Fabrication Of Wafer-Scale Organic Single-Crystal Films And Arrays Via Microspacing In-Air Sublimation

Organic semiconductors(OSCs)show broad application prospects in the field of consumer electronics in organic field-effect transistors(OFETs),organic solar cells and organic lightemitting diodes(OLEDs)due to their adjustable chemical structures,tunable optoelectronic properties,light weight and flexibility.The integration of OSCs into electronic circuits for practical applications require large-scale and uniform films or arrays.OSCs in single crystalline forms possess long range well-ordered molecular packing,fewer random grain boundaries and lower defect density when compared to their amorphous or polycrystalline counterparts.As a consequence,higher carrier transporting mobility,higher luminous efficiency,and even longer exciton diffusion lengthare presented in the OSC crystals.To date,the fabrication of large-scale single crystalline OSC films is still challenging due to the difficulties in controlling the continuity,uniformity and in-plane orientation during conventional vapor process.Due to the poor controllability of the crystallization process for the large-conjugated molecules,the prepared organic semiconductor crystals often suffer from random location,limited and ununiform crystal size,and disordered crystallographic orientation arrangement,which reduces device performance and uniformity greatly.To realize integrated devices application,it is essential to develop a patterning technology to grow patterned organic crystals.Considering the anisotropic physical properties(e.g.,the charge carrier mobility which is strongly dependent on the crystallographic orientations)of single crystal.The essential points to grow discrete single-crystalline patterns are to align the crystallographic orientation among the patterns besides controlling their deposition locations.Therefore,it is imperative to develop a new simple and universal method for preparing OSC single crystal films with large area,high crystallinity and uniform orientation.This thesis is based on the micro distance sublimation growth method invented by the research group,aiming to develop this method from growing isolated,randomly oriented single crystals to growing large area continuous single crystal films and single crystal arrays.Based on the control of substrate wettability,this thesis achieved the growth of C8-BTBT,C10-BTBT-Ph and other materials with large areas of single crystal films and arrays through precise control of the raw substrate,growth substrate,and growth process.The main contents of this paper include the following three aspects:1.Microspacing in air sublimation synthesis of large area single-crystalline films.Wafer scale and uniform orientation single-crystalline C8-BTBT films have been grown utilizing microspacing in air sublimation with substrate wettability treatment and controlling the distribution of raw material intermediate states.Large area C8-BTBT single crystal film has uniform orientation and high crystal quality proved by polarization microscope,scanning electron microscopy,transmission electron microscope,selected area electron diffraction,Xray diffraction and synchrotron radiation two-dimensional(2D)grazing incidence X-ray diffraction tests.5×7 transistor devices array was prepared on C8-BTBT film,displaying excellent electrical performance,all OFETs worked in the array with a device yield of 100%.The average saturation mobility is about 3.91 cm2 V-1 s-1 and the highest value was measured to be 5.61 cm2 V-1 s-1,the reliability factors ranging from 74.2%to 99.5%with the relative variation in mobility was 19%,which is at the leading level of similar devices.Moreover,the transistors possessed nice stability,whose mobility can be remained without degradation at least for four months.2.Microspacing in air sublimation synthesis of patterned single-crystalline arrays.We successfully grow large-scale patterned organic single crystal array relies on selective growth of C8-BTBT on the surface with different wettability.To resolve the random orientation,interconnecting pattern motifs was designed to induce dependent crystallization of all the pattern units.A uniformly oriented C8-BTBT single crystal array was obtained using continuous crystallization of liquid crystal intermediate states.The uniform orientation of the patterned crystal makes the average carrier mobility of the field effect transistor based on C8-BTBT is 6.28 cm2 V-1 s-1,and the maximum carrier mobility can reach 9.67 cm2 V-1 s-1.3.Growth of organic thin film crystals on flexible substrates by microspacing in air sublimation.We have explored the growth of large-area organic thin film crystals and patterned crystal arrays using different flexible substrates by microspacing in-air sublimation assisted with surface wettability treatment.Large-area continuous C8-BTBT crystal films were successfully obtained on PVA and PI films,and patterned C8-BTBT crystal arrays were obtained on PI films,providing new method for the fabrication of flexible organic single crystal devices.