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Nanoelectronics November 2016 Viewpoints

Technology Analyst: Nick Evans

Thermophotovoltaics: Pushing the Envelope of Solar Power

By Alastair Cunningham
Cunningham is an independent consultant specializing in nanomaterials and electronics.

Why is this topic significant?

Standard photovoltaic technology is fast approaching its fundamental physical limitations. Recent research into next-generation techniques demonstrates how overcoming these limitations could be achievable.

Description

Researchers at the Massachusetts Institute of Technology (MIT) recently published the results of their research into next-generation photovoltaic devices that could dramatically increase the efficiency of solar-energy generation. The devices use the principles of thermophotovoltaics—essentially turning sunlight into heat energy before reemitting it as light that is more suitable for the photovoltaic component of the cell. The scientists achieve this reemission by adding a layer of vertically aligned carbon nanotubes—extremely efficient absorbers of light across the entire visible spectrum—at the surface of the photovoltaic cell. This layer also contains an array of nanoscale photonic crystals that can reemit the heat generated by the nanotubes at the specific wavelengths that the photovoltaic cell can most efficiently transform to electricity.

The researchers—for the first time—were able to demonstrate a thermophotovoltaic cell that exhibits a higher efficiency than that of the underlying photovoltaic cell. At 6.8%, the efficiency of the prototype thermophotovoltaic device was relatively low—standard silicon photovoltaics can achieve efficiencies of between approximately 32% and 40%. However, the scientists claim that further research could result in additional gains.

Implications

Blocking sunlight from arriving at the surface of a photovoltaic cell in order to improve its efficiency may appear counterintuitive. However, thermophotovoltaics has the potential to reshape the solar-power industry and, by extension, the entire market for renewable energy. Any advance that significantly improves on existing technology could cause a shift in industry standards and prove to be highly lucrative for early adopters.

Perhaps one of the most significant implications of this technology arises from the ability to store and transport heat easily. Stored heat could find use in the generation of photovoltaic power at all times, completely removing the need for direct sunlight and simultaneously solving problems relating to energy storage and the intermittent nature of generating power by means of standard solar technology.

However, despite the promise, this technology is in the early phases of its developmental cycle. Significant levels of additional research—focusing primarily on issues related to scale and manufacturing—will be necessary before thermophotovoltaics is in a position to challenge existing methods of power generation.

Impacts/Disruptions

Several other methods of improving photovoltaic devices are currently in development. For example, stacking solar cells on top of one another in order to maximize the power output is one technique that can find use in overcoming the fundamental limitations of the technology. Alternative approaches within the field of thermophotovoltaics also exist. Researchers at the Australian National University and the University of California, Berkeley, are researching the use of nanoscale metamaterials that would function in a manner similar to that of the MIT research. Ultimately, efficiency and cost will determine which, if any, of these emerging technologies will become a commercial success.

If thermophotovoltaic technology does prove to be a commercial success, then it could potentially also find use in harvesting other sources of waste heat such as industrial processes or the heat generated by an automotive engine. The nanoscale nature of this technology also lends itself particularly well to the wide range of flexible photovoltaics applications that are set to proliferate in the coming five years.

Scale of Impact

  • Low
  • Medium
  • High
The scale of impact for this topic is: High

Time of Impact

  • Now
  • 5 Years
  • 10 Years
  • 15 Years
The time of impact for this topic is: 10 Years to 15 Years

Opportunities in the following industry areas:

Photovoltaics, energy, renewables

Relevant to the following Explorer Technology Areas:

Commercialization of Carbon-Nanotube-Memory Technology

By Alastair Cunningham
Cunningham is an independent consultant specializing in nanomaterials and electronics.

Why is this topic significant?

Despite their impressive material properties, carbon nanotubes find no use in a wide variety of electronics applications. Recent developments describe a major breakthrough for the commercialization of the material in a novel memory technology.

Description

In August 2016, Fujitsu Semiconductor announced its licensing of Nantero's carbon-nanotube- (CNT-) based nonvolatile random-access-memory (NRAM) technology and its plans to bring a 256-gigabyte, 55-nanometer product to market within the next two years. Fujitsu Semiconductor will become the first manufacturer to mass-produce this technology, which, it claims, "achieves several 1000 times faster rewrites and many thousands of times more rewrite cycles than embedded flash memory." According to the press release, Fujitsu intends to develop a custom NRAM-embedded product in 2018, before expanding the product lineup into stand-alone NRAM devices. Mie Fujitsu—Fujitsu's pure-play foundry partner—will offer the product to its customers—who, in turn, will have the opportunity to rebrand and resell.

Nantero's NRAM technology is relatively easy to fabricate, exhibits high endurance (maintaining performance after 10 trillion cycles), and is stable at high temperatures (successfully functioning at temperatures of up to 200°C and retaining stored data at temperatures of up to 300°C for as long as ten years). The planar nature of NRAM limits its overall density. However, Nantero has a three-dimensional multilayer architecture in development that would significantly increase the density of the devices.

Implications

The involvement of Fujitsu Semiconductor—which has considerable experience in the development of nonvolatile RAM devices as well as integrated design and production capabilities—is likely to accelerate the commercialization of NRAM devices. Any such commercialization could prove to be particularly lucrative for Nantero, which invested in the development of the technology over a period of about a decade.

Reports suggest that Nantero is also working with six other fabrication plants and that some are working on 28-nanometer architectures that would significantly outperform the Fujitsu Semiconductor product. Nantero's model of licensing its intellectual property to several customers could also help to ensure the commercial success of NRAM over competing technologies.

Chief among these competing technologies is currently Intel and Micron's 3D XPoint, which "Phase Change Memory Developments" in the September 2016 Viewpoints discusses in greater detail. 3D XPoint is more commercially mature, which means that NRAM is unlikely to challenge seriously in the short term. However NRAM possesses a price advantage that could result in longer-term success.

Impacts/Disruptions

If commercially successful, NRAM would be likely to find use initially in server applications. The tolerance for high temperatures also means that the technology lends itself to extreme applications in, for example, the oil-and-gas industry. Indeed, Schlumberger—one of the world's leading suppliers of gas-and-oil exploration technology—is a "major strategic investor" in Nantero.

More broadly, the commercialization of an advanced CNT product represents a significant breakthrough for the nanoelectronics industry. Other advances in CNT technology also have the potential to have a major impact on the electronics industry. In addition to making advances in the CNT-based transparent conductive films that are already on the market, researchers are also making advances in the field of CNT transistors. For example, in September 2016, scientists at the University of Wisconsin-Madison announced that they can now fabricate prototype CNT transistors that outperform state-of-the-art silicon equivalents.

Scale of Impact

  • Low
  • Medium
  • High
The scale of impact for this topic is: High

Time of Impact

  • Now
  • 5 Years
  • 10 Years
  • 15 Years
The time of impact for this topic is: Now to 5 Years

Opportunities in the following industry areas:

Memory, integrated circuit, consumer electronics, oil and gas

Relevant to the following Explorer Technology Areas: