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

Abstract

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.