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 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.

scholarly journals Predicting the band gap of binary compounds from machine-learning regression methods

2021 ◽  
Author(s):  
Mengbo Guo ◽  
Xuyang Xu ◽  
Han Xie
Keyword(s):  
Machine Learning ◽  
Band Gap ◽  
Density Functional ◽  
Mean Squared Error ◽  
Gradient Boosting ◽  
Functional Theory ◽  
Regression Methods ◽  
Squared Error ◽  
State Band ◽  
Binary Compounds

Density functional theory (DFT) is a ubiquitous first-principles method, but the approximate nature of the exchange-correlation functional poses an inherent limitation for the accuracy of various computed properties. In this context, surrogate models based on machine learning have the potential to provide a more efficient and physically meaningful understanding of electronic properties, such as the band gap. Here, we construct a gradient boosting regression (GBR) model for prediction of the band gap of binary compounds from simple physical descriptors, using a dataset of over 4000 DFT-computed band gaps. Out of 27 features, electronegativity, periodic group, and highest occupied energy level exhibit the highest importance score, consistent with the underlying physics of the electronic structure. We obtain a model accuracy of 0.81 and root mean squared error of 0.26 eV using the top five features, achieving accuracy comparable to previously reported values but employing less number of features. Our work presents a rapid and interpretable prediction model for solid-state band gap with high fidelity to DFT and can be extended beyond binary materials considered in this study.

Unraveling The Crucial Role of Spacer Ligand in Tuning Contact Properties in Metal−2D Perovskite Interfaces

2021 ◽  
Author(s):  
Zhuo Xu ◽  
Ming Chen ◽  
Shengzhong Frank Liu
Keyword(s):  
Density Functional Theory ◽  
Electronic Properties ◽  
Crucial Role ◽  
Density Functional ◽  
State Of The Art ◽  
Schottky Barriers ◽  
Device Performance ◽  
Functional Theory

The bonding and electronic properties of electrode−2D perovskite interfaces, which play crucial role in affecting device performance, are investigated based on state-of-the-art density functional theory. Schottky barriers are observed in...

scholarly journals Role of organic cation orientation in formamidine based perovskite materials

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Siyu Liu ◽  
Jing Wang ◽  
Zhe Hu ◽  
Zhongtao Duan ◽  
Hao Zhang ◽  
...  
Keyword(s):  
Density Functional ◽  
Coupling Effect ◽  
Specific Effect ◽  
Organic Cations ◽  
Dynamic Changes ◽  
Functional Theory ◽  
Photoelectric Properties ◽  
Perovskite Materials ◽  
Work First

AbstractThe rotation of organic cations is considered to be an important reason for the dynamic changes in stability and photoelectric properties of organic perovskites. However, the specific effect of organic cations rotation on formamidine based perovskite is still unknown. In our work, first-principles calculations based on density functional theory are used to examine the effect of the rotation of formamidine cations in FAPbI3 and FA0.875Cs0.125PbI3. We have comprehensively calculated the structure, electronic and optical properties of them. We found a coupling effect between formamidine cations rotation and cesium atom. This coupling effect changes the inclination angle of octahedron to regulate electron distribution, band gaps, and optical absorption. Hence, changing the cation orientation and substitution atom is a feasible way to dynamically adjust the energy band, dielectric constant and absorption edge of perovskite. Preparing perovskite with tunable properties is just around the corner through this way.

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 Electronic Properties of Graphene-ZnO Interface: A Density Functional Theory Investigation

2019 ◽  
Author(s):  
Maryam Fathzadeh ◽  
Hamoon Fahrvandi ◽  
Ebrahim Nadimi
Keyword(s):  
Electronic Properties ◽  
Density Functional ◽  
Oxygen Vacancies ◽  
Single Layer ◽  
Binding Energies ◽  
Single Layer Graphene ◽  
Functional Theory ◽  
Interfacial Potential ◽  
Interfacial Oxygen

Our study provides significant new results for an important interface in current and future nanoelectronics, namely the Graphene-ZnO interface. The manuscript includes the results of intensive density functional calculations for the interface between several ZnO surfaces and a single layer graphene. The structural properties and the binding energies at the interface are calculated for three different ZnO surfaces. The Zn-terminated (0001) and O-terminated (000-1) surfaces as well as nonpolar (10-10) surface are considered in the present study. We also investigate the electronic properties of the contact by calculating the interfacial potential barrier based on projected density of states at different layers. The results indicate the crucial role of interfacial oxygen density on the electronic behavior of the contact, which in turn can be employed to explain experimental discrepancies on the Ohmic or Schottky behavior of this interface. Calculations for interfaces with oxygen vacancies support our finding and explain experimental results for thermally treated samples.

scholarly journals Electronic Properties of Graphene-ZnO Interface: A Density Functional Theory Investigation

2019 ◽  
Author(s):  
Maryam Fathzadeh ◽  
Hamoon Fahrvandi ◽  
Ebrahim Nadimi
Keyword(s):  
Electronic Properties ◽  
Density Functional ◽  
Oxygen Vacancies ◽  
Single Layer ◽  
Binding Energies ◽  
Single Layer Graphene ◽  
Functional Theory ◽  
Interfacial Potential ◽  
Interfacial Oxygen

Our study provides significant new results for an important interface in current and future nanoelectronics, namely the Graphene-ZnO interface. The manuscript includes the results of intensive density functional calculations for the interface between several ZnO surfaces and a single layer graphene. The structural properties and the binding energies at the interface are calculated for three different ZnO surfaces. The Zn-terminated (0001) and O-terminated (000-1) surfaces as well as nonpolar (10-10) surface are considered in the present study. We also investigate the electronic properties of the contact by calculating the interfacial potential barrier based on projected density of states at different layers. The results indicate the crucial role of interfacial oxygen density on the electronic behavior of the contact, which in turn can be employed to explain experimental discrepancies on the Ohmic or Schottky behavior of this interface. Calculations for interfaces with oxygen vacancies support our finding and explain experimental results for thermally treated samples.

The Nature of S-N Bonding in Sulfonamides and Related Compounds: Insights into π-Bonding Contributions from Sulfur K-Edge XAS

2020 ◽  
Author(s):  
Tulin Okbinoglu ◽  
Pierre Kennepohl
Keyword(s):  
Density Functional ◽  
Chemical Properties ◽  
Functional Theory ◽  
Rotational Barriers ◽  
Td Dft ◽  
Nitrogen Bonds ◽  
X Ray Absorption ◽  
Related Compounds ◽  
And Chemical Properties

Molecules containing sulfur-nitrogen bonds, like sulfonamides, have long been of interest due to their many uses and chemical properties. Understanding the factors that cause sulfonamide reactivity is important, yet their continues to be controversy regarding the relevance of S-N π bonding in describing these species. In this paper, we use sulfur K-edge x-ray absorption spectroscopy (XAS) in conjunction with density functional theory (DFT) to explore the role of S<sub>3p</sub> contributions to π-bonding in sulfonamides, sulfinamides and sulfenamides. We explore the nature of electron distribution of the sulfur atom and its nearest neighbors and extend the scope to explore the effects on rotational barriers along the sulfur-nitrogen axis. The experimental XAS data together with TD-DFT calculations confirm that sulfonamides, and the other sulfinated amides in this series, have essentially no S-N π bonding involving S<sub>3p</sub> contributions and that electron repulsion and is the dominant force that affect rotational barriers.

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