Conduction Band Of Semiconductor Research Articles

Influence of Mixing Valence Band States to the Conduction Band States on Two-Quantum Linear-Circular Dicroism in Semiconductors

A quantitative theory of two-photon linear-circular dichroism caused between the subbands of light and heavy holes of the valence band and conduction band is constructed, which takes into account the admixture of valence band states to the conduction band states and the temperature dependence of the band gap (Eg(T)) in semiconductors of tetrahedral symmetry in the multiband Kane model. It is shown that the type of oscillatory angular dependence or the amplitude values of the probabilities of two-photon optical transitions depend on the state of light polarization. This is due to the fact that, under the influence of linearly polarized light, alignment along the pulse occurs, and under the action of circularly polarized light, the moments of current carriers are oriented. It has been determined that the probability of two-photon optical transitions from the heavy hole subband to the conduction band of semiconductors at a fixed temperature increases with increasing frequency, passes through a maximum, and sharply decreases regardless of the degree of polarization of light, as well as the band gap.

(Invited) Fundamentals of Plasmon-Induced Charge Transfer in Semiconducting Materials: Showcasing OER Catalysis

Using Localized Surface Plasmon Resonance Effect for Enhancing Electrochemical reactions has been reported earlier both in terms of direct electron injection/transfer (DET) in outer-sphere reductive processes as well as charge injection into semiconductors via plasmon-induced resonant electron transfer processes (PIRE). While the former (DET) is mainly influenced by the lifetimes of the ejected hot electrons and their rapid cooling at the interface. For inner sphere reductive processes via the LSPR phenomenon, direct charge injection into the LUMO states of the adsorbed species is required. In this regard, it is imperative to distinguish between the inter-band charge transfer of the adsorbed species because of exposure to photons.In contrast to these charge injections into semiconductors via plasmon-induced resonant electron transfer processes (PIRE), they must be more understood and complex. In this presentation, we will use the well-known endothermic anodic oxygen evolution reaction (OER) in alkaline pH to showcase the fundamental aspects of charge injection and its effect on the hole-driven OER mechanism. For this well-known OER catalyst, layered double hydroxides of Ni with Fe and Co dopants will be used. The electrochemical enhancement of OER will be explained based on detailed structural motifs of the semiconductors, its band structure, and the resonance effect of Au induced by the LSPR effect. Direct and indirect bandgaps will be discussed in the context of three possible mechanisms: (i) Charge carriers are directly injected into the semiconductor via LSPR. The semiconductor's conduction band is usually (-0.1 to 0.0 eV vs. NHE), and the valence band is between (2.00 and 3.5 eV), corresponding to electron energy between -2.00 to 3.5 eV vs. NHE. For LSPR nanoparticles, SPR energy is between 1.0 and 4.0 eV. Also, the Fermi energy of LSPR is usually 0.0 vs. NHE. Hence, LSPR only enables energetic electrons to be transferred from metals to semiconductors. It is the interface between LSPR and the semiconductor which is important. Charge injection is more prevalent when metal LSPR is of lower energy than the semiconductor—direct electron transfer (DET). (ii) Transfer does not involve direct electron injection but via (a) near-field electromagnetic and (b) resonant photon scattering mechanism. This has been shown to work by adding a thin dielectric material between the LSPR and the semiconductor. This would be most likely in the case of OER, where surface-localized plasmons will be the most important determinant instead of recombination events in the bulk of the semiconductor. This is most important for OER as it depends on the surface hole concentration. It should be noted that larger nanoparticles (>50 nm) have increased resonant photon scattering. Such a mechanism is more prevalent when we overlap metal LSPR and semiconductor bands, leading to plasmon-induced resonant electron transfer (PIRET). (iii) When metal LSPR is in direct contact with the semiconductor, all three phenomena could be active.

Unveiling the potential of TPA-based molecules to tune the optoelectronic properties and enhance the efficiency of dye-sensitized solar cells.

The world's energy and environmental requirements are changing due to rapid population growth and industrial growth, and solar cells can be used to meet these demands. Dye-sensitized solar cells (DSSCs) are solar cells in which energy conversion occurs via a process similar to photosynthesis in plants. DSSC development is still in its infancy. DSSCs can operate under cloudy conditions and indirect sunlight and have attracted considerable attention due to their low cost and high efficiency. We designed two metal-free TPA-based dyes (Dye2 and Dye3) based on the reference dye Mg207 (Dye1) by increasing the donor strength of the molecule, as such dyes have shown enhanced efficiency in DSSCs. Moreover, the triphenylamine (TPA) moiety has been demonstrated to be a good donor that prevents charge recombination. Intramolecular charge transfer (ICT) from the donor to acceptor moiety was found in the sensitizers, and electrons were promoted to the conduction band (CB) of the TiO2 semiconductor. The negative binding energy of the dye@TiO2 clusters indicated that dye adsorption on the semiconductor surface was stable. The double donor increased the electron injection and electronic coupling constants in Dye2 and Dye3, indicating that these newly designed dyes have superior charge injection capacity. Accordingly, the efficiencies of DSSCs with Dye2 and Dye3 were 9.77% and 9.62%, respectively, and substitution with the TPA unit at the -R1 and -R2 positions in Dye1 resulted in better power conversion compared to the parent compound (9.09%). Increased donor strength improved photovoltaic performance by increasing current density and light-harvesting efficiency. This is a good molecular design approach for preparing targeted donor- -acceptor (D- -A) organic dyes with high DSSC efficiency. To predict the charge transport and optoelectronic characteristics of the TPA dyes, quantum chemical calculations were carried out using Gaussian16. The ground-state (S0) optimized geometries of the sensitizers were computed by utilizing DFT at the B3LYP/6-31G** level. The absorption spectra ( max) were computed by employing TD-DFT with various functionals (B3LYP, PBE1PBE, CAM-B3LYP, and BHandHLYP) in the gas and solvent (DCM) phases. Among the studied functionals, BHandHLYP was found to be best at successfully reproducing the experimental data. Thus, the absorption spectra of the newly designed dyes and dye@TiO2 were calculated at the BHandHLYP/6-31G** level. The dye@TiO2 cluster optimizations were carried out at the B3LYP/6-31G**(LANL2DZ) level.

Study of rutile TiO2(110) single crystal by transient absorption spectroscopy in the presence of Ce4+ cations in aqueous environment. Implication on water splitting

Ce4+ cations are commonly used as electron acceptors during the water oxidation to O2 reaction over Ir- and Ru-based catalysts. They can also be reduced to Ce3+ cations by excited electrons from the conduction band of an oxide semiconductor with a suitable energy level. In this work, we have studied their interaction with a rutile TiO2(110) single crystal upon band gap excitation by femtosecond transient absorption spectroscopy (TAS) in solution in the 350–900 nm range and up to 3.5 ns. Unlike excitation in the presence of water alone the addition of Ce4+ resulted in a clear ground-state bleaching (GSB) signal at the band gap energy of TiO2 (ca. 400 nm) with a time constant t = 4–5 ps. This indicated that the Ce4+ cations presence has quenched the e-h recombination rate when compared to water alone. In addition to GSB, two positive signals are observed and are attributed to trapped holes (in the visible region, 450–550 nm) and trapped electrons in the IR region (>700 nm). Contrary to expectation, the lifetime of the positive signal between 450 and 550 nm decreased with increasing concentrations of Ce4+. We attribute the decrease in the lifetime of this signal to electrostatic repulsion between Ce4+ at the surface of TiO2(110) and positively charged trapped holes. It was also found that at the very short time scale (<2–3 ps) the fast decaying TAS signal of excited electrons in the conduction band is suppressed because of the presence of Ce4+ cations. Results point out that the presence of Ce4+ cations increases the residence time (mobility) of excited electrons and holes at the conduction band and valence band energy levels (instead of being trapped). This might provide further explanations for the enhanced reaction rate of water oxidation to O2 in the presence of Ce4+ cations.

To the theory of dimensional quantization in crystals in the Kane approximation

The microscopic mechanism of size quantization of the conduction band and valence band of semiconductors of cubic and tetrahedral symmetry has been theoretically studied in the Kane approximation. It is shown that the matrix Schrödinger equation obtained on the basis of the Kane model cannot be solved analytically for a potential well of an arbitrary profile. Therefore, expressions for the energy spectrum are obtained depending on the two-dimensional wave vector directed along the interface of the heterostructure for various cases that differ in the range of current carrier energy values.

Engineering highly efficient porphyrin sensitizers through metal, ligand and bridge modification: a DFT study.

This work presents a systematic investigation of porphyrin sensitizers for application in dye-sensitized solar cells (DSSCs). Density functional theory calculations, including both static and time-dependent methods, were employed to evaluate a series of candidate dyes for their potential to achieve high power conversion efficiency. The well-established SM315 dye, known for its record-breaking PCE of 13%, was adopted as a reference point. A range of metal atoms including alkaline-earth and 3d transition metals were screened, Ca was identified as the most promising metal for light capture and conversion. Ca-porphyrin-based sensitizer was further modified by introducing different axial ligands and four distinct bridging units. The designed dyes exhibit red-shifted absorption spectra and optimal frontier orbital alignment with the semiconductor's conduction band, promoting efficient light capture and charge transfer. In addition to these core parameters, a comprehensive analysis of light harvesting efficiency (LHE), reorganization energy (λ), short-circuit current density (JSC), exciton binding energy (EBE), open-circuit voltage (VOC), electron transfer rate (k), polarization (α) and hyperpolarization (βtot) collectively paint a clear picture of superior light capture, efficient charge transport dynamics, and minimized energy losses within the designed dyes. This ultimately translates to the remarkable power conversion efficiency (PCE) exceeding 27% achieved by the specifically designed dye with the Ca as metal atom, 4,4'-bipyridine as axial ligands and cyclopenta-1,3-diene as bridging unit, surpassing the performance of SM315 dye (13% PCE). This systematic study combines the design of high-performance porphyrin sensitizers through molecular engineering with a comprehensive investigation of their impact on DSSC function using advanced computational methods.

Bifunctional phosphate-modulated Cu2O/CeO2 redox heterojunction: A promising approach for proficient CO2 reduction

The construction of extremely dispersed redox-heterojunctions is a critical step toward improving of photocatalytic activity. Nonetheless, electron transfer faces momentous hurdles at the interfaces of these redox-heterojunction, mainly as a result of the considerable gap and potential-barrier between them. To address this obstacle, a bifunctional phosphate was deliberately introduced as an electron-bridge into the Cu2O/CeO2 redox-heterojunction system, aiming to necessitate a potential-barrier, establish a photoelectron transport route to improve the surface catalysis, and serve as a catalyst stabilizer, leading to improved dispersion of Cu2O on the CeO2 surface. The resultant intricately dispersed and optimized redox-heterojunction showcased an unparalleled advancement in apparent quantum efficiency (AQE), attaining an approximate value of 1.41 % at 420 nm during the photocatalytic CO2 reduction. The experimental findings established a conspicuous association between the substantial increase in AQE and the diminished interfacial migration resistance, heightened dispersion, and abundance of more active-sites, all accredited to phosphate-modulation in the redox-heterojunction. The work emphasizes the significant importance of phosphate in bridging the conduction and valence bands of semiconductors, leading to enhanced photocarrier separation efficiency and improved molecular dispersion.

A Theoretical Study of The Influence of Donor Sensitize Dye on Performance of Dye-sensitized Solar Sells DSSCs

In this paper, a theoretical study was introduced to discussion the Influence of donor senstizer on efficiency of solar cell with clear focusing on dye senstized solar cell DSSCs applications was presented. Use of donor as -sensitizer dye in solar cells was a viable contender in photovoltaics due to their spectrum of excited state to transfer more elkectrons to conduction band of semiconductor .In this study, two systems Alq3/ZnO and D149/ZnO devices taken with same two solvents .Transtion energy ,coupling strength and transtion parameters are used to calculate the electron current density , it uses to calculate the photovoltic characteristic I-V ,fill factor and the efficiency of the solar cell. Especially, the largest performance was for the both D149/ ZnO and Alq3/ZnO solar cells based on Acetonitrile as a solvent with electron current density of (430 0.329-13.8) mA/cm^2 between (1-6) V and produced the highest efficiency calculated 2.593 and 0.938for the both solar cell was corresponds to the lowest efficiency about 0.536 for Alq3/ZnO with Ethanol solvent

Designing Efficient Metal-Free Dye-Sensitized Solar Cells: A Detailed Computational Study.

The modulation of molecular characteristics in metal-free organic dyes holds significant importance in dye-sensitized solar cells (DSSCs). The D-π-A molecular design, based on the furan moiety (π) in the conjugated spacer between the arylamine (D) and the 2-cyanoacrylic acid (A), was developed and theoretically evaluated for its potential application in DSSCs. Utilizing linear response time-dependent density functional theory (TDDFT) with the CAM-B3LYP functional, different donor and acceptor groups were characterized in terms of the electronic absorption properties of these dyes. All the studied dye sensitizers demonstrate the ability to inject electrons into the semiconductor's conduction band (TiO2) and undergo regeneration through the redox potential triiodide/iodide (I3-/I-) electrode. TDDFT results indicate that the dyes with CSSH anchoring groups exhibit improved optoelectronic properties compared to other dyes. Further, the photophysical properties of all dyes absorbed on a Ti(OH)4 model were explored and reported. The observed results indicate that bidentate chemisorption occurs between dyes and TiO4H5. Furthermore, the HOMO-LUMO energy gaps for almost all dye complexes are significantly smaller than those of the free dyes. This decrease of the HOMO-LUMO energy gaps in the dye complexes facilitates electron excitation, and thus more photons can be adsorbed, guaranteeing larger values of efficiency and short-circuit current density.

Significance of anchoring group design on light harvesting efficiency of dye-sensitized solar cells and non-linear optical response

Dye-sensitizers designed from coumarin backbone are widely utilized in solar light harvesting due to their versatile performance in dye-sensitized solar cells (DSSC). They are well-known as non-linear optical (NLO) materials. In this case study, we have designed coumarin-based sensitizers containing thiophene as a common spacer with the different acceptor-anchoring groups, ethyl-2-cyanoacrylate (SPDSSC 1) and 2-cyanoacrylic acid (SPDSSC 2). Density functional theory (DFT) and time-dependent- DFT (TD-DFT) computational calculations of these molecules predict superior light harvesting capability and NLO properties. The calculated HOMO–LUMO energy gap of these dyes showed an inverse relation with chemical potential and electrophilicity index and was directly related to hardness and hyperhardness. It was also seen β0 and γ and PCE follow a similar trend. Further, computations of sensitizers@TiO2 indicated sensitizers with ethyl-2-cyanoacrylate bonded with TiO2 cluster via unidentate linkage, whereas 2-cyanoacrylic acid containing sensitizer involved bidentate bonding with TiO2. Apart from this, sensitizers with 2-cyanoacrylic acid anchors showed much planer geometry. Also, the quantitative analysis of the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) and MEP plots showed that more electron clouds shifted to the TiO2 cluster in the sensitizer with 2-cyanoacrylic acid (SPDSSC 2) than ethyl-2-cyanoacrylate (SPDSSC 1). Further, both molecules were taken as sensitizers in the DSSC device. SPDSSC 2 showed higher power conversion efficiency than SPDSSC 1. Overall, results disclosed that sensitizers with ethyl-2-cyanoacrylate having two oxygen atoms in their anchoring part could bind with only carbonyl oxygen. And this monodentate binding of ethyl-2-cyanoacrylate with TiO2 leads to poor charge transfer in the semiconductor's conduction band, resulting in poor DSSC performance.

Quantum recurrence times in nanostructures

We compute the classical and revival times of electron currents in several bulk nanostructured, semiconductor materials. We have used a nonparabolic Schrödinger equation to model the conduction band of semiconductors. We have calculated the classical and revival periods for quantum dots of Si, Ge and InAs quantum dots. The obtained results are of the order of tenths of nanoseconds to picoseconds, which are within reach of current technologies.

Multi-step photon upconversion in quantum-dot-based solar cells with a double-heterointerface structure

Photon upconversion (PU) is a process where an electron is excited from the valence band to the conduction band of a wide-gap semiconductor by the sequential absorption of two or more photons via real states. For example, two-step PU can generate additional photocurrent in the so-called intermediate-band solar cells. In this work, we consider two- and three-step processes; we study multi-step PU in a quantum dot (QD)-based single-junction solar cell with a double-heterointerface structure. The solar cell consists of three different absorber layers: Al0.7Ga0.3As, Al0.3Ga0.7As, and GaAs, which form two heterointerfaces. Just beneath each heterointerface, an InAs/GaAs QD layer was inserted. After band-to-band excitation, electrons accumulate at each heterointerface, and then, below-bandgap photons excite a certain fraction of these electrons above the barrier energy. The photoluminescence spectra of the InAs QDs reveal slightly different QD size distributions at the two heterointerfaces. We show that the external quantum efficiency is improved by additional irradiation with below-bandgap infrared photons, which suggests a multi-step PU process that involves the two heterointerfaces. The dependence of the photocurrent on the infrared excitation power density only shows a superlinear behavior when the GaAs layer is excited but the Al0.3Ga0.7As layer is not. These data demonstrate a multi-step PU process that consists of one intraband transition at each of the two heterointerfaces and one interband transition in GaAs.

Synergistic Effect of Pd Co-Catalyst and rGO–TiO2 Hybrid Support for Enhanced Photoreforming of Oxygenates

Photoreforming biomass-derived waste such as glycerol into hydrogen fuel is a renewable hydrogen generation technology that has the potential to become important due to unavoidable CO2 production during methane steam reforming. Despite tremendous efforts, the challenge of developing highly active photocatalysts at a low cost still remains elusive. Here, we developed a novel photocatalyst with a hybrid support comprising reduced graphene oxide (rGO) and TiO2 nanorods (TNR). rGO in the hybrid support not only performed as an excellent scavenger of electrons from the semiconductor conduction band due to its suitable electrochemical potential, but also acted as an electron transport highway to the metal co-catalyst, which otherwise is not possible by simply increasing metal loading due to the shadowing effect. A series of hybrid supports with different TNR and rGO ratios were prepared by the deposition method. Pd nanoparticles were deposited over hybrid support through the chemical reduction method. Pd/rGO-TNRs photocatalyst containing 4 wt.% rGO contents in the support and 1 wt.% nominal Pd loading demonstrated hydrogen production activity ~41 mmols h−1g−1, which is 4 and 40 times greater than benchmark Au/TiO2 and pristine P25. The findings of this works provide a new strategy in optimizing charge extraction from TiO2, which otherwise has remained impossible due to a fixed tradeoff between metal loading and the detrimental shadowing effect.

Optimization, fabrication, and characterization of anthocyanin and carotenoid derivatives based dye-sensitized solar cells

The bracts of Poinsettia, Tamarillo fruit, Annatto seeds, and Pungent Chillies have been used to extract the dyes using ethanol and deionized water. A cocktail of the dyes has been made with equal concentration and will be used as a sensitizer in the proposed dye-sensitized solar cell. The individual and cocktail of the dyes are subjected to FTIR, UV–Visible spectroscopy for the identification of functional groups, and absorption wavelength to find the effectiveness of the dyes for absorption of energy of the photons. From the study, it is found that the sensitizers in the dyes have shown stronger electronic coupling and rapid electron transfer into the conduction band of the TiO2 semiconductor on the FTO substrate. J-V analysis represents photovoltaic characterization of assembled thin film nano-crystalline solar cells. Anthocyanin derivative of Poinsettia bracts attained a photo-sensitized conversion efficiency of 1.74% achieving an overlong lifespan of electrons. Ethanol was chosen for attaining the best energy conversion efficiency owing to its polarity. The presence of phytoconstituents has an impact on the color of the sensitizers and the degradation in the power conversion efficiencies was also monitored. This research examines the parameters that influence the stability of anthocyanin and carotenoid pigments, as well as the solvents required for effective derivative extraction.

Band alignment study at the SrTaO2N / H2O interface varying lattice constants and surface termination from first-principles calculations

In the search for new renewable energy to replace fossil fuels, Hydrogen is one of the most promising candidates for clean energy production. But cheap Hydrogen separation and storage is still a big challenge. Photoelectrochemical devices look promising for the decomposition of the water molecule into 2H2 + O2. Every day new materials and combinations are discovered or invented to improve the efficiency of the complex total process. A necessary condition for the photoelectrochemical process to work without a bias voltage is that the minimum of the semiconductor conduction band must be more positive than the reduction potential H+ to H2, whereas the maximum of the semiconductor valence band must be more negative than the oxidation potential of H2O to O2. Thus, band alignment studies in interfaces of semiconductors with water become of vital importance.In this work, first-principles calculations based on density–functional theory (DFT) in the all-electron and the pseudo-potential approaches have been performed for the analysis of the band alignment in SrTaO2N/H2O interfaces. Different surface orientations were analyzed, together with the dependence of the gap and band alignment with lattice constants for systems grown on mismatched substrates. Water structures were built from classical molecular dynamics and its electronic structure calculated using DFT. The calculations show that the SrTaO2N (001) is suitable for photoelectrochemical applications on a wide range of lattice constant a, except for a compression/elongation of −2%, −1% and 3%, while SrTaO2N (110) results suitable for photoelectrochemical devices over a wider range of lattice constants from −1% to 3%.

Photothermal Catalytic Reduction of CO2 by Cobalt Silicate Heterojunction Constructed from Clay Minerals

The coupled utilization of solar and thermal energy is considered an efficient way to improve the efficiency of CO2 reduction. Herein, palygorskite (Pal) clay is as a silicon source, while Co2+ is introduced to prepare two-dimensional Co2SiO4 nanosheets, and the excess of Co2+ leads to the growth of Co3O4 on the surface of Co2SiO4 to obtain an S-scheme Co2SiO4/Co3O4−x heterojunction, which facilitates the charge transfer and maintains higher redox potentials. Benefiting from black color and a narrow band gap, the cobalt oxide on the surface can increase the light absorption and produce a local photothermal effect. Under proper thermal activation conditions, the photoelectrons captured by the abundant oxygen vacancies can obtain a secondary leap to the semiconductor conduction band (CB), suppressing the recombination of electron-hole pairs, thus favoring the electron transfer on Co2SiO4/Co3O4−x. The composites not only have abundant oxygen vacancies, but also have a large specific surface area for the adsorption and activation of CO2. The yields of CH3OH on Co2SiO4/Co3O4−5% reach as high as 48.9 μmol·g−1·h−1 under simulated sunlight irradiation. In situ DRIFTS is used to explore the photocatalytic reduction CO2 mechanism. It is found that the thermal effect facilitates the generation of the key intermediate COOH* species. This work provides a new strategy for photothermal catalytic CO2 reduction by taking advantage of natural clay and solar energy.

Prediction of bipolar VSi2As4 and VGe2As4 monolayers with high Curie temperature and strong magnetocrystalline anisotropy

Recent studies have demonstrated that two-dimensional intrinsic magnetic materials with high Curie temperature $({T}_{\text{c}})$ and large magnetic anisotropy energy (MAE) are highly desirable for future spintronics. After careful investigations through density functional theory, bipolar ${\mathrm{VSi}}_{2}{\mathrm{As}}_{4}$ and ${\mathrm{VGe}}_{2}{\mathrm{As}}_{4}$ monolayers, with semiconductor valence and conduction band edges fully spin polarized in different spin directions, are demonstrated to be highly stable and have in-plane ferromagnetism (FM) with large MAE of $\ensuremath{\sim}5.5$ meV. The FM interaction is found to be dominated by the superexchange between d orbitals of V atoms through p orbitals of anions. More interestingly, ${T}_{\text{c}}$ is estimated to be $\ensuremath{\sim}900$ K through Monte Carlo simulation, which is significantly higher than room temperature. In addition, both MAE and ${T}_{\text{c}}$ can be substantially regulated and increased under biaxial strain and the transition from FM semiconductors to metals will occur. Our calculations and analyses indicate that ${\mathrm{VSi}}_{2}{\mathrm{As}}_{4}$ and ${\mathrm{VGe}}_{2}{\mathrm{As}}_{4}$ monolayers are ideal systems for the fundamental understanding of magnetic physics as well as building blocks for magnetoelastic applications, high-temperature, or/and gate-tunable spintronic nanodevices.

Synthesis and applications of TiO2/ZnO hybrid nanostructures by ZnO deposition on TiO2 nanotubes using electrochemical processes

Abstract In recent years, TiO2/ZnO hybrid nanostructures have been attracting the interest of the scientific community due to their excellent photoelectrochemical properties. The main advantage of TiO2/ZnO hybrid nanostructures over other photocatalysts based on semiconductor materials lies in their ability to form heterojunctions in which the valence and conduction bands of both semiconductors are intercalated. This factor produces a decrease in the band gap and the recombination rate and an increase in the light absorption range. The aim of this review is to perform a revision of the main methods to synthesise TiO2/ZnO hybrid nanostructures by ZnO deposition on TiO2 nanotubes using electrochemical processes. Electrochemical synthesis methods provide an easy, fast, and highly efficient route to carry out the synthesis of nanostructures such as nanowires, nanorods, nanotubes, etc. They allow us to control the stoichiometry, thickness and structure mainly by controlling the voltage, time, temperature, composition of the electrolyte, and concentration of monomers. In addition, a study of the most promising applications for TiO2/ZnO hybrid nanostructures has been carried out. In this review, the applications of dye-sensitised solar cell, photoelectrocatalytic degradation of organic compounds, photoelectrochemical water splitting, gas sensors, and lithium-ion batteries have been highlighted.

Designing of PC31BM‐based acceptors for dye‐sensitized solar cell

AbstractThree push‐pull dyes with triphenylamine as donor, thiophene as spacer and fullerene‐based acceptors have been designed using density functional theory (DFT) for dye‐sensitized solar cells (DSSCs). Here, we have done a systematic case study by varying the acceptor of dye. PCBM type of acceptors are chosen. However, the main focus lies on the fact that fullerene C60, which is used as conventional fullerene in PCBM, is replaced by C30. Further, two more structures are derived, where C30 is changed by two of its doped counterparts, C10B10N10 and C10B10P10. Structural integrity of these dyes is checked and found to be stable. Their electronic properties also provide a good insight into their characteristics. Highest occupied molecular orbital (HOMO) energy level of the dyes is positioned under the redox potential of redox couple, , which means that the dyes can be regenerated. LUMO energy value of dyes with C30 and C10B10N10 lies above the conduction band of semiconductor, TiO2, and hence electrons from the excited state of the dyes can be injected into the conduction band edge of TiO2. For C10B10P10, lowest unoccupied molecular orbital (LUMO) lies slightly below the conduction band of TiO2 (for B3LYP functional). Therefore, few more configurations of C10B10P10 have been checked by replacing B and P atoms with C atoms. Notably, incorporation of solvent rules out this exception and all the dyes become eligible for electron regeneration also. Time‐dependent DFT (TDDFT) studies throw light on their photochemical properties, which is one of the interim criteria for any system getting selected as a dye in the DSSCs.

Studying VOC in lead free inorganic perovskite photovoltaics by tuning energy bandgap and defect density

In hybrid perovskite photovoltaics (hPPV) highest reported efficiency is ∼25.2%. However, stability and toxicity are major concern towards commercialization. To improve stability, various approaches were made by research communities. Utilizing inorganic perovskite photoactive materials is one such approach to improve stability. Toxic element ‘Pb’ can be substituted with suitable non-toxic elements such as ‘Sn’ without sacrificing efficiency and stability. In CsPbI3, replacing Sn in place of Pb results in the PCE of ∼13%. However, efficiency of this PV is lagging 12% as compared with hybrid perovskite PV. This difference should be overcome to compete with hPPV. To improve the efficiency of inorganic PPV various experimental strategies were adopted. In this study, SCAPS simulation was carried out on FTO/TiO2/CsSnI3/spiro-OMeTAD/Au by altering Eg, energetic position of conduction and valence band, defect density, and thickness of semiconductor. Obtained results were analyzed and reported in this work.