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This top-down image shows the formation of the organic crystals as the semiconductor film dries. The film formation started at the top of the image and moved toward the bottom. (Image courtesy Gaurav Giri)

Organic semiconductors could usher in an era of foldable smart phones, better high-definition television screens and clothing made of materials that can harvest energy from the sun needed to charge your iPod or iPad, but there is one serious drawback: Organic semiconductors, while inexpensive, do not conduct electricity very well.

Yet this may soon change; by packing molecules closer together, Stanford scientists have developed improved organic semiconductor devices that are among the speediest yet. This new organic semiconductor—and the innovative process used to manufacture it—may significantly improve both the efficiency and cost of organic solar cells.

The secret of the new organic semiconductor is in packing the molecules closer together as the semiconductor crystals form, a technique engineers describe as straining the lattice. Using a technique similar to a coating process well known in industry, the Stanford team—led by graduate student Gaurav Giri of chemical engineering Professor Zhenan Bao's group—showed a six-fold improvement over unstrained lattices of the same semiconductor.

Bao’s team turned to SSRL staff scientist Stefan Mannsfeld and postdoctoral scholar Eric Verploegen to study the improved semiconductor to understand how and why it works so well. Experiments conducted at SSRL Beam Lines 7-2 and 11-3 revealed a remarkable, gradual distortion and strain in the molecular arrangement, making it possible to determine the how the molecules pack in the lattice and offering a better understanding of why such structures improve the molecule-to-molecule electrical coupling that enhances the electrical efficiency.

Stanford doctoral candidates Gaurav Giri, post-doctoral scholar Eric Verploegen, Ph.D., former post-doctoral scholar Hector Becerril, Ph.D., in Bao’s lab and Michael F. Toney, Ph.D., of the Stanford Synchrotron Radiation Lightsource Materials Sciences Division, contributed to this research.