12 - Spintronics and magnetic field effects in organic semiconductors and devices

Abstract

Spintronics (also known as spin-based electronics) is an emerging technology that exploits the intrinsic spin transport of electrons other than their fundamental electronic charge. Organic semiconductors (OSCs) are composed of light elements that have weak spin-orbit interaction; consequently, they have long spin relaxation times, which makes them viable candidates for spin-transport materials in spintronics devices. Two types of organic spintronics devices have been extensively studied in the past few years: organic spin valves (OSVs) and organic light-emitting diodes (OLEDs), in which both conductivity and electroluminescence (EL) have been strongly modulated by an external magnetic field. In addition, optically detected magnetic resonance (ODMR) is an excellent complementary tool for investigating the electron-spin dynamics in OSCs. In this chapter, we describe the role of hyperfine interaction (HFI) in the spin response of films and devices based on conjugated polymers (CPs) made of protonated, H-hydrogen, deuterated, D-hydrogen, and 13C-rich chains. We experimentally prove that the HFI indeed plays a crucial role in all three spin responses. First, OLEDs based on the D-polymer show substantial narrower magneto-conductance (MC) and magneto-electroluminescence (MEL) responses. And the ultra-small MC and MEL responses at magnetic fields of few Gauss are also strongly isotope-dependent. Second, due to the longer obtained spin diffusion, OSV devices based on D-polymer show substantially larger magneto-resistance (MR) than devices based on H-polymers or C13-rich polymers. Films based on the D-polymer show considerably narrower polaron spin-half resonance than for H-polymers and C13-rich polymers. We also describe the time-resolved magneto-photoinduced absorption in π-conjugated copolymers in the time domain of picosecond to millisecond. Finally, our theoretical model describes these time-resolved magneto-photoinduced absorption results.