Scientists have invented a way to view and create ‘an Electron Superhighway’ in an Organic Semiconductor

University of Vermont scientists have invented a new way to create what they are calling an electron superhighway in an organic semiconductor that promises to allow electrons to flow faster and farther — aiding the hunt for flexible electronics, organic solar cells, and other low-cost alternatives to silicon. To explore these organic materials, UVM graduate students (from left) Naveen Rawat and Lane Manning, and professors Randy Headrick and Madalina Furis, deployed this table-top scanning laser microscope. Their latest finding is reported in the journal Nature Communications — and may, someday not too far off, let you roll up your computer like a piece of paper. Credit: Joshua Brown, UVM

This approach promises to allow electrons to flow faster and farther – aiding the hunt for flexible electronics,organic solar cells, and other low-cost alternatives to silicon. TV screens that roll up. Roofing tiles that double as solar panels. Sun-powered cell phone chargers woven into the fabric of backpacks. A new generation of organic semiconductors may allow these kinds of flexible electronics to be manufactured at low cost, says University of Vermont physicist and materials scientist Madalina Furis.

Furis et al have created a low-cost blue dye called phthalocyanine – promising electrons to flow faster and farther in organic semiconductors. Many of these types of flexible electronic devices will rely on thin films of organic materials that catch sunlight and convert the light into electric current using excited states in the material called “excitons.” An exciton is a displaced electron bound together with the hole it left behind. Increasing the distance these excitons can diffuse – before they reach a juncture where they’re broken apart to produce electrical current – is essential to improving the efficiency of organic semiconductors.

Using a new imaging technique, the UVM team was able to observe nanoscale defects and boundaries in the crystal grains in the thin films of phthalocyanine – roadblocks in the electron highway. To find these defects, they built a scanning laser microscope, “as big as a table” Furis says. The instrument combines a specialized form of linearly polarized light and photoluminescence to optically probe the molecular structure of the phthalocyanine crystals.

The new technique allows the scientists a deeper understanding of how the arrangement of molecules and the boundaries in the crystals influence the movement of excitons. It’s these boundaries that form a “barrier for exciton diffusion,” the team writes. And then, with this enhanced view, “this energy barrier can be entirely eliminated,”. The trick: controlling how the thin films are deposited.

Though excitons are neutrally charged — and can’t be pushed by voltage like the electrons flowing in a light bulb — they can, in a sense, bounce from one of these tightly stacked molecules to the next. This allows organic thin films to carry energy along this molecular highway with relative ease, though no net electrical charge is transported. “One of today’s big challenges is how to make better photovoltaics and solar technologies,” says Furis, who directs UVM’s program in materials science, “and to do that we need a deeper understanding of exciton diffusion. That’s what this research is about.” http://www.uvm.edu/~uvmpr/?Page=news&storyID=21419