Study On The Design And Synthesis Of D-A And Star-shaped Organic Small Molecules And Their Resistive Information Storage Mechanism

Nowadays,human society is in the irreversible process of globalization and informatization.Each of us is inextricably linked with information and data.Silicon-based semiconductors have gradually approached their physical limits,and at the same time,the computing bottleneck of the Von neumann structured computers has gradually emerged.Therefore,it is urgent to explore new semiconducting materials and new memory devices with high density,low power consumption,high switching speed and high reliability.Organic small molecules have attracted extensive attention for application in information storage due to the merits of low cost,easy purification,well-defined structures,and excellent solution processability.This dissertation mainly focuses on the electronic and steric hindrance effects of different terminal substituents and the influence of the bridge bonds between the donor(D)and acceptor(A)on the electrical storage performance of memory devices based on the D-A type organic small molecules.The electronic structure and topological geometry structure of star-shaped molecules on the performance of memory devices are also carried out.The details as follow:(1)To explore the influence of different terminal substituent groups on the memory data storage performance,three new D-A type molecules X-TBT were designed and synthesized,all of which have a molecular backbone consisting of two triphenylamine(T)groups and a benzothiadiazole(BT)group,but have terminal substituent groups(X)with different electronic and steric hindrance effects,that is,cyano(CN),tert-butyl(^tBu)and methoxy(OMe),named CN-TBT,^tBu-TBT and OMe-TBT,respectively.Then,these D-A type molecules were used as active materials to prepare organic electrical storage devices and conduct in-depth systematic research on their performance.The results show that altering the substituents in D-A molecules can adjust the molecular packing,thin film morphology and electron trap depth of active layer,which then significantly influence the memory performances.Nonvolatile ternary write-once-read-many-times(WORM)data storage behavior is achieved for the CN-TBT and ^tBu-TBT based devices as compared to the binary memory characteristic of TBT(X=H).In contrast,OMe-TBT based device still maintains binary WORM behavior due to its unfavorable molecular packing motif and weak intermolecular charge transfer effect,but exhibits the lowest threshold voltage(V_th=1.4 V)as a result of the lowest energy barrier between electrode and active layer.Notably,^tBu-TBT-based device displays the highest I_ON2/I_ON1/I_OFF ratio of10⁷:10³:1.This has a very promising application for developing memories with low power consumption and high density.(2)On the basis of the research of chapter 2,in order to further reduce the V_th of the memory,three new conjugated D-?-A type small molecules(X-TEBT)were synthesized by introducing an ethynyl groups between the D and A units.The corresponding organic memory devices were also prepared.Experimental results show that the insertion of?bonds increases the degree of molecular conjugation,which can effectively promote intramolecular charge transfer and improve the quality of the film,thereby greatly reducing the V_th of memory devices.It is proved that the modification effect of tert-butyl can improve the storage performance of organic electricity by single crystal structure of ^tBu-TEBT.In addition,we also tried the solution spin-coating method to fabricate a series of organic memory devices.As a result,the ^tBu-TEBT-based device still displayed the highest I_ON2/I_ON1/I_OFF ratio of 10⁷:10³:1 and the lowest V_th(V_th1=1.4 V,V_th2=2.6 V).The research results of this part provide solid experimental data and theoretical basis for the fabrication of low-cost,low power consumption organic multilevel memory devices.(3)After investigating the relationship between molecular structure and memory performance in one-dimensional direction,in order to understand the two-dimensional structure of the molecule on the memory behavior,we designed and synthesized a series of small organic molecules(TPPA,TPPT,BPPCz and BPPT)with high yield,high stability and star-shaped topology geometry.The organic memory devices based on TPPA,TPPT and BPPCz exhibited non-volatile binary WORM storage characteristics.It is found that the charge transfer from HOMO to LUMO might be the main reason for the resistive switching behavior.Due to the lowest energy barrier,compact?-?stacking mode,and smoother surface of TPPA,the TPPA-based memory device showed the lowest threshold voltage(1.5 V)and the highest I_ON/I_OFF ratio(10³:1).However,due to poor energy level matching of TPPT-based device,the V_th distribution of the TPPT-based device is quite wide.The increase in V_th of BPPCz-based devices is mainly caused by the rougher film due to the large diagonal surface of BPPCz.BPPT-based devices do not show electrical storage behavior due to incomplete charge transfer and poor film stacking.These results may provide new ideas for further exploration of low-cost,high-performance organic resistive switching materials and memory devices.In summary,by introducing tert-butyl moiety and ethynyl conjugated bridge unit in D-A molecules,and the memory performance has been effectively improved.At the same time,the storage behavior of high-yield organic star-shaped small molecules was explored.The research results in this dissertation provide experimental data and theoretical proof for the preparation of low cost,low power consumption organic multi-level memory devices,and lay a solid foundation for the commercialization of organic active materials in high-performance organic RRAM.