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Ali Javey and Zhiyong Fan at Berkeley Lab have invented a method for growing highly regular, single-crystalline nanopillar arrays of optically active semiconductors to produce efficient, 3D solar cells. The 3D configuration allows for less stringent requirements in terms of the quality and purity of the input materials, providing for a reduction in cost compared to other solar cell configurations.
The Berkeley Lab invention uses a "vapor-liquid-solid" process that produces large-scale modules of dense, ordered arrays of nanopillars. Researchers tested their method by producing a solar cell composed of electron-rich CdS nanopillars embedded in a polycrystalline thin film of hole-rich CdTe. The efficiency of this prototype was 6%, which may be readily improved with concentrators, more transparent top contacts, and optimization of the nanopillar dimensions. The technology was also used to produce solar modules on flexible substrates that offer more efficient light absorption and carrier collection than rigid arrays. These flexible arrays could be bent repeatedly without damage or loss of cell performance.
The ability to deposit single-crystalline semiconductors on support substrates is crucial in the development of efficient photovoltaics. However, the process, usually performed with epitaxial crystal growth, has been expensive and inefficient. In addition, when amorphous substrates have been used to grow single-crystalline nanowires non-epitaxially, at less expense, the nanowires have varied in size, alignment, and density giving the resulting arrays a limited efficiency of approximately 0.5%. The Berkeley Lab technology offers a significant improvement in efficiency and manufacturability.
Xiaogan Liang of Berkeley Lab has invented an inexpensive, high-throughput process for depositing pure few-layer-graphene (FLG) in a desired pattern onto substrates, such as silicon wafers. This method uses electrostatic forces to print FLG in dimensions ranging from less than 20 nm to 100 μm and has the potential to be combined with step-and-repeat technology to cover large areas.
In the Berkeley Lab technology, the desired pattern is created on the pristine surface of a highly oriented pyrolytic graphite (HOPG) stamp. The stamp is brought into contact with the substrate, and one to three layers of graphene are deposited with great accuracy by the application of electrostatic forces. The stamp is removed and the graphene remains bonded to the substrate by van de Waals forces alone.
The invention was used to create 1.4 μm pillars and 18 nm-wide nanolines of FLG on SiO2/Si substrates. These structures were visualized with scanning electron microscopy and atomic force microscopy, and their graphene composition was confirmed with Raman spectroscopy. The nanolines were used to create transistors that had excellent transport properties with highly mobile holes and electrons. The rapid current in the FLG nanolines and nanoribbons and their high sensitivity to electric fields may also allow for applications in biosensors, antennae, and photovoltaics.
Graphene offers significant advantages over silicon as a potential semiconductor because of its exceptional electronic properties: high carrier mobility, stable 2D structure, and the potential to enable scatter-free electron movement at room temperature. However, several obstacles have prevented graphene from being used for commercial electronics. Primarily, it is difficult to deposit graphene in a precise and electronically useful pattern over the relatively large (6 in., 8 in., or 12 in.) surface of a standard silicon wafer or other substrate. Current methods such as epitaxial growth, adhesive application, and reactive deposition are either expensive or risk contamination of the deposited material. The Berkeley Lab technology overcomes these limitations to make graphene a viable semiconductor material.
Researchers at Berkeley Lab have developed a highly efficient technology for the reclamation of waste heat in mechanical heat engines widely used in solar-thermal, geothermal, and industrial processes. This new approach yields gains in efficiencies for both high temperature and intermediate temperature thermal sources, marking a significant advance over strategies that focus predominately on high temperature efficiency solutions.
The Berkeley Lab energy reclamation technology uses an Organic Flash Cycle (OFC) that increases exergetic efficiency with isentropic or "dry" aromatic hydrocarbons as working fluids that almost perfectly match the temperature of the thermal resource, reducing a major contributor of system energy conversion inefficiencies. Heat addition takes place completely in the liquid phase of the cycle with the working fluid vaporized during flash evaporation.
The OFC invention has several configurations, each suited to different conditions and cycle requirements. For high temperature applications between approximately 200ºC and 400ºC, the single flash OFC achieves efficiencies comparable to the optimized Organic Rankine Cycle (ORC), but uses a simpler configuration. For lower temperature thermal resources in the range of approximately 80ºC to 150ºC, a secondary flash stop vaporizes more fluid for additional reclamation gains.
Another variation on the basic OFC replaces the throttling valve with a more efficient two-phase expander to reduce system irreversibility. The OFC outperforms the basic ORC with approximately 20% to 50% greater thermal energy utilization. It has approximately 90% heat addition efficiency compared to about 70% for basic ORC, about 75% for a zeotropic Rankine cycle with a binary ammonia-water mixture, and about 80% for a CO2 transcritical cycle.
Current cycle technologies for reclaiming waste heat are extensively used in traditional manufacturing industries including petroleum refining, pulp and paper, iron and steel, food and beverages, cement, fabricated metals. The implementation of OFC in these industries has the potential of an annual recovery of up to 1,703 quadrillion BTUs from waste heat with an approximate savings of $5.8 billion per year. The OFC is also a promising reclamation strategy for renewable energy sources such as solar thermal, geothermal, and biomass.
Researchers at the Joint BioEnergy Institute (JBEI) have developed a hyperthermophilic cellobiohydrolase protein (CBH) to break down cellulose into cellobiose at high temperatures. The JBEI CBH can be used in concert with JBEI endoglucanases (or any other endoglucanase with a similar temperature and ph profile) in high concentrations of ionic liquid. There is no loss of activity in ionic liquid concentrations up to 20%, and the enzyme cocktail is tolerant of ionic liquid concentrations of up to 50%. Therefore, the JBEI technology opens the possibility of one pot saccharification of lignocellulosic biomass. In addition, the JBEI technology is compatible, theoretically, with other pretreatment methods such as dilute acid and ammonia fiber explosion.
The JBEI CBH, isolated from Caldicellulosiruptor saccarolyticus, shows high CBH activity against insoluble substrates and has a higher tolerance to ionic liquid than a commercial enzyme cocktail developed for enzymatic hydrolysis of biomass. The enzyme retained more than 75% of the original activity over four days of incubation at 70ºC. Further, the technology functions at high temperatures (up to 80ºC), thus reducing the risk of contamination by other microorganisms
Current techniques treat biomass with a combination of high temperatures and an acid or base, or chemicals such as lime. One disadvantage of this method is that the industrial enzymes used to break down cellulose are not compatible with such harsh treatments. Therefore, single pot pretreatment/saccharification is impossible. In addition, current approaches create unwanted byproducts that interfere with the downstream hydrolysis and fermentation and do not lead to complete hydrolysis of the cellulose to sugars.
Ionic liquids have been shown to be effective in fully solubilizing lignocellulosic biomass. However, the addition of anti-solvents to separate the solubilized components of biomass (cellulose, hemicellulose and lignin) is an expensive and time consuming step. This new JBEI technology eliminates this step and maximizes hydrolysis.
EIO-2745 is compatible with JBEI invention EJIB-2666, Thermophilic Cellulases Compatible with Ionic Liquid Pretreatment.
Multiwall nanotubes of carbon (CNT) and of boron nitride (BNNT) have a very high thermal conductance at room temperature. Their twin properties of high thermal conductivity along the axial direction and poor thermal conductivity in the radial direction provide an excellent heat conduction channel that can confine heat currents on the nano scale.
Alex Zettl and Chih-wei Chang of Lawrence Berkeley National Laboratory have determined that CNT and BNNT are also highly efficient under conditions of severe mechanical deformation (at angles of more than 130 degrees). This means that they can function not only as sensitive nanoelectromechanical devices but also as robust broadband phonon waveguides conducting heat through phonons, or quantized soundwaves, around corners. In addition to their use in thermal links, their light weight, stiffness, and tensile strength (50 times greater than steel) show promise for flexible electronics and composites subject to mechanical strain.
Nanotubes may also be used as synthetic acoustic bandgap (ABG) materials, making it possible to control the propagation and distribution of acoustic waves or phonons. ABGs on this scale can provide acoustic isolation of microfabricated devices such as radio frequency resonators and sensors, and miniature acoustic waveguides can be used for ultrasound and signal processing. As ABGs are produced at smaller sizes operating at higher frequencies, applications in thermal management and engineering the thermal noise distribution of a material become feasible. Defected acoustic crystals can potentially be used as “mirrors” for micro-cavities, providing higher frequency selectivity than competing technologies.
While phonon transmission is only minimally affected by deformation, electron transmission is more significantly affected. Coupling the two allows phonon signals to be used to carry information.
An approach developed by Robert Kostecki and Marek Marcinek of Berkeley Lab has given rise to a new generation of nanostructured carbon-tin films that can be produced quickly, efficiently, and inexpensively. These binderless carbon/tin thin-film anodes provide enhanced charge capacity and excellent cycleability in lithium ion battery systems compared with lithium ion anodes currently on the market.
Berkeley Lab’s method uses microwave plasma chemical vapor deposition to fabricate nanostructured carbon/tin composite films in a convenient one step synthesis process. The porous 3D architecture of the carbon/tin films is mechanically stable and offers maximum electronic contact between the tin and the carbon. Nanoparticles of tin are uniformly dispersed and fully embedded in a carbon matrix. The resulting nanocomposite accommodates volumetric changes of tin upon charge-discharge processes and exhibits exceptional electrochemical durability.
These high capacity carbon/tin films can be grown directly on any type of substrate from organic precursors in a vacuum chamber. The film deposition process can be easily adapted to reel-to-reel fabrication processes that are in common use in the industry. This technology can also find applications in the fuel cell industry (e.g., carbon/platinum composites) as well as the semiconductor and coating industries.
Mark Modera and Francois Remi Carrie from Berkeley National Laboratory have developed a rapid, economical technique to seal duct and other enclosed systems by means of an internally injected aerosol.
Berkeley National Laboratory's aerosol compound seals holes in enclosed systems and is effective even after bends and junctions. A unique, in situ aerosol sealing apparatus, also designed and built at Berkeley National Laboratory, delivers the new sealing aerosol. This multifunctional field apparatus, designed to be portable and easy to use, is powered by two, household circuits (15A/110V) and does not require the use of desiccants. In addition to performing the sealing process, Berkeley National Laboratory's compact field apparatus also measures leakage of the system before and after sealing, eliminating the need to invest in and field additional equipment. A description of the clog-free atomizing and spray drying nozzle specially designed for use with this technology is referenced below.
Robert Cheng at Berkeley National Laboratory has developed a means for retrofitting existing burners to burn lean, premixed natural gas/air mixtures to reduce NOx emissions without sacrificing efficiency and burner design simplicity.
New burner designs can also incorporate the basic principle of this device. This technology answers the needs of meeting clean air standards by application of a simple and economic method to reduce the emission of pollutants. This Berkeley National Laboratory device is best suited for small- to medium-sized water heaters and forced-air furnaces.
John Kerr and co-workers at Berkeley Lab have developed single-ion cross-linked comb-branched polymer electrolytes with high conductivity for use as membranes in lithium batteries, fuel cells, and electrochromic windows. Solid polymer electrolyte separators are used in lithium batteries instead of common organic solvents because (1) they are non-volatile, (2) they inhibit the growth of dendrites, the tiny metallic snowflake structures in lithium metal electrodes that lead to battery failure, and (3) they can be used in very thin films thereby improving the power performance of the battery and increasing the energy density.
Solid polymer electrolytes have been improved by the creation of single-ion polymer conductors. Single ion conductors, transference number of one, avoid the development of concentration gradients that result in low voltage upon discharge and irreparable damage on charge because the anion is immobilized by covalently connecting it to the polymer comb. Until now, lithium single ion polymer conductors have been plagued with low conductivity, reactivity to lithium, poor cathode compatibility, and mechanical stiffness that leads to poor processing properties. Kerr’s new cross-linked polymer electrolytes based on trifluoromethylsulfonylmethide, sulfonate, and fluoroalkylsulfonate and imide anions overcome these limitations.
The controllable method of preparation results in a material that has uniformly excellent mechanical and ion transport properties that appear to be unaffected by the cross-linking density. This allows density to be varied to suit the application. The cross-linked materials achieve much higher lithium ion conductivities than other cross-linked polymers (10-5 S/cm at ambient temperatures) and yet also inhibit dendrite growth due to the mechanical properties. The side chains of the comb-branched structures are long enough to allow for maximum segmental motion so that the polymer can effectively penetrate between the electrode particles and adhere to electrode surfaces while maintaining the amorphous nature that facilitates high ion mobility. This overcomes many of the problems involved in the preparation of good composite electrode structures.
The capabilities, materials, and principles used for developing these polymer electrolytes for lithium batteries can be adapted to develop polymer films for fuel cells and electrochromic windows. Kerr’s group is investigating the use of new proton solvating functions on comb branch polyether polyelectrolyte materials to provide water-free membranes that can operate at high temperatures for fuel cells.
Berkeley Lab researchers Mike Tucker, Grace Lau, and Craig Jacobson have invented a novel layered structure for preparing a high-operating temperature electrochemical cell.
The structural support is porous metal, an unconventional approach which imparts strength, while use of the more expensive ceramic and cermet materials is confined to the thin active layers. Due to several unique processing techniques, a wider range of catalysts can be introduced into the structure than current methods allow. The Berkeley Lab process renders a robust, well-bonded electrochemical device that could be manufactured at significantly reduced cost.
Arlon Hunt and Samuel Mao and colleagues at Berkeley Lab have developed a new class of hydrogen and carbon dioxide (CO2) storage materials with favorable storage capacities under conditions suitable for on-board vehicle use.
The inventors are the first to use an oxide aerogel medium as the basic nanostructured framework for solid-based hydrogen and CO2 storage and capture. The highly porous medium is subjected to vapor infiltration with metal hydride or carbon to form a linked three-dimensional network of nanostructures.
The new Berkeley Lab materials take advantage of the high formula storage capacities of metal hydrides, for example, while overcoming their slow sorption kinetics and the need for high temperature desorption by incorporating the hydrides into an nanostructured template.
"Third-generation" PV technologies are being actively pursued in academic research labs. These include nano-optics, multi-junction architectures, multi-exciton, plasmonics, and lower cost tandem cells. The goal is a module cost of less than $0.60/watt. Many of these technologies are in exploratory or early research stages but still can be evaluated according to their material requirements, processing complexity, and potential scalability. For example, concepts that utilize GaAs or CIGS may have cost issues or material availability issues. Similarly, complex cell designs or designs that feature nano-architectures such as quantum wires may not be easily scaled.
Robert Kostecki and Sam Mao of Berkeley Lab have invented a new approach to affordable, third generation PV. The technology builds upon previous research that uses surface chemical reactions to generate and inject hot electrons into a metal catalyst. In the recent invention, light is absorbed by the PV material and hot electrons are generated. Charges are then separated across a Schottky barrier.
The technology is a simple, low cost, scalable solution that addresses the concerns of high cost materials, materials availability and toxicity, complexity of cell design, and large-scale manufacturability. It relies on cheap, abundant materials that do not require ultra-high purity processing. Various existing deposition technologies can be used for cell manufacturing, none of which rely on ultra-high vacuum or expensive MOCVD/MBE equipment. Based on the initial laboratory conceptual demonstration, greater than 10% efficiency is projected with process development on existing tool sets. The technology uses a simple cell design that, together with the processing flexibility, should provide a path to scalable manufacturing.