Design,synthesis And Field Effect Properties Of New Ladder-type Organic Semiconductor Materials

In recent years,the rapid development of the organic electronics industry has attracted widespread attention.Organic compounds have the advantages of simple chemical modification,flexible preparation,and solution processing,which are more suitable for applications in flexible displays,flexible electronic skins,and sensors than inorganic materials such as silicon and gallium arsenide.The design and synthesis of organic semiconductor materials are the basis for researching of organic semiconductor functional materials and devices.The structure of the ladder-type organic semiconductor materials is connected by double-bond,which makes they have good stability.However,there are some problems such as low charge mobility and inadequate charge storage capacity,which severely limit the application and development of organic electronic devices.Therefore,the development of high-performance organic semiconductor materials still requires more in-depth research.In this article,the framework of s-indacene was chosen as the basic structural unit to construct new organic semiconductor materials and memory materials.The molecular configuration,front-line orbital energy level,and crystal packing model were controlled through appropriate molecular modification strategies to optimize the performance of materials.Then,organic field-effect transistor(OFET)and nonvolatile organic field-effect transistor memory(OFET-NVM)based on organic materials were prepared.Finally,detailed research on the relationship between material structure and device performance establishes general guidelines for the design and synthesis of high-performance organic semiconductor materials and charge trapping materials.The main research contents are as follows:1.We designed and synthesized two pyrene-fused azaindacene configurational isomers,syn-B2IPIO and anti-B2IPIO,which are axial symmetric and central symmetric,respectively.These two isomers were applied as charge trapping elements(CTE)for the electret layers in OFET-NVM devices.Although the two isomers have a nearly identical molecular structure,absorption spectra and HOMO/LUMO energy levels,they exhibit distinctly different charge trapping capabilities.The OFET-NVM devices based on anti-B2IPIO exhibit a moderate memory window about 25 V.In contrast,the devices based on syn-B2IPIO show a more than twice wider memory window(?59 V).The different charge trapping behavior of this pair of isomers are attributed to their different intermolecular interaction associated with molecular symmetry,resulting in different molecular packing behavior and film morphology.Our results reveal that controlling the molecular symmetry could be a new and efficient strategy for designing organic CTE for high-performance memory devices.2.Four organic semiconductor materials based on the IFDMN framework were designed and synthesized,named H-IFDMN,HO-IFDMN,HT-IFDMN,and BMA-IFDMN.The effects of heteroatom on carrier transport performance were studied by constructing OFET devices.The atoms of oxygen,sulfur,and nitrogen were introduced into the alkyl side chain and directly connected with the conjugated skeleton.Due to the fine-tuning of front-line orbital energy levels and molecular stacking model by heteroatoms,OFET devices based on these four materials exhibit different carrier transport performance.In particular,the compounds H-IFDMN,HO-IFDMN,and HT-IFDMN exhibited electron transport capabilities,while the compound BMA-IFDMN exhibited hole transport capability.Combined with theoretical calculations,we proposed a molecular design strategy that can adjust the energy levels of molecular frontier orbitals and molecular stacking by heteroatom side chains to modify conjugated skeletons.3.The alkyl chain of compound HT-IFDMN with good performance was modified.The influence of alkyl chains with different branches on the performance of single-crystal organic field-effect transistor(SC-OFET)devices was systematically studied.Alkyl side chains are often used to improve the solubility of organic semiconductor materials to meet the requirements of preparing devices with the solution method.T-IFDMN derivatives with different branched alkyl chains maintain good field-effect performance,and the electron mobilities of SC-OFETs based on(2eb)T-IFDMN and(2eh)T-IFDMN were significant improvement.Our research shows that reasonable side-chain design can not only improve the solubility of organic materials but also have an impact on the construction of single-crystal devices.4.Compound DTID-Cl with chlorine substituted for the?-position of thiophene in DTID was designed and synthesized,and OFET devices based on DTID and DTID-Cl were prepared.The ambipolar material with low carrier mobility was transformed into an n-type material with high mobility.The modification of chlorine atoms not only affected the energy level structure of the compound but also significantly changed the electron transport mode and molecular stacking.Compound DTID shows poor film morphology and crystallinity.On the contrary,the film of DTID-Cl has good morphology,larger grain size,and better crystal quality.When DTID-Cl was deposited on the substrate treated with octadecyltrimethoxysilane(OTMS),electron mobility as high as 0.71 cm~2·V^-1·s^-1 can be achieved.Therefore,the introduction of chlorine atoms into DTID molecules is an excellent molecular modification strategy for the construction of high-performance n-type organic semiconductor materials.