Fabrication Of Organic Single-crystalline P-n Heterojuctions Arrays And Their Application In Field-effect Transistors

Organic semiconductor single crystals have recently aroused increasing interest due to their unique optoelectronic properties.However,the scale-up of organic singlecrystalline p-n heterojunctions for large-scale applications is still difficult because the growth orientation and location of organic semiconductor single crystals are usually random and disordered in nature.In this thesis,a series of solution-processed strategies were developed for the fabrication of organic single-crystalline p-n heterojunctions arrays,and high-performance field-effect transistors(FETs)based on organic single-crystalline p-n heterojunctions arrays were successful fabricated.These results are summarized as follows:1.Fabrication of bilayer p-n heterojunction single-crystalline microbelt arrays and their application in ambipolar field effect transistorsIn this work,large-area bilayer single-crystalline p-n heterojunction microbelt(MB)arrays of TIPS-PEN and BPE-PTCDI have been successfully fabricated by a surfaceenergy-decided gradually positioning crystallization(SEGPC)method.By using 3D SU-8 channel template,the wetting location and crystalline positioning of p-type and n-type microbelt arrays can both be controlled at the edges of SU-8 where it has a high surface energy.Simultaneously,an external force was applied to the template to guide the unidirectional solution spreading at the edge of photoresist stripe,leading to aligned largearea bilayer single-crystalline p-n heterojunction microbelt arrays,as well as regular molecular packing.OFETs based on the junctions showed ambipolar charge transport characteristics,with the best performance of 0.526 cm2 V-1 s-1 for hole mobility and 0.342 cm2 V-1 s-1 for electron mobility,respectively,that are the highest reported values among organic small-molecule single-crystal-based ambipolar transistors.Moreover,OFETs based on MB p-n heterojunction arrays exhibit stable devices performance with average hole and electron mobilities up to 0.45 cm2 V-1 s-1 and 0.27 cm2 V-1 s-1 of 40 devices on the same substrate,respectively.We also demonstrated that complementary inverters can be constructed using the bilayer p-n heterojunction MB arrays,showing a gain value of 17.Therefore,we can fabricate large-area bilayer single-crystalline p-n heterojunction microbelt(MB)arrays through this method.This method has obvious advantages in building large-scale high-performance organic integrated electronic devices,which provides a new strategy for the realization of organic integrated circuits in the future.2.Fabrication of organic bulk heterojunction microbelt arrays and their application in ambipolar field effect transistorsIn this work,large-area organic p-n bulk heterojunction microbelt arrays have been successfully fabricated by dragging a blend solution of p-type TIPS-PEN,n-type TIPSTAP and polymer PS on the surface of water.We also systematically investigate the effect of different growth parameters(phase separation velocity,dragging speed and p/n ratio)on the microbelt arrays morphology and ambipolar carrier transport properties.Ambipolar OFETs based on p-n bulk heterojunction microbelt arrays exhibit relatively balanced hole and electron mobilities,with the best performance of 0.06 cm2 V-1 s-1 for hole mobility and 0.01 cm2 V-1 s-1 for electron mobility,respectively.Meanwhile the current switch ratio(Ion/Ioff)of the devices is 106.Moreover,OFETs based on p-n bulk heterojunction microbelt arrays exhibit stable devices performance with average hole and electron mobilities up to 0.035 cm2 V-1 s-1 and 0.007 cm2 V-1 s-1 of 40 devices on the same substrate,respectively.In addition,the inverter based on MB arrays also shows good device performance,and its voltage gain can reach up to 16,which shows the possibility of application in high-integrated organic circuits.3.Fabrication of large-are organic semiconductor single-crystalline films and their application in field effect transistorsIn this work,a facile method that combines saturated vapor with shallow photoresist channels is developed for large-area growth of organic single-crystalline films.In this method,the DCB saturated vapor is used to increase crystallization time of C8-BTBT to improve crystal quality.At the same time,a slope with 5° and shallow photoresist channels provide a shearing force and capillary force,respectively.It can induce the crystallizations of organic semiconductor molecules along uniaxial direction.With the evaporation of solvent,large-area C8-BTBT single-crystalline films can be formed on the substrate.The surface roughness of the obtained film through this method is as low as ~12 nm and the maximum area of film is 1.5 cm × 1 cm,which represents the best result among previous reports.Meanwhile we also systematically investigate the effect of photoresist channels depth on the morphology of the C8-BTBT single-crystalline films.The growth process for C8-BTBT single-crystalline films is described in detail by the insitu polarized microscope observations.The p-type FETs based on the single-crystalline C8-BTBT films are fabricated with mobilities up to 0.9 cm2 V-1 s-1 and average mobility up to 0.65 cm2 V-1 s-1 of 40 devices on the same substrate.The current switch ratio(Ion/Ioff)of FETs is 106.The devices are very stable and their mobilities are equivalent to that of commercial FETs based on amorphous silicon(?-Si)(mobility 0.1~1 cm2 V-1 s-1),which is expected to used widely in the field of large-scale organic integrated devices.