Cell harvests near infrared spectrum, is expected to be put to use in hybrid designs

Traditional photovoltaic solar cells -- based on silicon or thin films -- tend to be relatively good at capturing the visible light spectrum, but they miss out on a great deal of the full spectrum of light striking the Earth.  Efforts to remedy to this loss have ranged from biomimicry to quantum dots.

I. First All-Carbon Cell Lands

Now researchers at Professor Michael Strano's materials lab at the Massachusetts Institute of Technology have devised a new type of solar cell that reclaims part of that lost spectrum -- the near infrared light that makes up 40 percent of the solar energy striking the Earth.

The cell is a highly unusual all-carbon design consisting of an almost laughably novel mix of Buckyball (C60) and nanotube carbon.  The cell relies on having very pure, single-walled nanotubes in one of the two possible configurations of the structurized carbon.

The new cell combines buckyballs [pictured] with carbon nanotubes.
[Image Source: Neatorama]

Describes Professor Strano, "This is the first all-carbon photovoltaic cell.  It has only been within the last few years or so that it has been possible to hand someone a vial of just one type of carbon nanotube."

Past groups have worked on nanotube cells as well, but their designs required polymer to stabilize the nanotubes and collect the electrons knocked off by incident light.  By contrast the new cell is all-carbon, yet appears relatively stable in air.

II. A Ways to Go

The cell is still very much in the proof-of-concept phase, with a lowly 0.1 percent conversion efficiency.  Still, Professor Strano imagines refined successor models being paired with traditional semiconductor/thin-film cells to form hybrid cells that offer more complete harvest of spectrum.

While the mixture of nanotubes is currently relatively pure, impurities are still having a major impact on efficiencies says lead author, graduate researcher Rishabh Jain.  He comments, "It's pretty clear to us the kinds of things that need to happen to increase the efficiency.  It’s very much a model system and other groups will help to increase the efficiency."

Michael Arnold, an assistant professor of materials science and engineering at the University of Wisconsin at Madison, acting as an independent commentator praises the work, stating, "Carbon nanotubes offer tantalizing possibilities for increasing the efficiency of solar cells and are kind of like photovoltaic polymers on steroids is exciting because it demonstrates photovoltaic power conversion using an active layer that is entirely made from carbon.  This seems like a very promising direction that will eventually allow for nanotubes’ promise to be more fully harnessed."

A layer of the researchers' mixed-carbon cell could one day be "painted" beneath a transparent thin-film cell.

An atomic micrograph of the novel carbon cell [Image Source: Rishabh Jain et al.]

Other reserachers involved in the study include graduate students Rachel Howden, Steven Shimizu and Andrew Hilmer; postdoc Thomas McNicholas; and professor of chemical engineering Karen Gleason.  The research was funded by the National Science Foundation (NSF), U.S. Department of Defense graduate fellowship grants, and a donation from Italian company Eni.

The work is published in the journal Advanced Materials. 

Source: MIT

"And boy have we patented it!" -- Steve Jobs, Macworld 2007

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