Electrically Controllable Spin States of Holes and Electrons in Organic Semiconductor Materials

Elucidating hole and electron states in organic semiconductor materials is one of the important issues for both their fundamental science and device applications. However, the detailed charge states, in particular, their spin states, have not yet been fully elucidated from a microscopic viewpoint. Here we show electrically controllable spin states of holes and electrons in typical organic semiconductor materials, a polymer regioregular poly(3-hexylthiophene) (RR-P3HT) and a small molecule pentacene, using electron spin resonance (ESR) spectroscopy. By use of their ambipolar organic semiconductor devices, these states were revealed as a function of accumulated charge density. The spin states of the electrically accumulated electrons in RR-P3HT and pentacene are clarified for the first time. Moreover, the formation of spinless states of electrons in RR-P3HT and holes in pentacene are demonstrated under high charge density, showing a contrast to the spin states under low charge density. This result would be important for further understating hole and electron states in organic semiconductor materials and for improving the performance of organic semiconductor devices from a microscopic viewpoint.