Molecular and Interfacial Adjustment of Magnetoresistance in Organic Spin Valves Using Isoindigo-Based Polymers

The organic interlayer is a crucial part in organic spin valves (OSVs), and its molecular structure has an important effect on the device performance. In this work, we utilized conjugated polymers based on isoindigo derivatives (PIID-TVTCN, PAIID-TVTCN, and PFIID-TVTCN) to fabricate OSVs and studied the dependence of the performance on the polymer structure. Positive magnetoresistance (MR) was obtained in OSVs with 40 nm polymeric thin films. Under the same conditions, the introduction of a pyridine nitrogen into the conjugated skeleton (PAIID-TVTCN) induced an increased MR value, while fluorine substitution in the isoindigo unit resulted in no change in MR. The relationship between structure and performance was further clarified. However, the MR was negative in OSVs with 25 nm polymeric thin films but flipped to positive when an AlOx film was inserted under the Co electrode. Thus, the negative MR was attributed to a synergistic effect between tunneling transport and interfacial coupling. The results highlight the effects of the polymer structure and thickness as well as the insertion of a layer of AlOx on the performance of OSVs and are also the first for this kind of multidimensional functionalized modulation of MR in polymeric-based OSVs.