Design Of Semiconductors Research Articles

Thin film photo(electro)catalysts for the generation of energetic vectors: success cases and challenges, a brief review

Abstract Thin-film semiconductors are excellent candidates for converting solar energy into chemical energy via water splitting because of their outstanding physical and chemical properties. This review aims to provide the most recent findings on the production of energetic vectors from photo-(electro-)catalytic water splitting using thin-film semiconductors as catalysts. Recent successful cases are discussed to provide the scientific community with a guide for the design of new and advanced thin-film semiconductors with maximum efficiency for scaling the process. In addition, the use of coatings to provide a higher amount of catalyst for photo(electro)catalytic H2 production is discussed. Some of the most critical challenges in this reaction, such as charge recombination, light absorption, catalyst recovery, and stability, have been effectively addressed by applying thin films. In addition, the design of adequate thin-film photo(electro)chemical reactors is a critical step in improving efficiency and avoiding mass transfer limit steps. However, further research is required to provide continuous and low-cost manufacturing deposition techniques that favor optimal conditions to produce clean and renewable H2.

Molecular Design of n-Type Organic Semiconductors with Ultralow Electron Reorganization Energies.

Bottom-up design of n-type organic semiconductors with salient electron-transport properties is of fundamental importance. Here, with the aid of density functional theory, we demonstrate that condensing odd-membered carbon rings (5MR/7MR) to small polycyclic aromatic hydrocarbons (PAHs) can endow molecules with ultralow electron reorganization energies (λ < 100 meV). Studying 60 molecules, we find that introducing polycyclic fragments with built-in 5MR and 7MR to linear PAHs at the Cα,β positions or to nonlinear PAHs in D2h symmetry constitutes molecules with λ as low as 65 meV. A joint ACID and NICS analysis proves that the stronger the molecular aromaticity, the lower the λ will be. This is contrary to what has been previously found for p-type molecules. Furthermore, we propose "acupoints" on molecules for N-doping and cyanation, which can be used to precisely locate the substitution sites to reduce the LUMO energies (in favor of electron injection and air stability) of low-λ molecules while it does not elevate λ. These findings would help to reduce the synthetic blindness/cost and contribute to the bottom-up design of n-type small-molecule organic semiconductors.

Persistent Exciton Dressed by Weak Polaronic Effect in Rigid and Harmonic Lattice Dion-Jacobson 2D Perovskites.

The emerging two-dimensional (2D) Dion-Jacobson (DJ) perovskites with bidentate ligands have attracted significant attention due to enhanced structural stability compared with conventional Ruddlesden-Popper (RP) perovskites with monodentate ligands linked by van der Waals interactions. However, how the pure chemical bond lattice interacts with excited state excitons and its impact on the exciton nature and dynamics in 2D DJ-perovskites, particularly in comparison to RP-perovskites, remains unexplored. Herein, by a combined spectroscopy study on excitonic and structural dynamics, we reveal a persistent exciton dressed by a weak polaronic effect in DJ-perovskite due to their rigid and harmonic lattice, in striking contrast to significantly screened exciton polaron observed in RP-perovskites. Despite the similar exciton binding energy (∼0.3 eV) in both n = 1 DJ- and RP-perovskites with near-identical crystal structure, photoexcitation results in a slightly screened exciton with minimal structural relaxation and a retained binding energy of ∼0.29 eV in DJ-perovskites but strongly screened exciton polaron with a binding energy of ∼0.13 eV in RP-perovskites. Structural dynamics further highlight the rigid and harmonic lattice motion in DJ-perovskites, as opposed to the thermally activated anharmonic lattice in RP-perovskites, arising from their distinct bonding modes. Our study offers insights into modulating excited state properties in 2D perovskites, simulating the rational design of hybrid semiconductors with tailored properties and functionalities.

A-Site Doping Promotes CO2 Activation and Prolongs Charge Carrier Lifetimes in SrTiO3: Insight from Quantum Dynamics.

Using time-dependent density functional theory and nonadiabatic molecular dynamics, we systematically investigated the effect of A-site doping on the CO2 activation and charge carrier lifetimes in SrTiO3(STO). Our simulations revealed that A-site doping significantly enhances the chemical adsorption of CO2 on SrTiO3 surfaces, which is beneficial for promoting CO2 activation. Moreover, we found that A-site doping can efficiently stabilize the lowest unoccupied molecular orbital (LUMO) of CO2 near the conduction band minimum of STO, promoting the photogenerated electron transfer from the conduction band of STO to the CO2 LUMO. Importantly, A-site doping causes a significant nonadiabatic coupling reduction and prolongs the charge recombination time by a factor of 1.86 compared to the pristine STO. Our study clarifies the influencing mechanism of A-site doping on CO2 activation and charge carrier lifetimes and suggests important principles for the design of high-performance photocatalytic semiconductors.

Machine Learning-Inspired Molecular Design, Divergent Syntheses, and X-Ray Analyses of Dithienobenzothiazole-Based Semiconductors Controlled by S⋅⋅⋅N and S⋅⋅⋅S Interactions.

Inspired by the previous machine-learning study that the number of hydrogen-bonding acceptor (NHBA) is important index for the hole mobility of organic semiconductors, seven dithienobenzothiazole (DBT) derivatives 1 a-g (NHBA=5) were designed and synthesized by one-step functionalization from a common precursor. X-ray single-crystal structural analyses confirmed that the molecular arrangements of 1b (the diethyl and ethylthienyl derivative) and 1c (the di(n-propyl) and n-propylthienyl derivative) in the crystal are classified into brickwork structures with multidirectional intermolecular charge-transfer integrals, as a result of incorporation of multiple hydrogen-bond acceptors. The solution-processed top-gate bottom-contact devices of 1b and 1c had hole mobilities of 0.16 and 0.029 cm2 V-1s-1, respectively.

Carrier-Carrier Repulsion Limits the Conductivity of N-Doped Organic Semiconductors.

Molecular doping is a key strategy to enhance the electrical conductivity of organic semiconductors. Typically, the electrical conductivity shows a maximum value upon increased doping, after which the conductivity decreases. This decrease in conductivity is commonly attributed to unfavorable changes in the morphology. However, in recent simulation work, has shown, that the conductivity-at high doping-is instead limited by electron-electron repulsion rather than by morphology, at least for some material combinations. Based on the simulations, this limitation is expected to show up in the dependence of the Seebeck coefficient versus carrier density: the Seebeck coefficient will follow Heike's formula if carrier-carrier repulsion limits the conductivity. Here, the electrical conductivity and Seebeck coefficient are measured as a function of doping for a series of n-type organic semiconductors. Additionally, the resulting carrier density is measured using metal-insulator-semiconductor diodes, which link dopant loading and the number of charge carriers. At high carrier densities, the Seebeck coefficient indeed follows Heike's formula, confirming that the conductivity is limited by carrier-carrier repulsion rather than by morphological effects. This study shows that current models of hopping transport in organic semiconductors may be incomplete. As a result, this study offers novel insights in the design of organic semiconductors.

Prediction of material stability of two-dimensional semiconductors: An interpretable machine learning perspective

Despite significant advancements in leveraging artificial intelligence (AI) for drug design, materials science, and other fields, the question of how each dataset feature influences a target metric—essential for constructing better predictive models and targeted materials design—remains largely unaddressed. In this study, we explored the application of interpretable machine learning (ML) techniques to the inverse design of two-dimensional (2D) semiconductor materials, a critical yet underexplored area within the AI4Science domain. Our approach utilized a dataset from the C2DB database, incorporating advanced feature engineering and data imputation strategies to predict material stability, a key determinant of a materials industrial and academic value. Through the calculation of Shapley additive explanation scores and counterfactual analysis, we provided a nuanced understanding of feature contributions toward material stability, enabling the targeted design of 2D semiconductors with optimized properties. This work not only fills the gap in the current literature by emphasizing the role of interpretability in materials design but also demonstrates the potential of interpretable ML in guiding the development of novel materials with enhanced performance characteristics.

Systematic investigation on the rational design and optimization of bi-based metal oxide semiconductors in photocatalytic applications

To address the global energy shortage and mitigate greenhouse gas emissions on a massive scale, it is critical to explore novel and efficient photocatalysts for the utilization of renewable resources. Bi-based metal oxide (Bi x MO y ) semiconductors composed of bismuth, transition metal, and oxygen atoms have demonstrated improved photocatalytic activity and product selectivity. The vast number of element combinations available for Bi x MO y materials provides a huge compositional space for the rational design and isolation of promising photocatalysts for specific applications. In this study, we have systematically investigated the electronic and optical properties over Bi2O3 and a series of selected Bi x MO y group materials (BiVO4, BiFeO3, BiCoO3, and BiCrO3) by calculating band structure, basic optical property features, mobility and separation of charge carriers. It is clearly noted that the band gap and band edge position of the Bi x MO y group materials can be tuned in a wide range in comparison to Bi2O3. Similarly, the light response of Bi x MO y also can be broadened from the ultraviolet to the visible light region by adjusting the selection of transition metals. Additionally, the analysis of the effective mass of charge carriers of these materials further confirms their possibility in photocatalytic reaction applications because of the appropriate separation efficiency and mobility of carriers. A selection of experimental investigations on the crystal structure, composition, and optical properties of Bi2O3, BiVO4, and BiFeO3 as well as their catalytic performance in the degradation of methylene blue over was also conducted, which agree well with the theoretical predictions.

Beyond Cation Disorder: Site Symmetry‐Tuned Optoelectronic Properties of the Ternary Nitride Photoabsorber ZrTaN3

AbstractTernary nitrides are rapidly emerging as promising compounds for optoelectronic and energy conversion applications, yet comparatively little of this vast composition space has been explored. Furthermore, the crystal structures of these compounds can exhibit a significant amount of disorder, the consequences of which are not yet well understood. Here, the deposition of bixbyite‐type ZrTaN3 thin films is demonstrated by reactive magnetron co‐sputtering and observed semiconducting character, with a strong optical absorption onset at 1.8 eV and significant photoactivity, with prospective application as functional photoanodes. It is found that Wyckoff‐site occupancy of cations is a critical factor in determining these beneficial optoelectronic properties. First‐principles calculations show that cation disorder leads to minor deviations in the total energy but modulates the bandgap by 0.5 eV, changing orbital hybridization of valence and conduction band states. In addition to demonstrating that ZrTaN3 is a promising visible light‐absorbing semiconductor and active photoanode material, the findings provide important insights regarding the role of cation ordering on the electronic structure of ternary semiconductors. In particular, it is shown that not only cation order, but also the cationic Wyckoff site occupancy has a substantial impact on key optoelectronic properties, which can guide future design and synthesis of advanced semiconductors.

The impact of the nitrogen atom on the optoelectronic, nonlinear optical, and thermodynamic properties of graphene quantum dots derived from dibenzocoronene: A DFT investigation

Because of their potential applications in electricity and photonics, graphene quantum dots (GQDs) with intriguing physical characteristics have attracted a lot of attention. Here we use density functional theory (DFT) with the B3LYP functional associated with the 6–31++G(d,p) basis to explore the effect of the nitrogen atom on the optoelectronic, nonlinear optical, and thermodynamic properties of dibenzocoronene (DBC) isomers. The pristine molecules of the DBC isomers have HOMO-LUMO energy gaps of 3.39 eV (DBCa), 3.39 eV (DBCb) and 3.65 eV (DBCc). Inserting a nitrogen atom into the DBC molecular structure considerably reduces the energy gap between these two orbitals. The materials thus obtained after nitrogen doping are DBCa-N, DBCb-N, and DBCc-N and have respective gap energies of 2.05, 1.80, and 1.65 eV (in other words, less than 3 eV). It can therefore be deduced that the compounds studied will be used as semiconductors in electronics. The static polarizabilities α of the N-doped DBC isomers obtained are 442.960, 443.523, and 455.657 au, respectively, each of these values being 4 times higher than that of the organic reference molecule for non-linear optical properties (para-nitroaniline pNA α = 114.7 au), while the first-order hyperpolarizabilities β obtained are 2689.838, 5572.137, and 12717.472 au, respectively. These values are approximately 2.5, 5, and 12 times higher than those of para-nitroaniline (β = 1072.44 au). Our results confirm that the investigated DBC nitrogen derivatives are good non-linear optical materials for photonics, data storage, dynamic imaging, optical signal processing, and computer systems. All the calculated thermodynamic properties show that the proposed molecules can be easily produced. This manuscript thus stands out as a good compass in the rational design of organic semiconductors for efficient electronic devices.

Π‐Bridge Modulations in D–π–A Conjugated Microporous Polymers to Facilitate Charge Separation and Transfer Kinetics for Efficient Photocatalysis

AbstractThe burgeoning field of conjugated microporous polymers (CMPs) has generated widespread interest due to their potential as photocatalysts for hydrogen production from water. Nevertheless, their photocatalytic performance is sometimes hindered by inadequate charge separation and transfer, coupled with rapid charge recombination. Herein, a strategy to enhance photocatalytic performance via the customization of π‐bridges through the modulation of heteroatoms in a series of donor‐π‐acceptor (D‐π‐A) CMPs is proposed. This affords optimized energy levels and improved charge separation and transfer, thus boosting photocatalytic efficiency. Among various heteroatom substitutions, S‐doped CMP (10 mg) demonstrates the highest photocatalytic hydrogen evolution rate of 203 µmol h−1 (AQY450nm = 7.4%) under visible light irradiation. Subsequent experimental analysis reveals its superior photocatalytic performance can be largely related to its minimized exciton binding energy, facilitated charge transfer efficiency, and impeded charge recombination among these heteroatom‐doped D‐π‐A CMPs. This research paves the way for the rational design and modification of organic semiconductors for advanced solar‐driven photocatalysis by promoting charge separation and transfer.

Electronic and Structural Properties of Antibacterial Ag–Ti-Based Surfaces: An Ab Initio Theoretical Study

Coatings with tunable multifunctional features are important for several technological applications. Ti-based materials have been used in diverse applications ranging from metallic diodes in electronic devices up to medical implants. This work uses ab initio calculations to achieve a more fundamental understanding of the structural and electronic properties of β-TiNb and its passive TiO2 film surfaces upon Ag addition, investigating the alterations in the electronic band gap and the stability of the antibacterial coating. We find that Ag’s 4d electrons introduce localized electron states, characterized by bonding features with the favoured Ti first neighbour atoms, approximately −5 eV below the fermi level in both β-TiNb bulk and surface. Ag’s binding energy on β-TiNb(110) depends on the local environment (the lattice site and the type of bonded surface atoms) ranging from −2.70 eV up to −4.21 eV for the adatom on a four-fold Ti site, offering a variety of options for the design of a stable coating or for Ag ion release. In Ti–O terminated anatase and rutile (001) surfaces, surface states are introduced altering the TiO2 band gap. Silver is bonded more strongly, and therefore creates a more stable antibacterial coat on rutile than on anatase. In addition, the Ag coating exhibits enhanced 4d electron states at the highest occupied state on anatase (001),which are extended from −5 eV up to the Fermi level on rutile (001), which might be altered depending on the coat structural features, thus creating systems with tunable electronic band gap that can be used for the design of thin film semiconductors.

Is Dielectric Mismatch Actually Important in 2D Perovskites?

Understanding and controlling exciton properties are important for the design of 2D semiconductors, such as monolayer transition metal dichalcogenides (TMDCs) and 2D halide perovskites (HPs). This paper demonstrates that the widespread strategy used for the exciton engineering of 2D HPs, based on dielectric mismatch, is flawed since dielectric mismatch has very little correlation with exciton properties. For monolayer TMDCs, however, the dielectric mismatch is shown to be more important.

Vinyl-Group-Anchored Covalent Organic Framework for Promoting the Photocatalytic Generation of Hydrogen Peroxide.

The artificial photosynthesis of H2O2 from water and oxygen using semiconductor photocatalysts is attracting increasing levels of attention owing to its green, environmentally friendly, and energy-saving characteristics. Although covalent organic frameworks (COFs) are promising materials for promoting photocatalytic H2O2 production owing to their structural and functional diversity, they typically suffer from low charge-generation and -transfer efficiencies as well as rapid charge recombination, which restricts their use as catalysts for photocatalytic H2O2 production. Herein, we report a strategy for anchoring vinyl moieties to a COF skeleton to facilitate charge separation and migration, thereby promoting photocatalytic H2O2 generation. This vinyl-group-bearing COF photocatalyst exhibits a H2O2-production rate of 84.5 μmol h-1 (per 10 mg), which is ten-times higher than that of the analog devoid of vinyl functionality and superior to most reported COF photocatalysts. Both experimental and theoretical studies provide deep insight into the origin of the improved photocatalytic performance. These findings are expected to facilitate the rational design and modification of organic semiconductors for use in photocatalytic applications.

Vinyl‐Group‐Anchored Covalent Organic Framework for Promoting the Photocatalytic Generation of Hydrogen Peroxide

AbstractThe artificial photosynthesis of H2O2 from water and oxygen using semiconductor photocatalysts is attracting increasing levels of attention owing to its green, environmentally friendly, and energy‐saving characteristics. Although covalent organic frameworks (COFs) are promising materials for promoting photocatalytic H2O2 production owing to their structural and functional diversity, they typically suffer from low charge‐generation and ‐transfer efficiencies as well as rapid charge recombination, which restricts their use as catalysts for photocatalytic H2O2 production. Herein, we report a strategy for anchoring vinyl moieties to a COF skeleton to facilitate charge separation and migration, thereby promoting photocatalytic H2O2 generation. This vinyl‐group‐bearing COF photocatalyst exhibits a H2O2‐production rate of 84.5 μmol h−1 (per 10 mg), which is ten‐times higher than that of the analog devoid of vinyl functionality and superior to most reported COF photocatalysts. Both experimental and theoretical studies provide deep insight into the origin of the improved photocatalytic performance. These findings are expected to facilitate the rational design and modification of organic semiconductors for use in photocatalytic applications.

High Open-Circuit Voltage Organic Solar Cells with 19.2% Efficiency Enabled by Synergistic Side-Chain Engineering.

Restricted by the energy-gap law, state-of-the-art organic solar cells (OSCs) exhibit relatively low open-circuit voltage (VOC) because of large nonradiative energy losses (ΔEnonrad). Moreover, the trade-off between VOC and external quantum efficiency (EQE) of OSCs is more distinctive; the power conversion efficiencies (PCEs) of OSCs are still <15% with VOCs of >1.0V. Herein, the electronic properties and aggregation behaviors of non-fullerene acceptors (NFAs) are carefully considered and then a new NFA (Z19) is delicately designed by simultaneously introducing alkoxy and phenyl-substituted alkyl chains to the conjugated backbone. Z19 exhibits a hypochromatic-shifted absorption spectrum, high-lying lowest unoccupied molecular orbital energy level and ordered 2D packing mode. The D18:Z19-based blend film exhibits favorable phase separation with face-on dominated molecular orientation, facilitating charge transport properties. Consequently, D18:Z19 binary devices afford an exciting PCE of 19.2% with a high VOC of 1.002V, surpassing Y6-2O-based devices. The former is the highest PCE reported to date for OSCs with VOCs of >1.0V. Moreover, theΔEnonrad of Z19- (0.200eV) and Y6-2O-based (0.155eV) devices are lower than that of Y6-based (0.239eV) devices. Indications are that the design of such NFA, considering the energy-gap law, could promote a new breakthrough in OSCs.

What's behind their various activities? Discerning the importance of surface terminations in Ag3PO4 semiconductor from DFT calculations

The surface energy and band gap of inorganic semiconductors are essential properties for a wide variety of applications in materials science, and studying morphologies holds significant importance. However, it is challenging to find a correlation between them at the atomic scale when these materials are multifunctional. This motivates the development of predictive computational models that can optimize these materials based on these quantities. Present findings shed light on the structure and electronic properties of (100), (110), and (111) surfaces of Ag3PO4 by using density functional theory calculations. By introducing two concepts, namely, polyhedron energy and polyhedron band gap, we provide compelling evidence for the effects of surface termination of Ag3PO4 photocatalyst. We compare our predictions to experimental crystal habits, and our results not only allow us to explain their evolution for obtaining a given morphology but also offer a coherent explanation, based on atomic-scale insights, for the discrepancies of morphology-photocatalytic activity relationship of Ag3PO4 in the recent literature. Overall, this work opens a novel avenue for first-principles calculations of morphology and provides a roadmap for the design of more effective inorganic semiconductors with desirable physicochemical properties for potential applications.

Methods and applications of machine learning in computational design of optoelectronic semiconductors

Methods and applications of machine learning in computational design of optoelectronic semiconductors

Customizing Wettability of Defect-Rich CeO2/TiO2 Nanotube Arrays for Humidity-Resistant, Ultrafast, and Sensitive Ammonia Response.

In all their applications, gas sensors should satisfy several requirements, including low cost, reduced energy consumption, fast response/recovery, high sensitivity, and reliability in a broad humidity range. Unfortunately, the fast response/recovery and sensing reliability under high humidity conditions are often still missing, especially those working at room temperature. In this study, a humidity-resistant gas sensor with an ultrafast response/recovery rate was designed by integrating a defect-rich semiconducting sensing interface and a self-assembled monolayer (SAM) with controllable wettability. As a proof-of-concept application, ammonia (NH3), one of the atmospheric and indoor pollutants, was selected as the target gas. The decoration of interconnected defective CeO2 nanowires on spaced TiO2 nanotube arrays (NTAs) provided superior NH3 sensing performances. Moreover, we showed that manipulating the functional end group of SAMs is an efficient and simple method to adjust the wettability, by which 86% sensitivity retention with an ultrafast response (within 5 s) and a low limit of detection (45 ppb) were achieved even at 75% relative humidity and room temperature. This work provides a new route toward the comprehensive design and application of metal oxide semiconductors for trace gas monitoring under harsh conditions, such as those of agricultural, environmental, and industrial fields.

Direct Band Gap Semiconductors with Two- and Three-Dimensional Triel-Phosphide Frameworks (Triel=Al, Ga, In).

Recently, several ternary phosphidotrielates and -tetrelates have been investigated with respect to their very good ionic conductivity, while less focus was pointed towards their electronic structures. Here, we report on a novel series of compounds, in which several members possess direct band gaps. We investigated the known compounds Li3AlP2, Li3GaP2, Li3InP2, and Na3InP2 and describe the synthesis and the crystal structure of novel Na3In2P3. For all mentioned phosphidotrielates reflectance UV-Vis measurements reveal direct band gaps in the visible light region with decreasing band gaps in the series: Li3AlP2 (2.45 eV), Li3GaP2 (2.18 eV), Li3InP2 (1.99 eV), Na3InP2 (1.37 eV), and Na3In2P3 (1.27 eV). All direct band gaps are confirmed by quantum chemical calculations. The unexpected property occurs despite different structure types. As a common feature all compounds contain EP4 tetrahedra, which share exclusively vertices for E=In and vertices as well as edges for E=Al and Ga. The structure of the novel Na3In2P3 is built up by a polyanionic framework of six-membered rings of corner-sharing InP4 tetrahedra. As a result, the newly designed semiconductors with direct band gaps are suitable for optoelectronic applications, and they can provide significant guidance for the design of new functional semiconductors.