Ferroelectric organic field-effect transistors (Fe-OFETs) have attracted intensive attention because of their promising potential in nonvolatile memory devices. The quick switching between binary states is a significant fundamental feature in evaluating Fe-OFET memories. Here, we employ 2D molecular crystals via a solution-based process as the conducting channels in transistor devices, in which ferroelectric polymer acts as the gate dielectric. A high carrier mobility of up to 5.6 cm2 V–1 s–1 and a high on/off ratio of 106 are obtained. In addition, the efficient charge injection by virtue of the ultrathin 2D molecular crystals is beneficial in achieving rapid operations in the Fe-OFETs; devices exhibit short switching time of ∼2.9 and ∼3.0 ms from the on- to the off-state and from the off- to the on-state, respectively. Consequently, the presented strategy is capable of speeding up Fe-OFET memory devices by using solution-processed 2D molecular crystals.Keywords: 2D molecular crystals; ferroelectric organic field-effect transistor memory; high-speed organic transistor memory; nonvolatile; solution processed;

Solution-processed 2D organic crystals are of significant interest because of their unique characteristics that ensure promising applications in electronics. In this study, a simple and efficient approach to directly write 2D organic crystals using a rollerball pen has been presented. The obtained crystals exhibit highly crystalline features with atomic smoothness and large size. Field-effect transistors composed of the obtained crystals yield an average and a maximum carrier mobility values of 3.1 and 5.9 cm2 V−1 s−1, respectively. This study presents significant potential of the writing technique via a rollerball pen for the solution-processed fabrication of 2D organic crystals for high-performance, large-area printed electronics.

•Organic semiconducting crystals were directly written by rollerball pens for OFETs.•A facile and rapid approach for the growth of solution-processed organic crystals.•High performance with μFET of 0.7 cm2/Vs and on/off ratio of 107 was obtained.•Solution flowing behavior benefits formation of crystals with large grain sizes.To deposit organic semiconducting crystals from solution, we propose the use of a rollerball pen as a simple and promising tool. These organic crystal grains of dioctylbenzothienobenzothiophene measured several hundred micrometers. The fabricated OFETs exhibited good device performance with a field-effect mobility (μFET) of 0.7 cm2/Vs and an on-off ratio of more than 107. Simulation results reveal that the flow behavior of solution from the pen refill tube to the substrate intrinsically enhances the formation of large organic crystals.Graphical abstract

•We fabricated OTFTs with CuPc films grown under different deposition pressures.•Enhanced device performance was obtained at high deposition pressure.•Deposition pressure modulated CuPc molecular packing and orientation.•Contact resistance decreased when deposition pressure increased.Copper phthalocyanine (CuPc)-based thin film transistors were fabricated using CuPc films grown under different deposition pressure (Pdep) (ranging from 1.8 × 10−4 Pa to 1.0 × 10−1 Pa). The transistor performance highly depended on Pdep. A field-effect mobility of 2.1 × 10−2 cm2/(V s) was achieved under 1.0 × 10−1 Pa. Detailed investigations revealed that Pdep modulates the molecular packing and orientation of the organic films grown on a SiO2/Si substrate and influences the charge transport. Furthermore, from a device physics point of view, contact resistance of the fabricated transistors decreased when Pdep increased, which was beneficial in reducing energy consumption.Graphical abstract

•Large PCBM single crystals with >150 μm in size were formed using SVA.•Influences of substrate and solvent vapor for PCBM crystal growth was investigated.•Our method was used for a spontaneous formation of PCBM and C8-BTBT crystals.We propose that solvent-vapor annealing is an efficient method for fabricating large [6,6]-phenyl C61 butyric acid methyl (PCBM) single crystals. The morphology and size of PCBM crystals are influenced by different substrates and annealing solvents. Hexagonal PCBM crystals >150 μm in size were obtained when crystallization was performed on bare SiO2 substrate under the saturated vapor of chloroform for annealing. The proposed method was also applied to a bi-component system, which led to the spontaneous formation of PCBM and dioctylbenzothienobenzothiophene single crystals.