Photoinduced sign change of the magnetoresistance in field-effect transistors based on a bipolar molecular glass

Abstract

The application of a novel bipolar molecular glass in field-effect transistors leads to devices with photoinduced magnetoresistance (MR) sign change. In darkness a low external magnetic field increases the resistance (positive MR up to +0.1%), while a magnetic-field induced resistance decrease (negative MR up to -6.5%) can be achieved under illumination.

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

“…The change in magnetoresistance polarity could be caused by temperature [19], voltage [20][21][22][23], magnet field [7,24] and illumination [17]. Here, we report MR sign change in a field-effect transistor.…”

“…Therefore, sign change in organic diodes could be caused by several physical parameters. In our previous work we also demonstrated photoinduced sign change of magnetoresistance in three-terminal devices organic field-effect transistors based bipolar organic conjugated molecules and one of our possible explanations is due to the bipolaron model [17].…”

“…The magnetic field was varied between À100 mT and +100 mT and all experiments were performed in darkness and at room temperature. The data acquisition process and the calculation of MR values have been described in details elsewhere [16][17][18]. The hole mobility and the threshold voltage have been calculated at the saturation regime [26].…”

“…MR in this device has been observed in two different material systems and experimental conditions: (i) photoinduced MR in p-channel OFETs based on acene compounds [13][14][15] and (ii) MR in bipolar material systems such as in a binary mixture composed of electron donor and acceptor as well as in bipolar molecular glass [16,17]. Very recently, we reported MR effects in a unipolar p-channel OFET based on low molecular weight 2,2 0 ,7,7 0 -tetrakis-(diphenylamino)-9,9 0 -spirobifluorene (Spiro-TAD) and an interface doped system with organic molecular p-dopant 1,3,4,5,7,8-hexafluoro-tetracyanonaphthoquinodimethane (F6-TNAP) [18].…”

“…Our group has intensively studied the OMAR effects in organic field-effect transistors (OFETs) measured at room temperature and at low external magnetic field [13][14][15][16][17]. MR in this device has been observed in two different material systems and experimental conditions: (i) photoinduced MR in p-channel OFETs based on acene compounds [13][14][15] and (ii) MR in bipolar material systems such as in a binary mixture composed of electron donor and acceptor as well as in bipolar molecular glass [16,17].…”