A review on organic spintronic materials and devices: II. Magnetoresistance in organic spin valves and spin organic light emitting diodes

In the preceding review paper, Paper I [Journal of Science: Advanced Materials and Devices 1 (2016) 128-140], we showed the major experimental and theoretical studies on the first organic spintronic subject, namely organic magnetoresistance (OMAR) in organic light emitting diodes (OLEDs). The topic has recently been of renewed interest as a result of a demonstration of the magneto-conductance (MC) that exceeds 1000% at room temperature using a certain type of organic compounds and device operating condition. In this report, we will review two additional organic spintronic devices, namely organic spin valves (OSVs) where only spin polarized holes exist to cause magnetoresistance (MR), and spin organic light emitting diodes (spin-OLEDs) where both spin polarized holes and electrons are injected into the organic emissive layer to form a magneto-electroluminescence (MEL) hysteretic loop. First, we outline the major advances in OSV studies for understanding the underlying physics of the spin transport mechanism in organic semiconductors (OSCs) and the spin injection/detection at the organic/ferromagnet interface (spinterface). We also highlight some of outstanding challenges in this promising research field. Second, the first successful demonstration of spin-OLEDs is reviewed. We also discuss challenges to achieve the high performance devices. Finally, we suggest an outlook on the future of organic spintronics by using organic single crystals and aligned polymers for the spin transport layer, and a self-assembled monolayer to achieve more controllability for the spinterface.