Magnetoresistance sign change in field-effect transistors via interface doping of Spiro-TAD with F6-TNAP

•We show magnetoresistance effect in organic field-effect transistors via interface doping.•A sign change of magnetoresistance is observed by tuning the drain and gate voltages.•Our results indicate the coexistence of two underlying mechanisms.

We report on an organic field-effect transistor with a magnetoresistance (MR) effect whose sign could be tuned by the applied voltage. To realize such a device we doped 2,2′,7,7′-tetrakis-(diphenylamino)-9,9′-spirobifluorene (Spiro-TAD) by inserting a thin layer of 1,3,4,5,7,8-hexafluorotetracyanonapththoquinodimethane (F6-TNAP) deposited between bare SiO2 gate dielectric and Spiro-TAD. Our measurements exhibit two MR components, indicating the coexistence of two underlying mechanisms. The first component with positive MR and a narrow line shape can be ascribed to the bipolaron model. The second component with negative sign and broad line shape can be understood as high-field effect and could be explained by the trion model. The interplay of both MR components results in a voltage-dependent MR with sign change.

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