This article was submitted to Physical Chemistry and Chemical Physics, a section of the journal Frontiers in Chemistry
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Stability problem of organic semiconductors (OSCs) because of photoabsorption has become a major barrier to large scale applications in organic field-effect transistors (OFETs). It is imperative to design OSCs which are insensitive to visible and near-infrared (VNIR) light to obtain both environmental and operational stability. Herein, taking a 2,3,8,9-tetramethoxy [1,4]benzodithiino[2,3-b][1,4]benzodithiine (TTN2) as an example, we show that controlling molecular configuration is an effective strategy to tune the bandgaps of OSCs for visible-blind OFETs. TTN2 adopts an armchair-like configuration, which is different from the prevailing planar structure of common OSCs. Because of the large bandgap, TTN2 exhibits no photoabsorption in the VNIR region and OFETs based on TTN2 show high environmental stability. The devices worked well after being stored in ambient air, (i.e. in the presence of oxygen and water) and light for over two years. Moreover, the OFETs show no observable response to light irradiation from 405–1,020 nm, which is also favorable for high operational stability.
Organic semiconductors have attracted tremendous interest in recent days because of their tailorable optoelectronic properties by molecular design, as well as their potential low cost, large-area fabrication, and mechanical flexibility (
Herein, we show that controlling molecular configuration is an effective strategy to tune the bandgaps of OSCs for stable OFETs. 2,3,8,9-tetramethoxy [1,4]benzodithiino[2,3-b][1,4]benzodithiine (TTN2), whose skeleton is an isomer of dibenzo-tetrathiafulvalene (DB-TTF) (
We had reported the synthetic procedures of TTN2 previously (
Bottom-gate/top-contact OFETs were constructed with OTS-modified SiO2 (300 nm) as the gate dielectric layer. Source and drain electrodes were fabricated by stamping Au (80 nm) stripes on TTN2 microcrystals (
Optical and cross-polarized optical microscope (OM and POM) images were obtained with Nikon ECLIPSE Ci-POL polarized optical microscope. Tapping mode atomic force microscopy (AFM) images were measured using a Bruker Dimension Icon. X-ray diffraction (XRD) measurements were carried out in reflection mode at 45 kV and 200 mA with monochromatic Cu Kα radiation utilizing a Rigaku Smartlab diffractometer. Ultraviolet-visible and near-infrared (UV-Vis-NIR) absorption spectrum of TTN2 microcrystals was measured with a Agilent Technologies Cary Series UV-Vis-NIR Spectrophotometer. OFETs were characterized using a Keithley 4200 SCS in ambient environment at room temperature. The photo responses of the OFETs were measured with lasers with tunable power intensity. The laser power intensity was measured
Tetrathiafulvalene (TTF) has been extensively investigated as a strong electron donor in organic electronics (
Molecular structure and packing motifs of
Tetrathianaphthalene (TTN) is an isomer of TTF which differs structurally from the latter only in the arrangement of the two ethyne bridges. In contrast to the planar molecular configuration of TTF, TTN adopts an armchair-like configuration with a dihedral angle between the terminal ethene and the central tetratia-enthene of about 137° (
In order to investigate the charge transport properties, TTN2 microcrystals were prepared by a simple solution drop-casting method (
The charge transport properties and optoelectronic performances of TTN2 microcrystals were investigated by the construction OFETs with a bottom-gate top-contact configuration (
Judging from the UV-Vis-NIR absorption spectra and the optical bandgap of TTN2, OFETs based on TTN2 microcrystals are visible-blind.
In summary, by controlling the molecular configuration from planar to armchair, a highly stable OSC TTN2 is obtained. Because of the large bandgap, TTN2 exhibits no photoabsorption in the VNIR region. OFETs based on TTN2 are insensitive to VNIR light and show excellent stability. The devices worked well after being stored in ambient air and light for over two years. Aryl-fused tetrathianaphthalenes with armchair-like configurations might be a new class of stable OSCs for highly stable OFETs.
The original contributions presented in the study are included in the article/
LZ and XT contributed equally to this work. RL, XS, and WH conceived the idea and directed the project. YS and XS synthesized TTN2. LZ and XT grew TTN2 microcrystals, fabricated the devices, and measured the properties of the devices. ZL helped obtaining the energy levels of the molecule through theoretical calculations. JY, SY, and YS helped the OFETs fabrication and measurements. ZG and HZ helped the test of the UV-Vis-NIR absorption spectra of TTN2. LZ, XT, and RL wrote the paper. All authors analyzed the experimental results and contributed to the discussion.
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
The authors acknowledge finical support from the National Natural Science Foundation of China (No. 51873148 and 52073206).
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