Solidification of silicon for electronic and solar applications

Silicon is widely used for its semiconducting properties in electronic and photovoltaic devices. These applications require strict control of the structure and impurity levels. Silicon must, therefore, be solidified using processes that give a minimum of impurity contamination and microstructural defects, as well as a planar solidification front to avoid microsegregation. Czochralski growth, and to some extent float zone crystallization, are processes used to obtain defect-free single crystals for integrated circuits and advanced solar cell wafers, whereas the Bridgman process can be used for production of multicrystalline silicon for standard solar cells. Direct solar cell wafer solidification processes have also been developed and reached limited commercial use. The paper will review these silicon crystallization processes and discuss recent developments and trends.     

Positive and negative magnetic field effects in organic semiconducting materials

It has been found that non-magnetic organic semiconducting materials can exhibit magnetic responses in electrical current, electroluminescence, photoluminescence, and photocurrent when an external magnetic field is applied. These intrinsic magnetic responses can be naturally attributed to (i) magnetic field-dependent singlet/triplet ratio and (ii) singlet/triplet ratio-dependent excited processes. We observe that inter-molecular and intra-molecular excited states are sensitive and insensitive, respectively, to external magnetic field in magnetic field dependences of electroluminescence, photocurrent, and photoluminescence. This experimental phenomenon suggests that the electron–hole separation distance essentially determines whether magnetic field effects can be activated through the competition between spin-exchange interaction-induced singlet–triplet energy difference and magnetic Zeeman splitting when applied magnetic field is stronger than spin–orbital coupling. Furthermore, the dissociation in inter-molecular excited states and exciton–charge reaction in intra-molecular excited states have positive and negative responses to external magnetic field. As a result, controlling the dissociation in inter-molecular excited states and the exciton–charge reaction in intra-molecular excited states provide an effective methodology to tune the magnetic field effects between positive and negative values in organic semiconducting materials.     

Synthesis and properties of starburst amorphous molecules: 1,3,5-Tris(1,8-naphthalimide-4-yl)benzenes

A series of starburst amorphous molecules derived from 1,3,5-tris(1-naphthyl)benzene are synthesized by a palladium-catalyzed Miyaura borylation and palladium-catalyzed Suzuki coupling reactions. These starburst compounds have the abilities to form uniform amorphous thin films and possess glass transition temperatures as high up to 254 °C. The high current density and luminance of organic light emitting diodes fabricated indicate that these compounds own good electron-transporting properties. These compounds hence have the potential to be used as electron-transporting materials in organic semiconducting devices.     

Multilayer encapsulation of plastic photovoltaic devices

We report the first results on conformal deposition of parylene on plastic solar cells, and study the effects of protection on performance characteristics of polymer solar cell. We show that single parylene coating layer is not a very effective barrier even for thicknesses as large as 10 μm. Our results support the experimental observations that the main degradation processes in poly(3-hexylthiophene) are the oxygen-assisted photochemical reactions, such as photobleaching and chain scission. Multilayer barriers made of parylene and aluminum oxide coatings are very promising for full protection of organic solar cell from degradation even under intense AM1.5 solar light.     

Role of the Bandgaps on Some Interfacial Phenomena with Ionocovalent Oxides

Many ionocovalent oxide materials are either semiconducting or insulating in nature.One of the most im-portant quantities characterising these materials,therefore,is the bandgap energy.The thermodynamic ap-proaches to the bandgaps of oxides are briefly described and some interracial phenomena with oxides are pres-ented.The standard electrode potentials of oxide electrodes and the heterogeneous catalytic behaviours of theoxides as well as the wetting and adhesion in liquid metal/oxide systems can be closely related to the bandgapenergies of the oxides.The interfacial phenomena involving the ionocovalent oxides are associated with theelectronic processes.     

Research progress in electron transport layer in perovskite solar cells

Since perovskite solar cells appeared in 2009, its simple preparation process, high photoelectric conversion efficiency and the characteristic of low cost in preparation process let it become the hot spot of both at-home and abroad. Owing to the constant efforts of scientists, the conversion efficiency of perovskite solar cells is more than 20% now. Perovskite solar cells are mainly composed of conductive glass, electron transport layer and hole transport layer, perovskite layer and electrode parts. This paper will briefly introduce the working principle and working process about the electron transport layer of perovskite solar cells. The paper focuses on aspects such as material types(e.g., inorganic electron transport materials, organic small molecule electron transport materials, surface modified electron transport materials and doped electron transport materials), preparation technology of electron transport layer, the effects of electron transport layer on the photovoltaic performance of the devices, and the electron transport layer in the future research.     

Progress in organic photocatalysts

Organic materials have advantages of diversity,ease of functionality, self-assembly, etc. The varied mechanistic pathways also make it conceivable to design an appropriate photocatalyst for an identical reaction. From this perspective, organic photocatalysts find wide applications in homogeneous, heterogeneous photocatalysis and photoelectrochemical(PEC) solar cells. In this review, the form of the employed organic photocatalysts ranging from molecules, supported molecules, to nanostructures or thinfilm aggregates will be firstly discussed. Rational design strategies relating to each form are also provided, aiming to enhance the photoenergy conversion efficiency. Finally,the ongoing directions for future improvement of organic materials in high-quality optoelectronic devices are also proposed.     

Semiconducting properties of thin films with embedded nanoparticles

We demonstrate here the possibility of designing semiconducting thin films with controlled electrochemical properties. The thin films are composed of (i) an insulating binder and (ii) a semiconductor nanopowder which enables the fine tuning of the semiconducting properties of the layers. Thus, p- and n-type silicon particles (obtained from a top-down technique), or metal-oxide ZnO, SnO2 and NiO nanoparticles (synthesized using a bottom-up protocol) are successfully integrated into spin-coated or screen-printed thin films and used as semiconducting materials. The flat band potential (Vfb) of the films is then easily tuned from 0 V to ?1.138 V.     

Double-walled carbon nanotube/polymer nanocomposites: Electrical properties under dc and ac fields

The electrical properties of the poly(methyl methacrylate:carbon nanotubes nanocomposites) have been investigated by direct current conductivity and complex impedance spectroscopy methods. The direct current conductivity results of the poly(methyl methacrylate):carbon nanotube as a nanocomposites show that the electrical conductivity property of the poly(methyl methacrylate) changes from insulating state to semiconducting state with incorporation of double wall carbon nanotube DWCNTs into insulating polymer matrix. The alternating current conductivity mechanism of the nanocomposites is controlled by the correlated barrier hopping mechanism. The correlated barrier hopping CBH model for intimate valence alternation pairs IVAP's describes the conduction mechanism of PMMA doped with (1%) DWCNTs, while correlated barrier hopping CBH model for non-intimate valence alternation pairs describes the conduction mechanism of PMMA doped with (5% and 8%) DWCNTs. The real part of the complex impedance decreases with the increase of the applied frequency which revealed that the PMMA:DWCNT nanocomposites behaves like semiconducting materials. The complex impedance Nyquist plots for PMMA doped with different concentration DWCNTs over are characterized by the appearance of a single semicircular arc whose radii of curvature decreases with increasing the temperature. Cole and Cole plots show the presence of temperature dependent electrical relaxation phenomena in the PMMA:DWCNT nanocomposites. The obtained electronic parameters confirm that PMMA:DWCNTs exhibit organic semiconductor behavior.     

Metal complexes of (LH2) ligand: 8,9-bis(hydroxyimino)-4,7,10,13-tetraaza-1,2,15,16-O-dicyclopentylidenehexadecane: Crystal structure,electrical and optical properties

Molecular semiconducting complexes constitute one of the most fascinating, recent research topics, deeply involving both chemists and solid states physicists. Considerable interest has been shown in the synthesis and study of molecular complexes which may behave like semiconducting materials or at least show high conductivities. In this study, structural, electrical and thermal conductivity and optical properties of some inorganic complexes were investigated. From the XRD data, the unit cells of the samples were found as L–Cu is amorphous and L–Ni, L–Co are orthorhombic. L–Cu, L–Ni and L–Co have n-type of electrical conductivity. Electrical and optical band gaps of the complexes were found to be 1.46–1.36, 2.68–2.71 and 1.40–1.32 eV, respectively.     

Using a molten organic conducting material to infiltrate a nanoporous semiconductor film and its use in solid-state dye-sensitized solar cells

We describe a method to fill thin films of nanoporous TiO₂ with solid organic hole-conducting materials and demonstrate the procedure specifically for use in the preparation of dye-sensitized solar cells. Cross-sections of the films were investigated by scanning electron microscopy and it was observed that a hot molten organic material fills pores that are 10 μm below the surface of the film. We characterized the incident photon to current conversion efficiency properties of the solid TiO₂/organic dye/organic hole-conductor heterojunctions and the spectra show that the dye is still active after the melting process.     

基于矿物特性的太阳能储热材料研究进展

相变材料因其优越潜热被广泛应用于太阳能光热技术中,绝大多数有机相变材料的导热系数非常低,大多介于0．1～0．4W·m^-1·K^-1之间。此外,相变材料流动性大,因此需采用导热性能好、具有稳定结构的基体支撑有机相变材料,改善其应用性能。一些天然矿物具有适当的比热与导热系数、多孔道的微结构以及天然的热稳定性与化学兼容性等矿物特性,被用于支撑相变材料制备太阳能储热材料。探讨了矿物的结构特性与性能优势,总结了石墨、珍珠岩、蛭石、硅藻土、埃洛石以及石膏等矿物基太阳能储热材料的制备研究。在此基础上介绍了矿物基太阳能储热材料在太阳能建筑节能、太阳能热水器、太阳能热发电等太阳能光热领域中的应用,并展望了矿物基太阳能储热材料的发展趋势和应用前景。     

Mikrobielle Werkstoffzerstörung – Simulation,Schadensfälle und Gegenmaßnahmen für anorganische nichtmetallische Werkstoffe: Biodeteriorationsprozesse an anorganischen Werkstoffen und mögliche Gegenmaßnahmen

Microbial deterioration of materials – simulation, case histories, and countermeasures for inorganic nonmetallic materials: Biodeterioration processes on inorganic materials and means of countermeasures Biodeterioration processes on inorganic materials such as natural stone, concrete, or glass can be subdivided into biogeochemical and biogeophysiological mechanisms according to their damage characteristics. In connection with the partial acidification and dissolving of components, biocorrosion as a result of biogenic release of inorganic and organic acids, as well as the biogenic oxidation of mineral forming cations, a certain weakening in the structure of the respective material can occur. The formation of biofilms on the surfaces of the inorganic materials impairs not only the aesthetical appearance of an object but also causes alterations in its humidity and temperature behaviour. In addition, due to the shrinking and swelling effects of biofilms, mechanical pressure to the mineral unit can occur (bioerosion, bioabrasion). Location and environmental factors which could lead to specific, biogenically determined weathering phenomena on these materials will be presented and elucidated. For controlling biodeterioration processes, the development and selection of environmentally-friendly, yet effective, inorganic and organic biocidal additives for stoneprotection agents as well as the use of gas (e.g. ethylene oxide) in their far-reaching significance for future material research will be presented here.     

Influences of dehydrating process on properties of ATO nano-powders

1　INTRODUCTIONCrystallineSbdopedtinoxide (ATO) ,cassiteritestructure ,isawidebandgapn typesemiconductor.Be causeofitsopticalproperty (transparentforvisiblelightandreflectiveforIR )andelectroconductibility ,goodchemicalandmechanicalstability ,ithasmanyapplica tions,suchastransparentconductiveelectrodes ,photo voltaicdevices ,photosensors ,catalyst,antistaticcoatingsandelectrochromicmaterials[14 ] .AvarietyoftechniqueshavebeenusedtoprepareATOsuperfinepowders ,someinvolvedryprocesses ,ot…     

On the electronic transport properties of pyrrolo[1,2-a][1,10]phenanthroline derivatives in thin films

The temperature dependences of electrical conductivity, σ, and Seebeck coefficient, S, for six new synthesized pyrrolo[1,2-a][1,10]phenanthroline compounds, have been investigated. Thin film samples (d = 0.05–0.66 μm) deposited by an immersion method (with dimethylformamide as solvent) onto glass were used.The crystalline structure of as-prepared organic films was investigated by XRD. The sample surface was examined by means of AFM and optical microscopy techniques.The ln σ = f(10³/T) and S = f(10³/T) experimental curves are quite typical for polycrystalline semiconducting materials. The examined organic compounds show a p-type electrical conduction. The activation energy of electrical conduction ranged between 1.42 and 2.04 eV, while the ratio of charge carrier mobilities was in the range 0.76–0.90.The study of optical absorption evidenced direct bandgaps ranged between 4.06 and 4.11 eV, as well bandgaps of 2.69–3.58 eV for amorphous phases.Some relationships between materials parameters and molecular structure of the compounds are established. The model based on band gap representation is suitable for the explanation of charge transport in the studied compounds.     

Charge transport properties of an organic solar cell

The electronic properties of ITO/PEDOT-PSS/P3HT-PCBM/LiF/Al organic solar cell have been investigated using current-voltage and capacitance-voltage techniques. The electrical parameters like ideality factor n, series resistance R_s and barrier height ?_b, have been extracted using current-voltage and capacitance-voltage techniques. The photovoltaic parameters such as open circuit voltage V_oc, short circuit current I_sc and fill factor FF were determined from current-voltage characteristics of the solar cell under illumination. The ideal value than unity for the organic solar cell indicates the presence of non-ideal behaviour. The barrier height of the solar cell is found to be dependent both temperature and applied voltage and the model of Gaussian distribution of the barrier height was presented for explaining their anomalous behaviour. The standard deviation of the barrier height distribution σ_o indicates the presence of interface inhomogeneities. The ideality factor n, open circuit voltage V_oc, short circuit current density J_sc, fill factor FF and Richardson constant A* values for the organic solar cell were found to be 2.29, 0.58 V, 5.84 mA/cm², 0.31 and 10.41 A/cm² K², respectively.     

Fundamental research needs in organic electronic materials

The workshop, Fundamental Research Needs in Organic Electronic Materials, jointly sponsored by DOE Basic Energy Sciences (BES) and EERE/BT was held on May 23–25, 2003 at the University of Utah Campus in Salt Lake City, Utah for the purpose of identifying key scientific issues enabling the technological success of these materials. Approximately 30 key experts and world leaders in organic materials chemistry, transport physics, time-resolved and steady-stated optical processes, organic spintronics, and device technology, gathered to stimulate new and revolutionary sciences.     

Possibility to Use Hydrothermally Synthesized CuFeS<Subscript>2</Subscript> Nanocomposite as an Acceptor in Hybrid Solar Cell

Here we have approached the plausible use of CuFeS₂ nanocomposite as an acceptor in organic–inorganic hybrid solar cell. To produce CuFeS₂ nanocomposite, hydrothermal strategy was employed. The room-temperature XRD pattern approves the synthesized material as CuFeS₂ with no phase impurity (JCPDS Card no: 37-0471). The elemental composition of the material was analyzed from the TEM-EDX data. The obtained selected area electron diffraction (SAED) planes harmonized with the XRD pattern of the synthesized product. Optical band gap (4.14 eV) of the composite from UV–Vis analysis depicts that the synthesized material is belonging to wide band gap semiconductor family. The HOMO (? 6.97 eV) and LUMO (? 2.93 eV) positions from electrochemical study reveal that there is a possibility of electron transfer from MEH-PPV to CuFeS₂. The optical absorption and photoluminescence spectra of MEH-PPV:CuFeS₂ (donor:acceptor) composite were recorded sequentially by varying weight ratios. The monotonic blue shifting of the absorption peak position indicated the interaction between donor and acceptor materials. The possibility of electron transfer from donor (MEH-PPV) to acceptor (CuFeS₂) was approved with photoluminescence analysis. Subsequently, we have fabricated a hybrid solar cell by incorporating CuFeS₂ nanocomposite with MEH-PPV in open atmosphere and obtained 0.3% power conversion efficiency.     

脉冲激光沉积及硒化法制备Cu(In,Ga)Se2薄膜研究

采用脉冲激光沉积和硒化后热处理的方法在石英衬底上制备Cu(In,Ga)Se2（简写为CIGS）薄膜,研究脉冲激光沉积（PLD）技术在制备CIGS薄膜太阳能电池材料上的应用,分析了不同预制层沉积顺序及厚度对CIGS薄膜组织结构、表面形貌、成分以及光学性能的影响。实验结果表明：(1)利用PLD技术及后硒化处理的工艺,制得的CIGS太阳能电池吸收层具有纯相和高结晶度等特性;(2)CuGa/In金属预制层的叠层顺序和叠层数、硒化退火温度对薄膜的结晶质量、晶粒尺寸、成分都具有重要的影响,其中叠层顺序影响最为明显;(3)样品均表现出对可见光区具有透射率低和吸收系数高的光学特性。本工作为制备性能优良的CIGS太阳能电池吸收层,提供了一个新颖的工艺手段。