Room-temperature stable organic spin valves using solution-processed ambipolar naphthalenediimide-based conjugated polymers

Abstract During the past years, charge transport performance of solution-processed donor-acceptor (D-A) conjugated polymers has been explosively studied for successful instance of record-breaking carrier mobility. By contrast, corresponding spin dynamics was far-less probed except handful pioneering reports. Herein, we successfully observed room-temperature stable magnetoresistance (MR) response in organic spin valves using ambipolar naphthalenediimide-based D-A type conjugated polymers. Additionally, we found spin transport performance of these polymer-inserted junction was sensitive to chemical structures of polymer repeating units. Both alkyl-chain extension in the acceptor unit and cyano-group substitution in the donor unit can induce evident MR drop. Furthermore, we discovered spin dynamics inside these ambipolar materials exhibited disparate electrical dependence from classical unipolar small-molecule medium. Neither increased bias current size nor reversed polarity can downsize junction MR response in the spin valves based on these conjugated polymers hence verified underlying great potential of ambipolar media in spintronics devices. We would like to emphasize that no spinterface effect happened even when these solution-processed polymers contacted directly with ferromagnetic electrodes according to comprehensive magnetization study. This spin-related exploration opened a new avenue to understand spintronics from material level, and also unveiled inspiring potential of solution-processed D-A type conjugated polymers on future spin-memory devices.