General Electric Silicon Nano-Wire PV

General Electric is much better known for its utility grid products, its gas and steam turbines, and its nuclear reactors, than for its photovoltaic research. Yet it is General Electric that is announcing the potential for cheap, 18% efficient nanowire photovoltaics, from its ongoing research into silicon nanowires.

GE Global Research, the centralized research organization of the General Electric Company, announced that scientists on their Nano Photovoltaics (PV) team have demonstrated a scalable silicon nanowire-based solar cell, which has the potential to achieve up to 18% efficiency and be produced at a dramatically lower cost than conventional solar cells. This demonstration represents a promising development in the effort to make PV systems more economically viable for consumers.

GE reported its development recently in the journal Applied Physics Letters, which can be accessed online. The paper also was featured in the Virtual Journal of Nanoscale Science and Technology, which highlights the latest research in nanotechnology from various science journals. NextEnergy

Given General Electric's prominent position in the conventional power industry, its substantial investment in renewable energies should cause many investors and venture capitalists to pay even more attention than previously.

The cells were fabricated on a metal foil substrate, thus showing potential for future roll-to-roll manufacturing of such devices. We used standard, scaleable processes to grow the nanowires and to fabricate p-n junctions conformally around the nanowires. The use of conformal p-n junctions allows for de-coupling light absorption from charge transport. In a standard solar cell the active material must be thick enough to absorb all the sunlight (for silicon this is > 125 micrometers), however, as charge carriers diffuse back to the p-n junction many are lost due to non-radiative recombination. In these nanowire-based devices the minority carriers must only diffuse a few hundred nanometers to reach the charge-separating junction. The nanowire cells also showed the expected improvements in their optical properties. While the power conversion efficiency in these devices is still low, and much work remains to improve the performance, this nanoscale solar cell architecture and processing approach has promise to create a new paradigm in solar cell manufacturing and device design in the future. Source

GE has an ongoing collaboration with the U.S. Department of Energy (DOE) and is managing a three-year, $46.7 million project that is looking across the entire value chain to make solar energy more cost effective and more readily available in the marketplace. The program is evaluating three different technologies for the solar cell: high efficiency silicon-based cells, molded silicon wafers, and flexible thin films. DOE’s Solar America Initiative is designed to make solar energy cost-competitive with conventional forms of electricity by 2015. Of its own accord, GE has committed to more than doubling its level of investment in environmentally friendly technologies like solar from $700 million to $1.5 billion by the year 2010. GE is well on track to meet its commitment, surpassing the $1 billion mark in R+D spending this year.Gizmag

Other companies involved in nanowire PV include Cleanfield Alternative Energy Inc.

Brian Wang discusses more nanowire PV projects here.

Harvesting Waste Heat: Nanowire Thermoelectrics

Silicon nanowires offer us yet another way to turn waste heat from heat engines into electric power. Silicon is less expensive than previously used bismuth and tellurium.

The thermoelectric effect occurs when one end of a material, such as a wire, is heated. Electrons travel to the colder end, producing an electrical current. However, to harness this energy effectively it is critical that the temperature difference is maintained. This requires a material with an unusual combination of properties - excellent electrical conductivity but poor heat conductivity. As silicon conducts heat well, no-one was expecting it to be a good candidate.

...James Heath of the California Institute of Technology led one of the teams. 'It was a surprise,' he told Chemistry World. 'We found that when you make extremely small silicon nanowires there are some fundamental differences in how these materials behave and transfer heat.'...Heath believes that with further research the efficiency of these materials could be boosted even further. The technology could help to cool and power microchips in the future, he added.

...Francis DiSalvo has worked extensively on thermoelectric materials at the Cornell Fuel Cell Institute, Cornell University, New York. 'This research is exciting but there is still some way to go,' he told Chemistry World...One important role for thermoelectric materials would be capturing heat that is lost during energy production by power stations or car engines, DiSalvo said. 'If these materials can be made cheaply enough, capturing even a fraction of this wasted heat would make them worthwhile,' he added.

ChemistryWorld

One reason nanowires are able to perform better than bulk materials is that thermoelectric efficiency is dependent upon "ZT", the thermoelectric figure of merit. A ZT of 1 or greater provides a higher thermoelectric conversion efficiency. T is temperature, but Z = S**2σ/κ, where S is the Seebeck coefficient, sigma is the electrical conductivity, and kappa is the thermal conductivity. It was recently discovered that in nanowires, the ratio of electrical and thermal conductivities can be better controlled in the higher, more favourable direction.

“Bulk silicon is a poor thermoelectric material at room temperature, but by substantially reducing the thermal conductivity of our silicon nanowires without significantly reducing electrical conductivity, we have obtained ZT values of 0.60 at room temperatures in wires that were approximately 50 nanometers in diameter,” said Yang. “By reducing the diameter of the wires in combination with optimized doping and roughness control, we should be able to obtain ZT values of 1.0 or higher at room temperature.”

...When scaled up, thermoelectric modules could eventually be used in co-generating power with gas or steam turbines.

Source

By capturing an ever increasing percentage of waste heat, society is able to "turn back entropy" somewhat.

Now we simply need to develop ways of "turning back the entropy" that has taken hold in educational systems, political systems, and nihilistic religions and philosophies.


H/T Brian Wang

Phase Change Memory Using Nanowires

The quest to create fast, non-volatile phase-change memory dates to Stanford Ovshinky's 1966 patent application. Since then, many companies such as Intel, have made significant progress toward developing such a potentially revolutionary memory technology. The latest advance comes from a UPenn team that used nanowires to fabricate a phase change memory.

Ritesh Agarwal, an assistant professor in the Department of Materials Science and Engineering, and colleagues developed a self-assembling nanowire of germanium antimony telluride, a phase-changing material that switches between amorphous and crystalline structures, the key to read/write computer memory. Fabrication of the nanoscale devices, roughly 100 atoms in diameter, was performed without conventional lithography, the blunt, top-down manufacturing process that employs strong chemicals and often produces unusable materials with space, size and efficiency limitations.

Instead, researchers used self-assembly, a process by which chemical reactants crystallize at lower temperatures mediated by nanoscale metal catalysts to spontaneously form nanowires that were 30-50 nanometers in diameter and 10 micrometers in length, and then they fabricated memory devices on silicon substrates.

“We measured the resulting nanowires for write-current amplitude, switching speed between amorphous and crystalline phases, long-term durability and data retention time,” Agarwal said.

Tests showed extremely low power consumption for data encoding (0.7mW per bit). They also indicated the data writing, erasing and retrieval (50 nanoseconds) to be 1,000 times faster than conventional Flash memory and indicated the device would not lose data even after approximately 100,000 years of use, all with the potential to realize terabit-level nonvolatile memory device density.

“This new form of memory has the potential to revolutionize the way we share information, transfer data and even download entertainment as consumers,” Agarwal said. “This represents a potential sea-change in the way we access and store data.”

Eurekalert

The history of computer memory research is littered with failed concepts that offered great promise, but could not deliver for technical or economic reasons. Phase change memory technology is a relatively simple concept and should not be expensive, once developed. It will be much faster and more radiation resistant than flash memory, and will last much longer. Memory density should also be better than flash, and since it is non-volatile, it may become a replacement for hard disk drives. If it can be made fast enough, it may also replace volatile RAM memory.

In other words, regardless of whether phase change memory is implemented from the top down (lithography) or the bottom up (nano-wires), the underlying technology is likely to come standard, at least in top of the line machines, in the near future.

Hat tip Brian Wang.