Figure 4 (a) Schematic illustration of the OFET device.
Transfer curves of the (b) AG1, (c) UG1, and (d) DG1 based OFET devices
for the programming and erasing processes.
To gain an insight into the specific characteristic of nanogrids, we
designed and fabricated the organic field effect transistor (OFET)
memory devices, in which the as prepared AG1, UG1 and DG1 thin films
served as charge trapping layers (CTL). The sketch mapping of the
devices was shown in Figure 4a and the detailed fabrication procedures
were given in section VII in the supporting information. The transfer
curves of the devices were shown in Figure S7a-c. All the fabricated
devices exhibited typical p-type behavior with the hole carrier mobility
of about 0.6
cm2V-1s-1 and
ION/IOFF over 104. As
shown in Figure S7d-f, the output characteristics of the devices show
good current modulation with well-defined linear and saturation regions.
The transfer curves before and after different stimulus conditions were
further investigated and shown in Figures 4b-d. The memory window
(ΔVth) is defined as the difference between the
threshold voltage (Vth) of the programmed and erased
states. For the programming process, when applying a gate voltage
(VGS) of 40 V with 145 mW/cm2 for 1 s,
the photogenerated electrons could be trapped by the CTL, resulting in
the positive shift (ΔVth-e) of the transfer curves. For
the erasing process, with a reverse VGS of ‒30 V under
dark for 1 s was applied, the transfer curves shifted to the negative
direction (ΔVth-h) owing to the holes transfered from
pentacene and trapped by the CTL. The ΔVth of AG1, UG1
and DG1 devices were calculated to be 28.3 V, 12.7 V and 20.5 V,
respectively. In comparison, AG1 device show the largest
ΔVth with the largest ΔVth-e and
ΔVth-h generated in the programming and erasing
processes, indicating the excellent electron and hole trapping capacity
of AG1 and suggesting the rigid skeleton of nanogrids can be benefit for
realizing high performance OFET memory devices.
Conclusions
In summary, we have designed and synthesized a novel series of A-type of
axially and centrally chiral nanogrids (AGs) comprising difluorenyl
biaromatic derivatives and thiophene derivatives. Our study found that
using R /S -BINDFOH (15-20%) as the substrate, as the
substrate resulted in a significantly higher yield of AGs compared to
mixed BINDFOF (9%). Furthermore, the relevant characteristics of AG1,
UG1 and DG1 based OFET memory devices show that nanogrids possess large
electron/hole trapping capacity, the AG1 is expected to become the star
material for the new generation of semiconductor devices. These findings
provides us with a simple and direct synthetic approach to access an
array of nanogrids intelligently fused with chiral skeletons, which
contribute to the further discovery and application of attractive
organic nanogrids.
Experimental