Abstract
Efficient charge injection is critical for flexible organic electronic devices such as organic light-emitting diodes (OLEDs) and field-effect transistors (OFETs). Here, we investigated conjugated polymer-wrapped semiconducting single-walled carbon nanotubes (s-SWNTs) as solution-processable charge-injection layers in ambipolar organic field-effect transistors with poly(thienylenevinylene-co-phthalimide)s. The interlayers were prepared using poly(9,9-di-n-octylfluorene-alt-benzothiadiazole) (F8BT) or poly(9,9-dioctylfluorene) (PFO) to wrap s-SWNTs. In the contact-limited ambipolar OFETs, the interlayer led to significantly lower contact resistance (Rc) and increased mobilities for both holes and electrons. The resulting PTVPhI-Eh OFETs with PFO-wrapped s-SWNT interlayers showed very well-balanced ambipolar transport properties with a hole mobility of 0.5 cm2V-1S-1 and an electron mobility of 0.5 cm2V-1S-1 in linear regime. In addition, the chirality of s-SWNTs and kind of wrapping of conjugated polymers are not critical to improving charge-injection properties. We found that the improvements caused by the interlayer were due to the better charge injection at the metal/organic semiconductor contact interface and the increase in the charge concentration through a detailed examination of charge transport with low-temperature measurements. Finally, we successfully demonstrated complementary ambipolar inverters incorporating the interlayers without excessive patterning.
Highlights
Charge injection from metal electrodes into organic semiconductors (OSCs) is one of the critical issues in realizing high-performance organic electronic devices, because most of these devices contain Schottky-type metal-semiconductor contacts[1,2]
A top-gate and bottom-contact (TGBC) staggered device structure (Fig. 1a) was used, because the interlayer can be applied on the pre-patterned Au source and drain electrodes by a simple solution process and a semiconducting layer can be effectively passivated by the overlying gate dielectric and gate electrode layer to minimize degradation of the device by oxygen and moisture in the air
The interlayer solution was prepared by selectively wrapping semiconducting single-walled carbon nanotubes (s-single-walled carbon nanotube (SWNT)) using F8BT or PFO, similar to the previously reported processes involving only simple sonication followed by a mild centrifugation step[33,34]
Summary
Charge injection from metal electrodes into organic semiconductors (OSCs) is one of the critical issues in realizing high-performance organic electronic devices, because most of these devices contain Schottky-type metal-semiconductor contacts[1,2]. In conventional silicon-based devices, heavily doping in electrodes enables the fabrication of Ohmic contacts, permitting efficient charge injection. Such an efficient doping technique on an atomic scale is unfeasible for organic devices[3,4,5]. In addition to the large Schottky barrier, inefficient charge injection could arise from significant charge trapping, structural OSC disorders, and additional effects induced by charge transfer at the contacts in downscaled devices[10]. More comprehensive research is needed to apply these techniques for further optimization of devices
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