Band-edge Levels Research Articles

On analysis of structural and optical absorption characterization of Bi35Sb5Se60 nanostructured thin films for photosensing application

In this extensive study, the primary focus is directed towards the intricate exploration of the optical absorption characteristics inherent in nanostructured Bi35Sb5Se60 thin films, prepared by thermal evaporation under a vacuum of 10−5 Torr, ensuring high purity and uniformity for optoelectronic applications. With a particular emphasis on their prospective application in photosensing devices. The research employs a comprehensive approach, integrating various spectrophotometric measurements that encompass both transmission and reflection analyses. The meticulous examination of the absorption edge characteristics reveals a direct energy gap of 1.82 eV, providing a foundational understanding of the material's electronic structure. The determination of the dispersion energy at 6.35 eV and the oscillator energy at 2.96 eV further enriches the understanding of the material's optical behavior, shedding light on its capacity to interact with incident light. A noteworthy highlight emerges with the identification of high photosensitivity exhibited by the heterojunction, particularly under lower reverse bias conditions, underscoring its potential utility in photosensing applications. The PL spectra reveal a highly broadened defect emission band with peaks at 475 nm, 490 nm, and 540 nm, providing insights into the recombination processes within the material. The identification of emission peaks related to the conduction band edge and acceptor levels further enhances the comprehension of the material's optical and electronic characteristics. underscores the potential of these nanostructured thin films for efficient photosensing devices. The findings presented in this research not only advance the understanding of the material's properties but also lay a robust foundation for further research and development in the design and optimization of photoresponsive devices within the realm of optoelectronic technologies.

Engineering MOF-derived 2D NPC-TiO2 nanotablet/3D marigold-like ZnIn2S4/CdS nanoparticles dual Z-scheme heterojunction with excellent photoelectric performance: A novel material for sensitive and facile photoelectrochemical sensing detection of mercury ions in aqueous environments by ion-exchange sensing strategy

Herein, a new NH2-MIL-125-derived 2D nitrogen-doped porous carbon-titanium dioxide (NPC-TiO2) nanotablet/3D marigold-like ZnIn2S4/CdS nanoparticles (NPs) dual Z-scheme heterojunction was first exploited for photoelectrochemical (PEC) measurement of mercury ions (Hg2+). Taking NH2-MIL-125 as precursor, the 2D NPC-TiO2 nanotablet was prepared by calcination. The 3D marigold-like ZnIn2S4 and CdS NPs were synthesized by hydrothermal method and aqueous synthesis way, respectively. The acquired NPC-TiO2, ZnIn2S4 and CdS were sequentially modified on the indium tin oxide (ITO) electrode to form the PEC sensing interface by layer-by-layer assembly. Due to the matched band-edge levels, and strong light-harvesting ability, the given heterostructure on ITO electrode generated a large photocurrent. Importantly, it was found that 2D NPC-TiO2 nanotablet/3D marigold-like ZnIn2S4/CdS NPs dual Z-scheme heterojunction could show specifically increased photocurrent signal towards to Hg2+ by employing CdS NPs as Hg2+-recognition probe with selective Cd-to-Hg ion-exchange, resulting from the in-situ formation of the new quaternary NPC-TiO2/ZnIn2S4/CdS/HgS heterostructure to further facilitate the spatial transmission and separation of charges. As a result, Hg2+ was highly sensitively detected with a low detection limit of 20 fM. This PEC sensor was also verified by evaluating Hg2+ in tap water, river water and lake water, demonstrating great application prospect for environment pollutant measurement.

Band-Edge Energy Levels of Dynamic Excitons in Cube-Shaped CdSe/CdS Core/Shell Nanocrystals.

An electron-hole pair in a cube-shaped CdSe/CdS core/shell nanocrystal exists in the form of dynamic excitons across the strongly and weakly confined regimes under ambient temperatures. Photochemical doping is applied to distinguish the band-edge electron and hole levels, confirming an effective mass model with universal constants. Reduction of the optical bandgap upon epitaxy of the CdS shells is caused by lowering the band-edge electron level and barely affecting the band-edge hole level. Similar shifts of the electron levels, yet retaining the hole levels, can switch the order in energy of the three lowest-energy transitions. Thermal distribution of 1-4 electrons among the two thermally accessible electron levels follows number-counting statistics, instead of Fermi-Dirac distribution.

PEC-SERS Dual-Mode Detection of Foodborne Pathogens Based on Binding-Induced DNA Walker and C3N4/MXene-Au NPs Accelerator.

In this paper, a photoelectrochemical (PEC)-surface-enhanced Raman scattering (SERS) dual-mode biosensor is constructed coupled with a dual-recognition binding-induced DNA walker with a carbon nitride nanosheet (C3N4)/MXene-gold nanoparticles (C/M-Au NPs) accelerator, which is reliable and capable for sensitive and accurate detection of Staphylococcus aureus (S. aureus). Initially, a photoactive heterostructure is formed by combining C3N4 and MXene via a simple electrostatic self-assembly as they possess well-matched band-edge energy levels. Subsequently, in situ growth of gold nanoparticles on the formed surface results in better PEC performance and SERS activity, because of the synergistic effects of surface plasmon resonance and Schottky barrier. Furthermore, a three-dimensional, bipedal, and dual-recognition binding-induced DNA walker is introduced with the formation of Pb2+-dependent DNAzyme. In the presence of S. aureus, a significant quantity of intermediate DNA (I-DNA) is generated, which can open the hairpin structure of Methylene Blue-tagged hairpin DNA (H-MB) on the electrode surface, thereby enabling the switch of signals for the quantitative determination of S. aureus. The constructed PEC-SERS dual-mode biosensor that can be mutually verified under one reaction effectively addresses the problem of the low detection accuracy of traditional sensors. Experimental results revealed that the effective combination of PEC and SERS is achieved for amplification detection of S. aureus with a detection range of 5-108 CFU/mL (PEC) and 10-108 CFU/mL (SERS), and a detection of limit of 0.70 CFU/mL (PEC) and 1.35 CFU/mL (SERS), respectively. Therefore, this study offers a novel and effective dual-mode sensing strategy, which has important implications for bioanalysis and health monitoring.

Novel two-dimensional square-AlAs: Direct semiconductor coupled with high electron-hole mobility ratio toward sunlight-driven water-splitting

The design of new monolayered atomic motifs always attracts enormous attention due to their interesting properties induced by unique crystal phases and promising catalytic applications in low dimensional devices. Herein, we propose a novel square-AlAs monolayer based on ab initio density functional theory calculations, whose good stability is confirmed from the perspectives of energy, dynamics, thermodynamics, and mechanics. Electronic structure calculations reveal that the newly predicted square-AlAs monolayer is a direct-gap semiconductor with a bandgap of 1.39 eV, which is sensitive to in-plane strain, meanwhile the strain induced changes in bandgap allow advantageous modulations of optical absorption in visible-light region. Unfortunately, the unfavorable hydrogen evolution reaction (HER) band edge levels make square-AlAs not suitable for photocatalytic water-splitting in spite of the appropriate bandgap, high electron-hole mobility ratio and strong visible light absorption. However, a favorable effect caused by strain engineering is revealed by the fact that the square-AlAs can meet the requirement of photocatalytic water-splitting under the suitable biaxial loading. Particularly, compared to pure AlAs, the Gibbs free energy of hydrogen adsorption indicate that Boron-doping can effectively decrease the HER overpotential. Moreover, the external potential provided by photoexcited electrons for oxygen evolution reaction (OER) is quite positive, which can serve as a free and pollution-free driving force to drive OER to proceed spontaneously for pure AlAs or reduce the OER overpotential to a very low value (0.15 V) for Boron-doped AlAs, overmatching widely used IrO2 catalyst.

Photocatalytic degradation of antibiotic sulfamethizole by visible light activated perovskite LaZnO3

In this work, the perovskite LaZnO3 was synthesized via sol-gel method and applied for photocatalytic treatment of sulfamethizole (SMZ) antibiotics under visible light activation. SMZ was almost completely degraded (99.2% ± 0.3%) within 4 hr by photocatalyst LaZnO3 at the optimal dosage of 1.1 g/L, with a mineralization proportion of 58.7% ± 0.4%. The efficient performance of LaZnO3 can be attributed to its wide-range light absorption and the appropriate energy band edge levels, which facilitate the formation of active agents such as ·O2−, h+, and ·OH. The integration of RP-HPLC/Q-TOF-MS and DFT-based computational techniques revealed three degradation pathways of SMZ, which were initiated by the deamination reaction at the aniline ring, the breakdown of the sulfonamide moieties, and a process known as Smile-type rearrangement and SO2 intrusion. Corresponding toxicity of SMZ and the intermediates were analyzed by quantitative structure activity relationship (QSAR), indicating the effectiveness of LaZnO3-based photocatalysis in preventing secondary pollution of the intermediates to the ecosystem during the degradation process. The visible-light-activated photocatalyst LaZnO3 exhibited efficient performance in the occurrence of inorganic anions and maintained high durability across multiple recycling tests, making it a promising candidate for practical antibiotic treatment.

Enhanced Photocatalytic Water Splitting of SrTiO3 Perovskite through Cobalt Doping: Experimental and Theoretical DFT Understanding.

Throughout extensive research endeavors, SrTiO3 has emerged as a promising photocatalytic material for utilizing solar energy and facilitating hydrogen production via water splitting. Yet, the pursuit of enhanced efficiency and amplified hydrogen generation has prompted researchers to delve into the realm of advanced doping strategies. In this work, using experimental characteristics and DFT calculations, we studied the effect of cobalt substitution on the structural, electronic, optical, and magnetic properties as well as the photocatalytic activity of SrTi1-xCoxO3-δ (x = 0, 0.125, 0.25, 0.375, and 0.5) perovskites. The samples were successfully prepared by using the solid-state reaction method. Based on X-ray diffraction and the Rietveld refinement method, the elaborated samples were shown to preserve the absorption range up to the visible region. Moreover, the position of band edge levels after cobalt doping becomes more appropriate for water splitting. Our findings report that all cobalt-doped compounds exhibit good photocatalytic activities and could be used as suitable photocatalyst materials for hydrogen production.

Curvature-controlled band alignment transition in 1D van der Waals heterostructures

The effect of curvature on the band alignment of one-dimensional (1D) van der Waals (vdW) transition metal dichalcogenide (TMDC) heterostructures is studied by comprehensive first-principles calculations. We find that, as the diameter of a TMDC nanotube decreases, the combined effect of curvature-induced flexoelectricity and circumferential tensile strain causes a rapid lowering of the conduction band minimum, whereas the valence band maximum exhibits an initial lowering before rising. As individual TMDC nanotubes form coaxial heterostructures, the concerted effect of diameter-dependent band-edge levels and intertube coupling via flexovoltage can result in a transition of intertube band alignment from Type II to Type I in multiple heterostructural systems, including large-diameter MoSe2@WS2, MoTe2@MoSe2, and MoTe2@WS2 heterostructures. These results lay down a foundation for the rational design of 1D vdW heterostructures.

CdSe@CdS quantum dot-sensitized Au/α-Fe2O3 structure for photoelectrochemical detection of circulating tumor cells.

Circulating tumor cells (CTCs) are the important biomarker for cancer diagnosis and individualized treatment. However, due to the extreme rarity of CTCs (only 1-10 CTCs are found in every milliliter of peripheral blood) high sensitivity and selectivity are urgently needed for CTC detection. Here, a sandwich PEC cytosensor for the ultrasensitive detection of CTCs was developed using thephotoactive material Au NP/-Fe2O3 and core-shell CdSe@CdS QD sensitizer. In the proposed protocol, theCdSe@CdS QD/Au NP/α-Fe2O3-sensitized structure with cascade band-edge levels could evidently promote the photoelectric conversion efficiency due to suitable light absorption and efficient electron-hole pair recombination inhibition. Additionally, a dendritic aptamer-DNA concatemer was constructed for highly efficient capture of MCF-7 cells carrying CdSe@CdS QDs, a sensitive material. The linear range of this proposed signal-on PEC sensing method was 300 cell mL-1 to 6 × 105 cell mL-1 with a detection limit of 3 cell mL-1, and it demonstrated an ultrasensitive response to CTCs. Furthermore, this PEC sensor enabled accurate detection of CTCs in serum samples. Hence, a promising strategy for CTC detection in clinical diagnosis was developed based on CdSe@CdS QD-sensitized Au NP/α-Fe2O3-based PEC cytosensor with dendritic aptamer-DNA concatemer.

Efficient heterostructure of MoS2/Ti-doped Fe2O3 nanorods for high-performance photoelectrochemical activity

The unique nanoflakes/nanorods heterostructure of MoS2/Ti-Fe2O3 was designed to boost the photoelectrochemical (PEC) performance of Fe2O3 nanorods through Ti doping and MoS2 nanoflake coating. The MoS2/Ti-Fe2O3 heterostructure photoelectrode exhibited significantly improved PEC performance, with a photocurrent density 15-fold higher than that of the Fe2O3 photoelectrode. Along with the concordance of band gap and band edge levels between Fe2O3 and MoS2, the enhanced PEC performance can be explained by the efficient charge separation and transfer in the MoS2/Ti-Fe2O3 heterostructure. These results offer new opportunities for Fe2O3-based nanostructures in constructing high-performance solar energy-driven devices.

Metal-free Janus α- and β-SiCP4: designing stable and efficient two-dimensional semiconductors for water splitting.

Two-dimensional (2D) semiconductors exhibit exceptional potential in the field of photocatalytic water splitting due to their unique structural characteristics and photoelectric properties. In this study, based on first-principles density functional theory, we theoretically proposed two SiCP4 Janus 2D semiconductors with high stability, namely monolayer α- and β-SiCP4. By performing the calculation of HSE06 functionals, the band structures of monolayer α- and β-SiCP4 have been estimated, and the results show that both α- and β-SiCP4 are direct-band-gap semiconductors with band gaps of 1.64 eV and 1.91 eV, respectively. Meanwhile, the band edge levels of monolayer α- and β-SiCP4 meet the band structure requirements of photocatalysts in water splitting. Notably, because of the internal build-in electric fields and tiny band gaps, monolayer α- and β-SiCP4 exhibit separated photogenerated electron-hole pairs and high solar-to-hydrogen (STH) efficiency, reaching up to 33.68% and 23.72%, respectively. Additionally, we also investigate the impact of uniaxial strain on electronic, optical and photocatalytic properties of monolayer α- and β-SiCP4 considering pH values ranging from 0 to 14. Our results demonstrate that the maximum STH efficiency for α-SiCP4 is achieved under X-direction strain (η) of 2%, Y-direction strain (η) of 8%, and pH values between 2 and 4. Conversely, β-SiCP4 exhibits the highest STH efficiency under X-direction strain (η) of 8%, Y-direction strain (η) of 6%, and pH values between 2 and 4.

Photocatalytic activity of MoS2 with water monolayers: Global optimization.

Atomically thin MoS2 has emerged to be promising for photocatalytic water splitting benefiting from its suitable geometrical and electronic structure for light harvesting. A better understanding of how water molecules affect the band edge levels of MoS2 is critical for promoting the interfacial reactivity. Here, we determine the structures of water monolayers on MoS2 using global optimizations achieved by molecular dynamics in combination with local minimization. It is shown that cyclic water clusters are formed on a surface through a hydrogen-bonding network. The absolute band edge positions are explored taking into account the derivative discontinuity of the exchange-correlation functional. Shifts in band edges are observed with the increase in H2O coverage, while bandgaps tend to be slightly decreased. In particular, the band alignment relative to water redox potentials has been investigated in detail. We find that the dimer configuration is likely to suppress the hydrogen evolution reaction (HER), while the polygon clusters lift the conduction band by 0.2-0.7eV, and thus, they would enhance HER. This effect is explained in terms of the linear dependence of the band edge offset on an interface electric dipole arising from water assemblies.

Designing limiting-efficiency BaSi[formula omitted] solar cells by device simulation and computational material screening

A double heterojunction solar cell consisting of a solar absorber and electron/hole transport layers (ETL/HTL) is ideally efficient and can contribute to the exploitation of solar energy. BaSi2 is an attractive solar absorber material possessing a band gap of 1.3 eV and high absorption coefficients. However, finding proper ETL/HTL materials remains challenging. Here, limiting efficiency calculation, device simulation, and computational material screening are combined to design BaSi2 solar cells of near-limiting efficiency (> 28%). The limiting efficiency is calculated considering radiative and trap-assisted Auger recombinations, which shows that the Lambertian limit efficiency (32%) exceeds that of Si cells. Device simulations of double heterojunction BaSi2 cells were performed with different values of band gap, ionization potential, and electron affinity, which yields criteria for band-edge energy levels of the ETL and HTL. Candidate materials for the ETL and HTL are identified from the Materials Project database by three-step screening. The first step screens the materials for band gap, interface reactivity, lattice matching, etc. The second step is a literature survey to exclude air-sensitive or unstable materials under ambient conditions. In the third step, band-edge levels are calculated using density functional theory, and eight ETL and seven HTL candidate materials are identified. This device design method is applicable to any solar absorber material and promotes accelerated solar cell development.

Anomalous Emission Shift of CdSe/CdS/ZnS Quantum Dots at Cryogenic Temperatures.

The band-gap energy of most bulk semiconductors tends to increase as the temperature decreases. However, non-monotonic temperature dependence of the emission energy has been observed in semiconductor quantum dots (QDs) at cryogenic temperatures. Here, using stable and highly efficient CdSe/CdS/ZnS QDs as the model system, we quantitatively reveal the origins of the anomalous emission red-shift (∼8 meV) below 40 K by correlating ensemble and single QD spectroscopy measurements. About one-quarter of the anomalous red-shift (∼2.2 meV) is caused by the temperature-dependent population of the band-edge exciton fine levels. The enhancement of electron-optical phonon coupling caused by the increasing population of dark excitons with temperature decreases contributes an ∼3.4 meV red-shift. The remaining ∼2.4 meV red-shift is attributed to temperature-dependent electron-acoustic phonon coupling.

Highly sensitive photoelectrochemical neuron specific enolase analysis based on cerium and silver Co-Doped Sb2WO6

A signal-enhanced photoelectrochemical immunoassay technique for detecting neuron specific enolase (NSE) was proposed. As a photoactive matrix, (Ce,Ag):Sb2WO6 was firstly investigated via doping Ce and Ag into Sb2WO6. It could be found that the presence of Ce and Ag not only had enormous variation on the morphology of Sb2WO6, but also showed excellent PEC behavior. In order to further improve the visible light utilization rate of (Ce,Ag):Sb2WO6, In2S3 was modified onto the surface of (Ce,Ag):Sb2WO6 to enhance visible light absorption. In addition, the CdS/PDA was served as a secondary antibody marker to further amplify signal. Especially, PDA as an electron donor could effectively remove photogenerated holes. Meanwhile, the good matching cascade band-edge levels between CdS and Sb2WO6 could promote photoelectron migration, improve the PEC response, and achieve sensitive detection of NSE. Under the selected excellent conditions, the photocurrent can linearly increase with the increase of NSE concentration in the operating range from 0.1 pg/mL to 50 ng/mL, and the limit of detection is 1.57 fg/mL. The constructed immunosensor also exhibits satisfactory stability, selectivity, and reproducibility, and it creates conditions for the detection of other biomolecules.

Tungsten Trioxide Photoanode-Palladium Cathode Cell for Solar Seawater Splitting

N-type semiconductor-tungsten trioxide (WO3) finds application in a large variety of fields including photocatalysis, gas sensors, smart windows or as a substrate for heterogeneous catalysts. This presentation will focus on recent improvements in optoelectronic and photoelectrochemical (PEC) properties of WO3 thin films achieved in our laboratory. The semitransparent WO3 films are formed on F-doped tin oxide (FTO) conductive glass substrates, using a sol-gel method, by depositing the precursor layer-by-layer and annealing sequentially in the flow of oxygen. Use of appropriate mixtures of tungstic acid and organic structure-directing agents that form the WO3 film precursor, combined with a two-step annealing, allows the formation of highly crystalline nanostructured (NS) electrodes with controlled, large porosity. This renders possible the permeation of the whole mesoporous film by the electrolyte. Annealing of the as-deposited samples in oxygen above 500°C ensures structural ordering with formation of monoclinic WO3. Since none among photostable (metallic oxide) semiconductors exhibits band-edge energy levels that match those of hydrogen and oxygen evolution reactions to allow unassisted water splitting, the present efforts focus on minimizing the bias voltage required to perform visible light-driven photooxidation of water. In fact, a bias voltage of the order of 1 V may be provided by several single-junction PV cells likely to operate in a tandem device with the PEC cell. Despite visible-light absorption range of the WO3 films restricted to 500 nm, under standard conditions, i.e. at 1.23 V vs RHE and under simulated AM 1.5G solar light (100 mW/cm2), stable anodic water splitting photocurrents exceeding 4.5 mA/cm2 are regularly attained.This presentation will principally focus on photoelectrolysis experiments employing synthetic seawater electrolyte, in a two compartment (separated by a sintered glass diaphragm) cell, that showed dominant (with 60-70% Faradaic efficiency) formation of chlorine at the WO3 photoanode with remarkably stable photocurrents reaching 4.7 mA/cm2. In fact, as demonstrated in an earlier work from our laboratory1, the WO3 photoelectrodes exhibit preferentially oxidation of anions (including Cl-) of the acidic aqueous electrolytes. However, in contrast with the Cl- ions, the photooxidation of oxy-anions of acidic electrolytes leads generally to the "passivation" of the WO3 electrodes due to the formation of the surface layers of peroxo species.1 The only identified exception is the methane-sulfonic acid that allows oxygen generation at the WO3 photoanode with large stable photocurrents.2 In the case of seawater photoelectrolysis, the operating potential point at which the photocurrent approaches saturation occurs at ca 0.4 V below E(Cl-/Cl2)=1.36 V vs SHE. Consistently, the incident photon conversion efficiencies (IPCEs) reach a maximum of 85% over 390-410 nm range of wavelengths.3 Good mechanical and chemical stability of the WO3 electrodes in the presence of chlorine evolved from seawater was confirmed by monitoring the photocurrents over a 20 hours-long continuous photoelectrolysis runs.A schematic diagram of the seawater splitting PEC cell, including a NS WO3 film photoanode and a Pd sheet cathode, used in our experiments is shown below.Fig. 1 Schematic diagram of the seawater splitting PEC cell.The current of CO2 gas passing through the seawater represents a possible option for maintaining slightly acidic pH in the cathodic cell compartment. The important advantage of the adopted PEC cell configuration is to circumvent the problem of gas separation, i.e. chlorine/oxygen formed at the photoanode and hydrogen generated at the Pd cathode that is stored in the form of a Pd-H hydride. The storage of hydrogen generated in a PEC water splitting device in the form of a hydride, opens the possibility of its subsequent use as an anode in a hydride-oxygen battery.Such sunlight-driven PEC seawater splitting device can be implemented in remote places to provide on-site relatively small amounts of chlorine for disinfecting purposes including purification of drinking water.More generally, the prospect of using seawater electrolyte for a larger scale PEC hydrogen generation would release the strain on vital fresh water resources. Considering relatively low concentration of Cl- ions in seawater, roughly equivalent to 0.5 M NaCl, the photoelectrolysis delivering photocurrents in the range of mA/cm2 appears well suited for such applications.

Unraveling the Emission Pathways in Copper Indium Sulfide Quantum Dots.

Semiconductor copper indium sulfide quantum dots are emerging as promising alternatives to cadmium- and lead-based chalcogenides in solar cells, luminescent solar concentrators, and deep-tissue bioimaging due to their inherently lower toxicity and outstanding photoluminescence properties. However, the nature of their emission pathways remains a subject of debate. Using low-temperature single quantum dot spectroscopy on core-shell copper indium sulfide nanocrystals, we observe two subpopulations of particles with distinct spectral features. The first class shows sharp resolution-limited emission lines that are attributed to zero-phonon recombination lines of a long-lived band-edge exciton. Such emission results from the perfect passivation of the copper indium sulfide core by the zinc sulfide shell and points to an inversion in the band-edge hole levels. The second class exhibits ultrabroad spectra regardless of the temperature, which is a signature of the extrinsic self-trapping of the hole assisted by defects in imperfectly passivated quantum dots.

Electron Delocalization and Structure Coupling Promoted π-Conjugated Charge Transport in a Novel [Ga-Tpy2]PbI5 Perovskite-like Single Crystal.

Multidimensional perovskite techniques are of intense research interest since they are proved to be advantageous to enhance the perovskite stability. Thereinto, the structure engineering strategy has been widely used to regulate the low dimensional (LD) perovskite structures and obtain expected optoelectronic properties. In this work, we intercalate a thus far unreported metallic coordination compound [Ga-Tpy2]3+ (Tpy: 2,2';6',2″-terpyridine) to the inorganic Pb-I building block as the A-site organic group, and the zero dimensional (0D) [Ga-Tpy2]PbI5 perovskite-like single crystal is obtained. This material displays suitable band edge levels, which enable its potential application as light absorber in solar cells. The DFT calculations manifest delocalized charge distribution on Tpy ligands that can facilitate electron transport, which is attributed to the formation of a double hybrid coordinate bond, i.e., σ bonds and π bonds, between Ga3+ ions and Tpy ligands. These coordinate bonds make metallic complexes promising molecules to regulate structure-associated optoelectronic performances of the LD perovskites.

3‐2: Invited Paper: Instability Issues of LTPS TFT for High Performance of Flexible AMOLED Display

We present here a combined theoretical and experimental investigation on hysteresis improvement of LTPS TFTs via optimizing hydrogen content in poly‐silicon and adjusting density of states at poly‐Si/oxide interface. It can be demonstrated that hysteresis seems to be more dependent on the difference in trap density between the bandedge and midgap energy levels. A new method named just noticeable current difference (JND_Current) is employed to evaluate TFT reliability and short‐term image sticking. Incorporating the optimized processes of a‐Si deposition, cleaning conditions before gate‐insulator (GI) deposition and contact hole annealing is helpful to improve instability of LTPS TFTs. The hysteresis level (ΔVth) can be reduced to 0.11V, and also an improvement in quantized level of short‐term image sticking by 35%.

Hybrid Organic/Inorganic Photocathodes Based on WS2 Flakes as Hole Transporting Layer Material

The efficient production of molecular hydrogen (H2) is a fundamental step toward an environmentally friendly economy. Photocathodes using organic bulk heterojunction (BHJ) films as light harvesters represent an attracting technology for low‐cost photoelectrochemical water splitting. These photocathodes need charge transporting layers (CTLs) to efficiently separate and transport either holes or electrons toward the back‐current collector and electrolyte, respectively. Therefore, it is pivotal to control the energy band edge levels and the work function (WF) of the CTLs to match the ones of the BHJ film, current collector, and electrolyte. Herein, the use of 2D p‐doped WS2 flakes as hole transporting material for H2‐evolving photocathodes based on the regioregular poly(3‐hexylthiophene):phenyl‐C61‐butyric acid methyl ester (rr‐P3HT:PCBM) BHJ film is proposed. The WS2 flakes are produced through scalable liquid‐phase exfoliation of the bulk crystal, whereas p‐type chemical doping allows the tuning of the WS2 WF. This approach boosts the performances of the photocathodes, reaching photocurrent densities up to 4.14 mA cm−2 at 0 V versus reversible hydrogen electrode (RHE), an onset potential of 0.66 V versus RHE, and a ratiometric power‐saved metric of 1.28% (under 1 sun illumination). To the best of the authors' knowledge, these performances represent the current record for 2D materials‐based CTLs.