrate the use of PyCDFT by performing calculations with a massively parallel first‐principles molecular dynamics code, Qbox, and we benchmark its accuracy by computing the electronic coupling between diabatic states for a set of organic molecules. We show that PyCDFT yields results in agreement with existing implementations and is a robust and flexible package for performing CDFT calculations. The program is available at https://dx.doi.org/10.5281/zenodo.3821097.

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Hydrogen Treatment as a Detergent of Electronic Trap States in Lead Chalcogenide Nanoparticles

Cited by 17 publications

References 118 publications

New Class of Electrocatalysts Based on 2D Transition Metal Dichalcogenides in Ionic Liquid

New Class of Electrocatalysts Based on 2D Transition Metal Dichalcogenides in Ionic Liquid

Finding and Fixing Traps in II–VI and III–V Colloidal Quantum Dots: The Importance of Z-Type Ligand Passivation

PyCDFT: A Python package for constrained density functional theory

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