| Inkjet printing patterning of organic semiconductor molecular crystals provides a simple way to construct low-cost,large-area integrated organic circuits.However,due to the lack of methods to control nucleation and growth,the inkjet-printed organic crystals have heterogeneous morphology,uneven crystal orientation and poor crystallization,which is difficult to meet the requirements of practical device applications.In view of the above problems,this paper carries out research in the following aspects:1.Preparation of patterned C8-BTBT crystal arrays via microchannel assisted inkjet printing for organic field-effect transistorsIn this work,a microchannel assisted inkjet printing method is developed to achieve patterned organic semiconductor crystal arrays with uniform crystal orientation.Firstly,the solution is injected into the hydrophilic/hydrophobic microchannel pattern by inkjet printing.The crystal is preferentially crystallized and nucleated at tips of the channel because of the large solvent evaporation flux.Due to the limit of microchannel,the ink is oriented to de-wet and guide molecular ordered mass transfer,which improve the uniformity of crystal orientation.Finally,we can obtain patterned Cs-BTBT micron-band crystal array with uniform crystal orientation.In addition,the patterned C8-BTBT array has a unidirectional crystal orientation in a large area by analysis of polarization optical microscope(POM)and grazing incidence X-ray diffraction(GIXRD).Furthermore,the patterned C8-BTBT micron-band crystal based 7 x 7 organic field effect transistor(OFETs)array shows high average mobility of 3.23 cm2 V-1 s-1,along with maximum carrier mobility up 5.36 cm2 V-1 s-1.Meanwhile,the threshold voltage of OFET is about-7 V,the current on/off ratio is>107,and the subthreshold swing is about 1.87 V dec’1,which indicates a good electrical performance of the OFETs array.At the same time,due to the universality of this method,it can be applied to TIPS-PEN and other organic small molecule semiconductor materials.These results demonstrate that microchannel assisted inkjet printing method can effectively solve the problem of random orientation of organic crystals,and provides a new way for preparing patterned organic crystal arrays with uniform morphology and structure.2.Inkjet printing assist melt process of patterned Cg-BTBT liquid crystal films for application in organic field-effect transistorsIn this work,an inkjet print assisted melt process method is developed to realize the patterned growth of liquid crystal(LC)organic small molecule crystals with high crystallization and large grain size.The ink is injected into the hydrophilic/hydrophobic microtanks to get the ring like C8-BTBT crystals.Next,the LC material in microtanks is melting into liquid phase and spread out in the pattern due to the high surface energy of the interface.After that,the liquid C8-BTBT recrystallize by a very slow cooling process.By this method,we have successfully obtained patterned C8-BTBT LC film array with high crystalline and large grain size.The uniform crystal orientation of C8-BTBT LC film in large crystal domains is verified by characterizations of POM and transmission electron microscopy(TEM).In addition,we construct a discrete 7 × 7 OFETs array based on patterned LC films with the highest carrier mobility up to 9.33 cm2 V-1 s-1,and the average mobility of 6.31 cm2 V-1 s-1.Meanwhile,the threshold voltage of OFET device is about3 V,the device’s on/off ratio is about 105,and the subthreshold swing is about 1.27 V edc1,which indicate a high-performance of the OFETs array.As a results,an inverter based on the patterned LC films reach a high gain up to 23.75 and an exceptionally large static noise margin(SNM)over 81.3%.The SNM value obtained is one of the highest values reported in organic or metal-oxide-semiconductor based inverters.This method effectively solves the "coffee ring" effect in the crystallization process of liquid crystal small molecules,and greatly promotes the application of the liquid crystal materials in organic electronic devices.3.C8-BTBT growth with high crystalline on liquid-liquid interface for organic field-effect transistorsIn this work,we develop a method for growing C8-BTBT crystals on liquid-liquid interface,and realize the growth of patterned organic crystal arrays with high crystalline.Firstly,the ink which consists of solvent and anti-solvent is injected into the hydrophilic/hydrophobic pattern by inkjet printing.Due to the high boiling point of the anti-solvent,the solvent in the surface volatilizes quickly and prompts the bottom solution to be continuously replenished to the surface,which will eventually lead to the separation of the solvent and anti-solvent.The resulting liquid-liquid interface provides a good interface for the self-assembly growth of C8-BTBT small molecules.Finally.the uniform patterned organic crystal arrays with high crystalline are successfully prepared by this method.The high crystalline of the crystal is proved by the characterization of POM,atomic force microscope(AFM)and TEM.Furthermore,the patterned C8-BTBT crystals based 8 × 8 OFET array shows high average mobility of 6.89 cm2 V-1 s-1,along with the highest carrier mobility up to 9.83 cm2 V-1 s-1.In addition,the threshold voltage of OFET device is about-7 V,the current on/off ratio is about 107,and the subthreshold swing is about 1.05 V edc-1.Moreover,a NAND gate logic circuit is constructed based on the patterned C8-BTBT crystal film and the corresponding logic signal output in the integrated circuit can be obtained by testing.This method by constructing a liquid-liquid interface has high crystalline quality and solves the "coffee ring" effect of organic crystals in inkjet printing.It can provide a new idea for preparing patterned organic crystal films with high crystal quality by inkjet printing.4.Controlled nucleation of C8-BTBT single crystal by three phases contact line for high performance organic field-effect transistorIn this work,a nucleation method controlled by three-phase contact line is developed to realize the patterning growth of C8-BTBT organic single crystal.This method is based on the liquid-liquid interface growth mechanism,and the nucleation control is carried out by further changing the shape of the three-phase contact line of the ink droplet.The mixed ink is injected into the leaf-like hydrophilic/hydrophobic pattern by inkjet printing.Since the evaporation flux at the tip of the leaf-like three-phase contact line is much higher than other positions,which lead to the preferentially nucleation of organic molecules at this site.Then,C8-BTBT small molecules are epitaxially grown at the liquid-liquid interface to obtain organic single crystals and finally fill the entire pattern.It is proved that the obtained C8-BTBT crystal is single crystal by characterization of POM,TEM and GIXRD.The bottom-gate top-contact OFET array is constructed based on the patterned C8-BTBT single crystal.The 64 OFETs show high average mobility of 9.54 cm2 V-1 s-1 along with the maximum carrier mobility up to 12.35 cm2 V-1 s-1.In addition,the current on/off ratio of the device is about 109,the threshold voltage is about-5 V,and the subthreshold swing is about 510 mV dec-1.The test results show that the OFETs have excellent electrical performance.Moreover,a multiplier logic circuit is constructed for demonstration and the corresponding logic signal output can be obtained through the test of the circuit.This method of controlling crystallization by changing the shape of the three-phase contact line solves the problem of disordered growth of organic crystals in inkjet printing,and provides a new method for preparing organic single crystals with high crystalline quality by inkjet printing. |
