Molecules in blue jean and ink dyes could lead to better solar cells

Cornell University researchers have discovered a simple process employing molecules typically used in blue jean and ink dyes for building an organic framework that could pave way for economical, flexible and versatile solar cells.

Today's heavy silicon panels are effective, but they can also be expensive and unwieldy.

In a bid to searching for alternatives, William Dichtel and Eric L. Spitler, employed a strategy that 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.

"We had to develop a completely new way of making the materials in general," nature quoted Dichtel as saying.

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, but the correct structure is the most stable, so eventually, the more perfect structures end up dominating," said Dichtel.

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 porosity.

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

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. We're trying to remove as much of that element of luck as we can," said Dichtel.

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, said Dichtel.

The discovery is reported in the journal Nature Chemistry.