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Semiconductors are materials that are used as switches in modern electronics. While the switches in your computer and smartphone are made of silicon, carbon-based organic semiconductors offer the potential for flexible, inexpensive electronics. Toward this goal, students in CHEM 100R have synthesized a novel organic semiconductor. For an organic semiconductor film to perform well, it must be processed so that is both crystalline and continuous. Students in CHEM 165 explored three different methods, shown in these images, in an attempt to optimize the film. The first image shows a film that was spun coat onto a silicon wafer from a chloroform solution, then annealed causing the formation of discontinuous “islands.” The second image reveals crystals that were formed during drop casting from an acetone solution. Each of these long, ribbon-like crystals is like a separate, miniature highway that current can flow through. The third image shows microcrystals present in a film that was spun coat from a toluene solution. These connected microcrystals are akin to “back roads” that current can take through the film. Promising materials and methods like those seen here are continuing to be developed in the Advanced Undergraduate Laboratories at Harvard.

Contributed by undergraduate students in the Chemistry 165 class at Harvard University.

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