In this 21st Century Chemist profile, Iowa State University organic chemist Malika Jeffries-EL explains her work to make less costly, more energy-efficient semiconductors and LEDs from organic, carbon-based materials such as plastics, "doping" the organic materials so that they are more conductive.
From Metal to Plastic: Iowa State Chemist Works on Organic Semiconductors
TOM COSTELLO, reporting: From teaching, to mentoring, to collaborating. Malika Jeffries-El, assistant professor of chemistry at Iowa State University, knows how to bring out the best in her students and the materials they create.
MALIKA JEFFRIES-EL (Iowa State University): My laboratory is the plastic electronics laboratory. Our research interests are in the synthesis or developing of new materials for use as organic semiconductors.
COSTELLO: Semiconductors are materials that can conduct an electrical charge. The most common are made from metalloids, such as silicon, and are critical for powering cell phones, computers, most of today’s electronic devices. Jeffries-El is hoping to replace metalloid semiconductors with cheaper more efficient ones made from organic, carbon-based materials, like plastics.
JEFFRIES-EL: Plastics have just had such an impact on every day life. Our televisions are lighter, our phones are smaller and they can do more. Our computers are lighter and plastic was a key part in the outside, the things you do see, and now are starting to become a key part of the components inside that you do not see.
COSTELLO: The problem with carbon-based or plastic semiconductors is that these substances don't conduct electricity well. Jeffries-El is trying to improve their conductivity by altering the charges in the organic substance, a process she calls doping.
JEFFRIES-EL: You have to have a flow of positive and negative charges for there to be current. Semiconductors are materials that can do this. They don't tend to do well in their native states but usually if we dope it or seed them by introducing some carriers, then they will begin to transport.
COSTELLO: To visualize this, imagine a series of atoms placed in a crystalline pattern. For an electrical current to flow through the grid there needs to be a constant stream of electrons moving through it. In a metal conductor, electrons are able to move freely, but in semiconductors they are locked in a fixed position, they need help moving. By n-doping - replacing an atom with one that has extra electrons - or p-doping - replacing an atom with one that has less electrons, so-called holes - the extra electrons or holes are now free to move around from atom to atom, allowing greater conductivity.
JEFFRIES-EL: Some things conduct, some things don't and some things can't. They don't initially but they can. While our materials would not conduct the electricity on their own but if we seed them with dopents, they will.
COSTELLO: One of the organic semiconductors Jeffries-El is working to improve is something called O-LEDs – or Organic Light Emitting Diodes. O-LEDs provide the three key color components - red, green and blue - inside many flat screen TV's. Jeffries-El is focused on making a better blue.
JEFFRIES-EL: The biggest issue is stability and lifetime. Many of the blue materials tend to have shorter lifetimes than some of the other colors and so if your blue fails first, your whole TV may as well fail. So we need to try to make materials that can emit blue that are better in terms of their overall stability to some of the known reds and greens so we can increase the overall lifetime of the device.
COSTELLO: To create her organic light emitting diodes, Malika takes her polymers to the physics lab next door. There her polymers are built onto little slides and tested to find out how much light and what wavelength of light they emit, which determines their color.
JEFFRIES-EL: It's a real team effort. We're a little bit limited on what we can do. So now if we take it over the physics lab, with their set up, they actually fabricate the organic light emitting diode and the things that can characterize it. They can tell me which is more blue than the other and they can look at properties such as which one is the most efficient.
COSTELLO: A semiconductor that is more efficient and cheaper to make could do more than just improve flat-screen TV’s. They could also increase energy conservation around the world.
JEFFRIES-EL: The O-LEDs also tie in, because they are a very efficient source of lighting. Our ultimate goal is to make materials that would work for highly efficient solar cells. That’s our ultimate goal.
COSTELLO: Big ideas for some major problems. For Jeffries-El and her students, such inspiration can be found in tiny places.
JEFFRIES-EL: Nothing to me is more satisfying than when you're holding that flask with that vial and you know this is the molecule that you dreamt of and sketched out on a piece of paper, talked about it with the students. And a month later you're holding it in your hand. That is the most fulfilling part to me. It's like we dreamt it and we did it.
A solar cell is a device designed to change sunlight into electric power. Solar cells may be small, such as those used to power handheld calculators, or they may be combined to create larger panels, such as those that supply electricity for homes, businesses or even space stations.
Semiconductor, Plastic, Polymer, Carbon-Based, LEDs, Light-Emitting Diode, Organic, OLEDs, Conductive, Conductivity, Electricity, Current, Electrical, Dopent, Doping, P-Doping, N-Doping, Electrons, Malika Jeffries-EL, Iowa State University, Plastic Electronics Laboratory, Flat Screen TV, Color, Energy, Conservation, Energy-Efficient, Solar Cell, Lighting, Synthesis, Synthetic, Materials, National Science Foundation, 21st Century Chemist, "Chemistry Now", Laboratory, Chemistry, Organic Chemistry