Role of Pb2+ Adsorbents on the Opto-Electronic Properties of a CsPbBr3 Nanocrystal: A DFT Study

MRS Advances ◽  
2019 ◽  
Vol 4 (36) ◽  
pp. 1981-1988
Author(s):  
Aaron Forde ◽  
Erik Hobbie ◽  
Dmitri Kilin
Keyword(s):  
Electronic Properties ◽  
Density Functional ◽  
Surface Defects ◽  
Energy Transition ◽  
Conduction Band Edge ◽  
Trap States ◽  
Functional Theory ◽  
Light Emitting ◽  
Light Emitting Devices

ABSTRACTFully inorganic lead halide perovskite nanocrystals (NCs) are of interest for photovoltaic and light emitting devices due to optoelectronic properties. Understanding the surface chemistry of these materials is of importance as surface defects can introduce trap-states which reduce their functionality. Here we use Density Functional Theory (DFT) to model surface defects introduced by Pb2+ on a CsPbBr3 NC atomistic model. Two types of defects are studied: (i) an under-coordinated Pb2+ surface atom and (ii) Pb2+ atomic or molecular adsorbents to the NC surface. From the DFT calculations we compute the density of states (DOS) and absorption spectra of the defect models to the pristine fully-passivated NC model. We observe that for the low surface defect regime explored here that neither (i) or (ii) produce trap-states inside of the bandgap and exhibit bright optical absorption for the lowest energy transition. From the models studied, it was found that the Pb2+ atomic absorbent provides broadening of the conduction band edge, which implies chemisorption of Pb2+ to the NC surface. At higher defect densities it would be expected that Pb2+ atomic absorbents would introduce trap-states and degrade the opto-electronic properties of these materials.

scholarly journals Strain-induced effects on the electronic properties of 2D materials

2020 ◽  
Vol 10 ◽  
pp. 184798042090256 ◽  
Author(s):  
Sara Postorino ◽  
Davide Grassano ◽  
Marco D’Alessandro ◽  
Andrea Pianetti ◽  
Olivia Pulci ◽  
...  
Keyword(s):  
Electronic Properties ◽  
Density Functional ◽  
2D Materials ◽  
Transition Metal Dichalcogenides ◽  
Many Body ◽  
Functional Theory ◽  
Metal Dichalcogenides ◽  
Extreme Sensitivity ◽  
Nonuniform Strain

Thanks to the ultrahigh flexibility of 2D materials and to their extreme sensitivity to applied strain, there is currently a strong interest in studying and understanding how their electronic properties can be modulated by applying a uniform or nonuniform strain. In this work, using density functional theory (DFT) calculations, we discuss how uniform biaxial strain affects the electronic properties, such as ionization potential, electron affinity, electronic gap, and work function, of different classes of 2D materials from X-enes to nitrides and transition metal dichalcogenides. The analysis of the states in terms of atomic orbitals allows to explain the observed trends and to highlight similarities and differences among the various materials. Moreover, the role of many-body effects on the predicted electronic properties is discussed in one of the studied systems. We show that the trends with strain, calculated at the GW level of approximation, are qualitatively similar to the DFT ones solely when there is no change in the character of the valence and conduction states near the gap.

Theoretical Study of the Electronic Structure and Properties of Alternating Donor-Acceptor Couples of Carbazole-Based Compounds for Advanced Organic Light-Emitting Diodes (OLED)

2019 ◽  
Vol 824 ◽  
pp. 236-244
Author(s):  
Suppamat Makjan ◽  
Malinee Promkatkaew ◽  
Supa Hannongbua ◽  
Pornthip Boonsri
Keyword(s):  
Density Functional Theory ◽  
Electronic Properties ◽  
Density Functional ◽  
Light Emitting Diodes ◽  
Functional Theory ◽  
Light Emitting ◽  
Organic Light ◽  
Hole Transporting ◽  
Photorefractive Materials ◽  
Donor Acceptor

Generally, it is difficult to generate a high-performance pure blue emission organic light-emitting diode (OLED). That is because the intrinsically wide band-gap makes it hard to inject charges into the emitting layer in such devices. To solve the problem, carbazole derivatives have been widely used because they have more thermal stability, a good hole transporting property, more electron rich (p-type) material, and higher photoconductivity. In the present work, novel copolymers containing donor-acceptor-acceptor-donor (D-A-A-D) blue compounds used for OLEDs were investigated. The theory of the geometrical and electronic properties of N-ethylcarbazole (ECz) as donor molecule (D) coupled to a series of 6 acceptor molecules (A) for advanced OLEDs were investigated. The acceptors were thiazole (TZ), thiadiazole (TD), thienopyrazine (TPZ), thienothiadiazole (TTD), benzothiadiazole (BTD), and thiadiazolothienopyrazine (TDTP). The ground state structure of the copolymers were studied using Density Functional Theory (DFT) at B3LYP/6-31G(d) level. Molecular orbital analysis study indicated 3 investigated copolymers (ECz-diTZ-ECz, ECz-diTD-ECz, ECz-diBTD-ECz) have efficient bipolar charge transport properties for both electron and hole injection to the TiO2 conduction band (4.8 eV). In addition, the excited states electronic properties were calculated using Time-Dependent Density Functional Theory (TD-DFT) at the same level. Among these investigated copolymer ECz-diTZ-ECz and ECz-diTD-ECz showed the maximum absorption wavelengths (λabs) with blue emitting at 429 and 431 nm, respectively. The results suggested that selected D-A-A-D copolymers can improve the electron- and hole- transporting abilities of the devices. Therefore, the designed copolymers would be a promising material for future development of light-emitting diodes, electrochromic windows, photovoltaic cells, and photorefractive materials.

Narrow bandgap covalent–organic frameworks with strong optical response in the visible and infrared

2015 ◽  
Vol 3 (10) ◽  
pp. 2244-2254 ◽  
Author(s):  
Li-Ming Yang ◽  
Eric Ganz ◽  
Song Wang ◽  
Xiao-Jun Li ◽  
Thomas Frauenheim
Keyword(s):  
Density Functional ◽  
Near Infrared ◽  
Density Functional Theory Calculations ◽  
Optical Response ◽  
Covalent Organic Frameworks ◽  
Functional Theory ◽  
Light Emitting ◽  
Light Emitting Devices ◽  
Narrow Bandgap ◽  
Potential Applications

We propose a new series of covalent–organic frameworks. These materials have narrow band gaps, leading to strong near infrared optical response. Density functional theory calculations are used to explore their properties. These novel infrared active materials may have potential applications in organic light-emitting devices, chemical and biological sensing, hybrid solar cells, or electroluminescence.

scholarly journals Strain Induced Tunability of the Electronic Properties of SrTiO3 Interfaces

2019 ◽  
Author(s):  
Zhenyun Lan ◽  
Tejs Vegge ◽  
Ivano E. Castelli
Keyword(s):  
Band Gap ◽  
Electronic Properties ◽  
Density Functional ◽  
Axial Strain ◽  
Compressive Strain ◽  
Conduction Band Edge ◽  
Biaxial Strain ◽  
Functional Theory ◽  
Structural And Electronic Properties ◽  
New Perspective

SrTiO 3 (STO) films are widely used as substrates in oxide devices. Although STO is one of the most studied materials, both experimentally and computationally, the effect of strain at the interface is almost completely ignored. In this work, we perform Density Functional Theory (DFT) calculations using the SCAN meta-GGA exchange-correlation functional to study the effect of uniaxial- and biaxial-strain on structural and electronic properties of STO interfaces. We find that under tensile uniaxial-strain, the band gap increases significantly, as a consequence of a large tilting in the octahedra. On the other side, under compression, the band gap is almost constant. Similar effects are seen for tensile biaxial strain, while for compressive strain, the gap first increases and then decreases, due to the temporary appearance of a polar distortion. In addition, we observe an orbital inversion at the conduction-band edge under different uni/bi-axial-strain conditions. This work provides a new perspective of the use of strain to modulate the structural and electronic properties of perovskite film materials for multiple applications.

scholarly journals Investigation of Opto-Electronic Properties and Stability of Mixed-Cation Mixed-Halide Perovskite Materials with Machine-Learning Implementation

Energies ◽  
2021 ◽  
Vol 14 (17) ◽  
pp. 5431
Author(s):  
Nicolae Filipoiu ◽  
Tudor Luca Mitran ◽  
Dragos Victor Anghel ◽  
Mihaela Florea ◽  
Ioana Pintilie ◽  
...  
Keyword(s):  
Machine Learning ◽  
Electronic Properties ◽  
Density Functional ◽  
Functional Theory ◽  
Regression Methods ◽  
Perovskite Materials ◽  
Mixed Cation ◽  
Visible Effect ◽  
Efficient Exploration

The feasibility of mixed-cation mixed-halogen perovskites of formula AxA’1−xPbXyX’zX”3−y−z is analyzed from the perspective of structural stability, opto-electronic properties and possible degradation mechanisms. Using density functional theory (DFT) calculations aided by machine-learning (ML) methods, the structurally stable compositions are further evaluated for the highest absorption and optimal stability. Here, the role of the halogen mixtures is demonstrated in tuning the contrasting trends of optical absorption and stability. Similarly, binary organic cation mixtures are found to significantly influence the degradation, while they have a lesser, but still visible effect on the opto-electronic properties. The combined framework of high-throughput calculations and ML techniques such as the linear regression methods, random forests and artificial neural networks offers the necessary grounds for an efficient exploration of multi-dimensional compositional spaces.

scholarly journals Strain Induced Tunability of the Electronic Properties of SrTiO3 Interfaces

2019 ◽  
Author(s):  
Zhenyun Lan ◽  
Tejs Vegge ◽  
Ivano E. Castelli
Keyword(s):  
Band Gap ◽  
Electronic Properties ◽  
Density Functional ◽  
Axial Strain ◽  
Compressive Strain ◽  
Conduction Band Edge ◽  
Biaxial Strain ◽  
Functional Theory ◽  
Structural And Electronic Properties ◽  
New Perspective

SrTiO 3 (STO) films are widely used as substrates in oxide devices. Although STO is one of the most studied materials, both experimentally and computationally, the effect of strain at the interface is almost completely ignored. In this work, we perform Density Functional Theory (DFT) calculations using the SCAN meta-GGA exchange-correlation functional to study the effect of uniaxial- and biaxial-strain on structural and electronic properties of STO interfaces. We find that under tensile uniaxial-strain, the band gap increases significantly, as a consequence of a large tilting in the octahedra. On the other side, under compression, the band gap is almost constant. Similar effects are seen for tensile biaxial strain, while for compressive strain, the gap first increases and then decreases, due to the temporary appearance of a polar distortion. In addition, we observe an orbital inversion at the conduction-band edge under different uni/bi-axial-strain conditions. This work provides a new perspective of the use of strain to modulate the structural and electronic properties of perovskite film materials for multiple applications.

The interactions between TiO2 and graphene with surface inhomogeneity determined using density functional theory

2015 ◽  
Vol 17 (44) ◽  
pp. 29734-29746 ◽  
Author(s):  
Brandon Bukowski ◽  
N. Aaron Deskins
Keyword(s):  
Density Functional Theory ◽  
Composite Materials ◽  
Electronic Properties ◽  
Density Functional ◽  
Surface Defects ◽  
Functional Theory ◽  
Surface Inhomogeneity

TiO2/graphene composites have shown promise as photocatalysts, leading to improved electronic properties. Surface defects in graphene were modeled to understand their role in these composite materials.

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