Twisting organic semiconductor crystals

Abstract

Crystals that twist as they grow are common but little known and introduce completely unexplored features to materials design. Here, we present growth-induced twists to molecular semiconductor crystals with the expectation that microstructure and continually precessing crystallographic orientations can modulate interactions with light, charge transport, and other optoelectronic processes. We have found that a variety of organic semiconductors and charge transfer complexes can be readily induced to grow from the melt as spherulites of tightly packed helicoidal fibrils. The twisting pitch can be controlled by the degree of undercooling after melting or through the incorporation of additives. Intriguingly, charge mobilities measured using field-effect transistor platforms have been found to increase with increasing extent of twisting. These results indicate crystal twisting to be a promising strategy for modulating the performance of optoelectronic devices.