Stanford School of Engineering

Stanford engineers achieve record conductivity in strained lattice organic semiconductor

Using new technique researchers are able to pack molecules more closely than ever before to more than double the speed at which electrical charge can move through the semiconductor material

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

In a paper to be published online on Wednesday by the journal Nature, researchers at Stanford led by chemical engineer Zhenan Bao have changed that equation by improving the ability of the electrons to move through organic semiconductors. The secret is in packing the molecules closer together as the semiconductor crystals form, a technique engineers describe as straining the lattice.

Bao and her colleagues have more than doubled the record for electrical conductivity of an organic semiconductor and shown an eleven-fold improvement over unstrained lattices of the same semiconductor.

"Strained lattices are no secret. We've known about their favorable electrical properties for decades and they are in use in today's silicon computer chips, but no one has been successful in creating a stable strained lattice organic semiconductor with a very short distance between molecules, until now," said Bao.

In the past, engineers have tried to compress the lattices in these materials by synthetically growing the crystals under great pressure. "But, as soon as you release the pressure, the crystal just goes back to its natural, unstrained state," said Bao. "We've been able to stabilize these crystals in tighter formations than ever before."