Fig. 4a and b shows device performance data measured peri
odically in ambient conditions (air, moisture, and dim light) for a
pristine P3HT and a dual layer SiP3HT transistor after fabrication.
These FETs show large increase of OFF current and noticeable shift
of threshold voltage, which is due to the ambient airinduced
localized trap states at the P3HT and P3HT/dielectric interface
[40]. As a consequence, the bulk conductivity of the active channel
gradually increases, leading to a subsequent degradation of ON/OFF
current ratio.
Noteworthy is the case of SiP3HT nanocomposite. For about
350 h exposure to air, the dual layer transistor (N ¼ 0.3) was rela
tively stable with a reduction in saturation mobility from
2.55 102 cm2V1 s1 to 1.74 102 cm2V1 s1 (~30% reduction).
Even after 1500 h the mobility of the same device still remained at
0.53 102 cm2V1 s1, demonstrating sustained electrical per
formance without any encapsulation. Though more oxygen/water
getting absorbed in the active channel (see the schematic illustra
tion in Fig. 4c), the charge transport pathway (P3HTtoSi
nanowiretoP3HT) near the semiconducting/dielectric interface is
still accessible and thus alleviates mobility degradation. In contrast,
the pristine P3HT devices (N ¼ 0) showed a pronounced degrada
tion with mobility and have lost their transistor functionality in less
than 400 h. After 1700 h the SiP3HT device was temporarily heated
at 120 C for 30 min in N2; the IVs collected were still indicative of
transistor characteristics with a recovered mobility of 1.02 102
cm2V1 s1. This revival is most likely due to the removal of
physically absorbed oxygen and water molecules.
For an indepth understanding of the enhancing role of the
employed Si nanowires, further study will discuss the effect of
electrical conductivity of Si nanowires on the eld effect charac
teristics. Much study is also needed to identify the stability effect
from these heterogeneous composites and to learn how to control
them.