Cohesive‐Energy‐Resolved Bandgap of Nanoscale Graphene Derivatives

With a size‐dependent cohesive energy formula for two‐dimensional coordinated materials, the bandgap variation in quantum dots and nanoribbons of graphene derivatives, such as graphane, fluorographene and graphene oxides, is investigated. The bandgap is found to increase substantially as the diameter or width of the nano‐sized material decreases. The bandgap variation is attributed to the change in cohesive energy of edge carbon atoms, and is associated with the physicochemical nature and degree of edge saturation. These predictions agree with previously reported computer simulation results, and have potential application in wide‐band optics and optoelectronics.     

Synthesis of diketopyrrolopyrrole‐containing conjugated polyelectrolytes for naked‐eye detection of DNA

Two water‐soluble cationic conjugated polyelectrolytes ( P1 and P2 ) containing diacetylene, diketopyrrolopyrrole (DPP), and fluorene units were synthesized with Glaser‐Hay coupling reaction as the key step. The narrow bandgap DPP units and the wide bandgap fluorene units in the cationic polyelectrolytes might form an energy donor‐acceptor molecule architectures, in which DPP units serve as an acceptor of the fluorescent resonance energy transfer. The addition of calf thymus DNA enhances the fluorescent resonance energy transfer from fluoreneethynylene segments to DPP units, which results in a sensitive color change from blue to red in the PL spectra and allows naked‐eye detection of DNA with low concentration. In addition, the detection of DNA with P1 and P2 is high selective because it is not interfered by common ions. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Thermochemical solar hydrogen generation

Solar direct, indirect and hybrid thermochemical processes are presented for the generation of hydrogen and compared to alternate solar hydrogen processes. A hybrid solar thermal/electrochemical process combines efficient photovoltaics and concentrated excess sub-bandgap heat into highly efficient elevated temperature solar electrolysis of water and generation of H2 fuel utilizing the thermodynamic temperature induced decrease of E(H2O) with increasing temperature. Theory and experiment is presented for this process using semiconductor bandgap restrictions and combining photodriven charge transfer, with excess sub-bandgap insolation to lower the water potential, and their combination into highly efficient solar generation of H2 is attainable. Fundamental water thermodynamics and solar photosensitizer constraints determine solar energy to hydrogen fuel conversion efficiencies in the 50% range over a wide range of insolation, temperature, pressure and photosensitizer bandgap conditions.     

Role of Edge Geometry and Magnetic Interaction in Opening Bandgap of Low‐Dimensional Graphene

By using a size‐dependent cohesive energy formula for two‐dimensional coordination materials, the bandgap openings of ideal graphene quantum dots (GQDs) and nanoribbons (GNRs) have been investigated systematically regarding dimension, edge geometry, and magnetic interaction. Results demonstrate that the bandgap openings in GQDs can be dominated by the change of atomic cohesive energy. Relative to zigzag GQDs, the openings in the armchair ones are more substantial, attributed to its edge instability. The change of cohesive energy can also lead to bandgap openings in zigzag and armchair GNRs. The contribution from the interedge magnetic interaction in zigzag GNRs is negligible, while the cohesive‐energy induced openings in armchair GNRs can oscillate according to the so‐called full‐wavelength effect, depending on the width. The model prediction provides physicochemical insight into the bandgap openings in graphene.     

Anode interlayer in organic photovoltaics: Narrow bandgap small molecular materials as exciton‐blocking layer

Six materials were used as an interlayer at the anode side (anode interlayer [AIL]) of an archetypical planar heterojunction organic solar cell (OSC). In addition to two conventional wide bandgap hole transport materials (HTMs), tris(4‐carbazol‐9‐ylphenyl)amine ( TCTA ) and trans‐4,4′‐bis[N‐(naphthalen‐1‐yl)‐N‐phenylamino]stilbene ( NPAE ), we explore four narrow bandgap materials, bis(biphenylaminospiro)‐fumaronitrile ( PhSPFN ), bis(N‐(naphthalen‐1‐yl)‐N‐phenylamino)anthraquinone ( NPAAnQ ), bis‐(di(2‐fluorophenyl)aminospiro)‐fumaronitrile ( FPhSPFN ), and bis[4‐(N‐(pyren‐1‐yl)‐N‐phenylamino)phenyl]fumaronitrile ( PyPAFN ), the energy levels of which essentially align with the ones of SubPc, the active light‐absorbing material of the OSC study herein. By using a narrow bandgap AIL, universally enhanced short‐circuit current density and power conversion efficiencies (PCEs) have been achieved. In addition, one of these materials, FPhSPFN , results in a PCE of 5.13%, which is the highest reported value for SubPc solar cells with a similar architecture. This is ascribed to the formation of an otherwise passive exciton‐blocking interface. Furthermore, this demonstrates that charge selectivity by way of a high‐lying lowest unoccupied molecular orbital (LUMO) energy level is not a prerequisite for successful AIL design. As such, in terms of energy level alignment and bandgap energies, we establish a viable alternative approach toward interface and interlayer material design.     

Improving current and mitigating energy loss in ternary organic photovoltaics enabled by two well-compatible small molecule acceptors

Ternary organic photovoltaic(OPV)strategy is an effective but facile approach to enhance the photovoltaic performance for single-junction devices.Herein,a series of ternary OPVs were fabricated by employing a wide bandgap donor(PBDB-TF)and two acceptor-donor-acceptor(A-D-A)-type nonfullerene small molecule acceptors(NF-SMAs,called F-2 Cl and 3 TT-OCIC).As the third component,the near-infrared SMA,3 TT-OCIC,has complementary absorption spectrum,narrow bandgap and wellcompatible crystallization property to the host acceptor(F-2 Cl)for efficient ternary OPVs.With these,the optimal ternary devices yield significantly enhanced power conversion efficiency of 15.23%,one of the very few examples with PCE higher than15%other than Y6 systems.This is mainly attributed to the increased short-circuit current density of 24.92 m A cm^-2 and dramatically decreased energy loss of 0.53 e V.This work presents a successful example for simultaneously improving current,minimizing energy loss and together with modifying the morphology of active layers in OPVs,which will contribute to the further construction of high performance ternary OPVs.     

Separation of Electrical and Optical Energy Gaps: Selectively Adjusting the Electrical and Optical Properties for a Highly Efficient Blue Emitter

The design concept of separation of optical and electrical bandgap for wide bandgap materials is further developed in DCzSiPI. The HOMO/LUMO levels can be tuned by incorporation of PI and DCz substituents. The tetraphenylsilane core avoids the intramolecular charge transfer from DCz to PI (DCz=dimer carbazole, PI=phenanthro[9,10‐d]imidazole). The allowed transitions are found to be from HOMO?1 to LUMO providing DCzSiPI with sufficient bandgap.     

Quantitative analysis of structure and bandgap changes in graphene oxide nanoribbons during thermal annealing

Graphene oxide nanoribbons (GONRs) are wide bandgap semiconductors that can be reduced to metallic graphene nanoribbons. The transformation of GONRs from their semiconductive to the metallic state by annealing has attracted significant interest due to its simplicity. However, the detailed process by which GONRs transform from wide-bandgap semiconductors to semimetals with a near zero bandgap is unclear. As a result, precise control of the bandgap between these two states is not currently achievable. Here, we quantitatively examine the removal of oxygen-containing groups and changes in the bandgap during thermal annealing of GONRs. X-ray photoelectron spectroscopy measurements show the progressive removal of oxygen-containing functional groups. Aberration-corrected scanning transmission electron microscopy reveals that initially small graphene regions in GONRs become large stacked graphitic layers during thermal annealing. These structural and chemical changes are correlated with progressive changes in the electrochemical bandgap, monitored by cyclic voltammetry. These results show that small changes in the thermal annealing temperature result in significant changes to the bandgap and chemical composition of GONRs and provide a straightforward method for tuning the bandgap in oxidized graphene structures.     

Electrochemically Determining Electronic Structure of ZnO Quantum Dots with Different Surface Ligands

The electronic structure of quantum dots (QDs) including band edges and possible trap states is an important physical property for optoelectronic applications. The reliable determination of the energy levels of QDs remains a big challenge. Herein we employ cyclic voltammetry (CV) to determine the energy levels of three types of ZnO QDs with different surface ligands. Coupled with spectroscopic techniques, it is found that the onset potential of the first reductive wave is likely related to the conduction band edges while the first oxidative wave originates from the trap states. The determined specific energy levels in CV further demonstrates that the ZnO QDs without surface ligands mainly have oxygen interstitial defects whilst the ZnO QDs covered with ligands contain oxygen vacancies. The present electrochemical method offers a powerful and effective way to determine the energy levels of wide bandgap ZnO QDs, which will boost their device performance.     

Facile synthesis of wide-bandgap fluorinated graphene semiconductors

The bandgap opening of graphene is extremely important for the expansion of the applications of graphene-based materials into optoelectronics and photonics. Current methods to open the bandgap of graphene have intrinsic drawbacks including small bandgap openings, the use hazardous/harsh chemical oxidations, and the requirement of expensive chemical-vapor deposition technologies. Herein, an eco-friendly, highly effective, low-cost, and highly scalable synthetic approach is reported for synthesizing wide-bandgap fluorinated graphene (F-graphene or or fluorographene) semiconductors under ambient conditions. In this synthesis, ionic liquids are used as the only chemical to exfoliate commercially available fluorinated graphite into single and few-layer F-graphene. Experimental and theoretical results show that the bandgap of F-graphene is largely dependent on the F coverage and configuration, and thereby can be tuned over a very wide range.     

A non-fullerene acceptor enables efficient P3HT-based organic solar cells with small voltage loss and thickness insensitivity

The large D core of DFPCBR results in efficient P3HT-based OSCs with a high V_OC and thickness insensitivity.     

BiOI@La(OH)3纳米棒异质结制备及其增强可见光催化去除NO性能

一维La(OH)3纳米棒具有特殊的电子结构和多功能特性,特别是作为半导体光催化剂引起了人们极大的兴趣.但La(OH)3禁带宽度较大,且只能吸收紫外光,所以光催化效率较低,可见光利用能力较差,限制了La(OH)3的实际应用.因此,需要开发一种高效的改进方法来提高La(OH)3的可见光催化性能.本课题组发展了一种有效的改进La(OH)3方法,通过简易的方法将BiOI纳米颗粒沉积在La(OH)3纳米棒上,有效增强了对可见光的吸收能力和光生载流子的分离能力.本文采用X射线衍射(XRD)、透射电镜(TEM)、扫描电镜(SEM)、紫外-可见漫反射光谱(UV-Vis DRS)、荧光光谱(PL)、光电子能谱(XPS)、电子自旋共振(ESR)、N2吸附和元素分析等手段研究了BiOI@La(OH)3纳米棒异质结的构建原理及增强可见光催化性能的原因.XRD和XPS结果表明,通过简易化学沉积法原位构建了BiOI@La(OH)3异质结,并且在异质结中没有杂相生成.由SEM图像可见,原始La(OH)3由分散的一维纳米棒组成,平均直径为30–50 nm.通过BiOI与La(OH)3表面的紧密接触成功构建异质结,但BiOI纳米颗粒未改变La(OH)3纳米棒的形貌.由TEM和HRTEM图像可见,La(OH)3纳米棒的平均长度为30–50 nm,并且在BiOI@La(OH)3异质结中可以清晰看出BiOI和La(OH)3之间紧密接触的界面和晶格间距.N2物理吸附结果显示,随着BiOI量的增加,BiOI@La(OH)3异质结的比表面积增加,但孔体积未现明显变化.UV-Vis DRS结果显示,引入BiOI后明显促进了La(OH)3对可见光的吸收能力和利用效率,从而有利于增强可见光催化活性.通过理论计算分别得到BiOI和La(OH)3的价带和导带位置,表明具有非常匹配的能带结构可以促进BiOI光生电子的有效转移.可见光催化去除NO测试结果表明,BiOI@La(OH)3异质结的光催化活性高达50.5%,明显优于BiOI和La(OH)3.ESR测试结果显示,BiOI@La(OH)3异质结可见光催化活性中起主要作用的活性物种是?OH.结合表征结果,BiOI@La(OH)3纳米棒异质结可见光催化性能增强的原因主要有三个:(1)BiOI@La(OH)3异质结增大的比表面积有利于反应物和产物在催化剂表面扩散,同时可提供更多活性位点参与光催化反应;(2)禁带宽度影响光催化效率,当BiOI与La(OH)3达到合适比例时,既可以促进可见光吸收,也可以使光生电子具有较强还原能力;(3)BiOI@La(OH)3异质结有利于光生载流子的分离,从而显著提高其光催化活性.     

Tuning the electronic properties of conjugated polymer by tethering low‐bandgap rhenium(I) complex on the main chain

Low‐bandgap rhenium(I) complex with absorption onset at 795 nm in solution was tethered onto π‐conjugated polymer. The conjugated copolymer provides solution processability of the metallopolymer, and the pendant allows the low energy‐absorbing Re(I) complex units to be evenly distributed on the thin film. The copolymer tethered with low‐bandgap rhenium complex was synthesized by Suzuki cross‐coupling reaction. The metal‐free polymer ( poly‐1 ) tethered with functionalized intramolecular charge transfer dye, 2‐phenyl‐3‐pyridin‐2‐yl‐5,7‐di‐2‐thienylthieno[3,4‐b]pyrazine, exhibited high molecular weight, good film‐forming properties, and excellent solution processability. The pendants of the conjugated polymer possess donor–acceptor characters and broaden the absorption band. These pendants can function as bidentate ligands for metal chelation. The solubilizing groups on the monomers provide good solubility to the polymer even with high content of metal chelation. Upon the complexation with rhenium(I) pentacarbonyl chloride, the absorption spectrum of the resulting metallopolymer was further extended toward the near‐infrared region. Photovoltaic performances based on this metallopolymer have been studied. The design approach of these metallopolymers provides synthetic feasibility for coordinating wide range of metal ions on the pendant, and the resulting low‐bandgap polymer can be a potential candidate for light harvesting material in solar cell applications. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2311–2319, 2010     

Bi0·5K0·5TiO3-based lead-free relaxor ferroelectric with high energy storage performances via the grain size and bandgap engineering

Dielectric capacitors with high energy storage performance show a huge competitive advantage for use in vehicles and power electronics. Here, the (1-x) (0.75Bi_0·5K_0·5TiO₃?0.25BiFeO₃) – xSr_0.7Bi_0·2TiO₃ (BKT-BF-xSBT) materials were designed based on the dual optimization strategy of grain size and bandgap. The optimal performance was obtained in the BKT-BF-0.4SBT sample, achieving high energy storage density W_rec of 5.21 J/cm³ and high energy storage efficiency η of 90.87% at 360 kV/cm. The addition of SBT optimized the microstructure and relaxation behavior of BKT-BF ceramic, giving rise to the formation of polar nanoregions (PNRs), small grain size (G), compact grain boundaries, and wide bandgap (E_g) synchronously. Encouragingly, prominent stabilities against temperature, frequency, and cycle numbers, and favorable charge/discharge performance (power density P_D ≈ 64.5 MW/cm³, τ_0.9 ≈ 90 ns) are also accomplished in designed BKT-based ceramics. These findings indicate that the BKT-BF-xSBT ceramic system has excellent potential in the dielectric energy storage field and also provides a viable prospect for engineering design of high-efficiency lead-free dielectrics via bandgap and grain size.     

Preparation and Characterization of Peroxo Titanic Acid Solution Using TiCl3

The peroxo titanic acid solution was successfully prepared using titanium trichloride as a precursor. The basic properties of the TiO₂ film prepared by the solution were investigated in view of phase change, bandgap energy, crystalline size etc. The film displayed amorphous TiO₂ at room temperature, anatase above 281°C and a mixture of anatase and rutile at 990°C. The crystalline size increases with annealing temperatures, while the bandgap energies decrease due to the quantum size effect and the formation of rutile phase which has low bandgap energy. As a result of TG-DTA, it was found that annealing treatment at 990°C for 2 h formed a mixture of anatase and rutile through three steps: (1) the removal of physically adsorbed water (2) the decomposition of peroxo group (3) amorphous-anatase or anatase-rutile phase transformation.     

Advances in transition metal dichalcogenide-based two-dimensional nanomaterials

Two-dimensional transition metal dichalcogenides (TMDCs) are the layered materials that have gained substantial consideration in a wide range of applications. The TMDCs possess exceptional properties such as high surface-to-volume ratio, excellent charge transfer capacity, mechanical strength, and low bandgap energy. Additionally, TMDCs (MoS₂, WS₂, etc.) are abundant, have a low synthesis cost, and are visible-light-active. The appealing surface morphologies and properties of TMDCs make them an appropriate choice for diverse applications like photocatalytic degradation of hazardous pollutants, energy conversion reactions (electrocatalytic and photocatalytic H₂ production), and energy storage devices (supercapacitors and rechargeable batteries) in addition to bio/chemical sensors. This article addresses the latest trends and advancements in the domain of TMDC-based nanomaterials. The different synthesis routes have been comprehensively reviewed. The challenges faced by TMDCs at a large scale and the future scope have also been discussed.     

Fabrication of FeOOH/BiOCl Nanocomposites with Enhanced Visible Light Photocatalytic Activity

BiOCl as a two‐dimensional layer ternary oxide semiconductor, has been widely used in energy and environmental area due to its non‐toxicity, price and the good photocatalytic performance. However, BiOCl has a wide bandgap and can only absorb ultraviolet light, which limits its solar energy conversion efficiency for practical application. Herein, we report a facile synthesis of FeOOH/BiOCl nanocomposites by hydrothermal method. The results of XPS and FT‐IR indicated that FeOOH has been loaded on the nanocomposites. The chemical and optical properties of the nanocomposite are well‐characterized. The nanocomposite showed much more excellent photocatalytic performance compared with the individual FeOOH and BiOCl single component. Reactive specie trapping experiment indicated that · O^2– and h⁺ were the two main active species during the photocatalytic process of FeOOH/BiOCl nanocomposites.     

非富勒烯聚合物太阳电池研究进展

综述了以p-型共轭聚合物为给体、n-型有机半导体为受体的非富勒烯聚合物太阳电池光伏材料最新研究进展,包括n-型共轭聚合物和可溶液加工小分子n-型有机半导体(n-OS)受体光伏材料,以及与之匹配的p-型共轭聚合物给体光伏材料.介绍的n-型共轭聚合物受体光伏材料包括基于苝酰亚胺(BDI)、萘酰亚胺(NDI)以及新型硼氮键连受体单元的D-A共聚物受体光伏材料,目前基于聚合物给体(J51)和聚合物受体(N2200)的全聚合物太阳电池的能量转换效率最高达到8.26%.n-OS小分子受体光伏材料包括基于BDI和NDI单元的有机分子、基于稠环中心给体单元的A-D-A型窄带隙有机小分子受体材料等.给体光伏材料包括基于齐聚噻吩和苯并二噻吩(BDT)给体单元的D-A共聚物,重点介绍与窄带隙A-D-A结构小分子受体吸收互补的、基于噻吩取代BDT单元的中间带隙二维共轭聚合物给体光伏材料.使用中间带隙的p-型共轭聚合物为给体、窄带隙A-D-A结构有机小分子为受体的非富勒烯聚合物太阳电池能量转换效率已经突破12%,展示了光明的前景.最后对非富勒烯聚合物太阳电池将来的发展进行了展望.     

One-pot construction of S–Mo co-doped BiOCl toward simultaneously decreasing size,tuning energy band structure,and promoting charge separation for efficient photocatalytic degradation of organic pollutants

Bismuth oxychloride (BiOCl), although it has exhibited intensely potential used in photocatalyst for environmental remediation, owns wide bandgap and the fast photocharge recombination that limits its effective application. Doping BiOCl used in metal and non-metal elements simultaneously, as a feasible strategy in designing novel visible-light photocatalysts, was conductive to effectively overcome the as-above defects. The present work constructed S-Mo co-doped BiOCl-- with abundant reactive sites via one-pot hydrothermal method. The as-prepared S–Mo co-doped BiOCl sample presents the best-visible light-driven photodegradation performance, and its kinetic constant (k) is about 16.8 times (for rhodamine B) and 6.5 times (for tetracycline hydrochloride) higher than that of pure BiOCl, respectively. By contrast, S-Mo co-dopant induced the decrease of nanosheets size and endowed the large specific surface areas, which favors the increased reactive sites. Further analysis with the aid of experiments and density function theory calculations indicated that the intermediate level induced by S 2p orbitals could narrow the bandgap and promote the excitation of electron from conduction band to valance band via providing the middle springboard on the one hand, and the Mo energy states was conducive to promote the separation of charge carriers by acted as the acceptor for the photoinduced electrons on the other hand. Consequently, the potential origin of the improved visible-light-driven performance lies in the more superoxide radicals for oxidizing organic pollutants caused by the simultaneous enhancement of visible light absorption as well as charge separation resulted from the further optimization of energy band structure that associated with the doping energy level of S-Mo co-doping in BiOCl. This work demonstrated that S and Mo co-doping BiOCl is of highly promising candidate for the further progress of environmental remediation.     

Characterization and optical properties of mechanochemically synthesized molybdenum-doped rutile nanoparticles and their electronic structure studies by density functional theory

The optical and electronic properties of molybdenum (Mo) doped rutile TiO₂ prepared by the mechanochemical method were studied both experimentally and using density functional theory (DFT). The synthesized nanoparticles were characterized by XRD, TEM, EDS-MAP, and XPS. The XRD results showed the successful incorporation of Mo in the rutile crystal lattice. High-resolution TEM images illustrated a decreasing trend in the (110) d-spacing for samples doped up to 3 at%. The shift toward higher binding energies in the XPS spectra was due to the higher oxidization tendencies of Mo⁵⁺ and Mo⁶⁺ substituted in Ti⁴⁺ sites. The optical behavior of samples was examined by UV–Vis and photoluminescence spectroscopy. The bandgap energy value of rutile was reduced from 3.0 eV to 2.4 eV by 2 at% Mo doping. The DFT calculations showed a reduction of bandgap energy value of rutile to 2.35 eV with 2 at% Mo, which is in harmony with the experimental results. The creation of energy states below the conduction band because of Mo doping was identified as the reason for reducing the bandgap energy and photoluminescence emission of rutile.