[FPSPACE] Fw: Cornell Chronicle: New atomic framework could lead to better solarcells

LARRY KLAES ljk4 at msn.com
Thu Jul 1 17:25:07 EDT 2010

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From: Cornell Chronicle <cunews at cornell.edu>
Date: Thu, 1 Jul 2010 21:23:28 
To: <CUNEWS-SCIENCE-L at cornell.edu>; <CUNEWS-ENVIRONMENT-L at cornell.edu>; <CUNEWS-PHYSICAL_SCIENCE-L at cornell.edu>
Subject: Cornell Chronicle: New atomic framework could lead to better solar

Chronicle Online e-News

New molecular framework could lead to more efficient, flexible solar 

June 29, 2010

By Lauren Gold
LG34 at cornell.edu

Think of solar cells, and you probably imagine the thick, heavy silicon 
panels on rooftops in sunny climates.

Those panels are effective, but they can also be expensive and 
unwieldy. In the search for a better alternative, a team led by William 
Dichtel, assistant professor of chemistry and chemical biology, has 
discovered a simple process for building an organic molecular framework 
that could pave the way for the development of more economical, 
flexible and versatile solar cells.

The discovery is reported in an article published online on June 20 by 
the journal Nature Chemistry.

Dichtel's strategy uses organic dye molecules assembled into a 
structure known as a covalent organic framework (COF). Organic 
materials have long been recognized as having potential to create thin, 
flexible and low-cost photovoltaic devices, but it has been proven 
difficult to organize their component molecules reliably into ordered 
structures likely to maximize device performance.

COFs, a class of materials first reported in 2005, offer a new way to 
address this long-range ordering problem; but until now, the known 
methods for creating them had significant limitations.

"We had to develop a completely new way of making the materials in 
general," Dichtel said. The strategy uses a simple acid catalyst and 
relatively stable molecules called protected catechols to assemble key 
organic molecules into a neatly ordered two-dimensional sheet. These 
sheets stack on top of one another to form a lattice that provides 
pathways for charge to move through the material.

The reaction is also reversible, allowing for errors in the process to 
be undone and corrected.

"The whole system is constantly forming wrong structures alongside the 
correct one," Dichtel said, "but the correct structure is the most 
stable, so eventually, the more perfect structures end up dominating." 
The result is a structure with high surface area that maintains its 
precise and predictable molecular ordering over large areas.

The researchers used X-ray diffraction to confirm the material's 
molecular structure and surface area measurements to determine its 

At the core of the framework are molecules called phthalocyanines, a 
class of common industrial dyes used in products from blue jeans to ink 

Phthalocyanines are also closely related in structure to chlorophyll, 
the compound in plants that absorbs sunlight for photosynthesis. The 
compounds absorb almost the entire solar spectrum -- a rare property 
for a single organic material.

"For most organic materials used for electronics, there's a combination 
of some design to get the materials to perform well enough, and there's 
a little bit of an element of luck," Dichtel said. "We're trying to 
remove as much of that element of luck as we can."

The structure by itself is not a solar cell yet, but it is a model that 
will significantly broaden the scope of materials that can be used in 
COFs, Dichtel said. "We also hope to take advantage of their structural 
precision to answer fundamental scientific questions about moving 
electrons through organic materials."

Once the framework is assembled, the pores between the molecular 
latticework could potentially be filled with another organic material 
to form a light, flexible, highly efficient and easy-to-manufacture 
solar cell.

The next step is to begin testing ways of filling in the gaps with 
complementary molecules. "This is the very beginning of our work," he 

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