Sign Inversion of Magnetoconductance in Organic Semiconductors by Different Spin-Mixing Channels at Charge-Transfer Interfaces

Organic semiconductors have shown obvious spin-related magnetoconductance (MC) even without the involvement of any magnetic elements, bringing an emerging research field called as organic spintronics. Tuning the MC sign is crucial to realize practical application based on these spin effects. Herein, we report the manipulation of MC signs in organic photodiode based on the ground-state and excited-state charge–transfer (CT) interfaces at room temperature. Different to the traditional CT interfaces that normally show positive MC, the ground-state CT (GSCT) interface presents negative MC due to the dominant spin-mixing channel from weakly bound polaron-pairs states, in which a main reverse intersystem crossing from the triplet to singlet states will lead to the opposite signs of magnetic field dependence. By adjusting the ground-state or excited-state CT process in one tandem device under electric and optical excitations, the device could reveal a low-field controlled current inverter. Our work shows the important role of organic CT states in the manipulation of the spin-related magneto-optoelectronic properties in organic semiconductors.