Design,Synthesis And Properties Of Cyanoindanone-Based Simple Small Molecule Acceptor Materials

Non-fullerene acceptor（NFA）materials have become a research hotspot in organic solar cells（OSCs）due to their advantages of tunable molecular structure,wide absorption range,and tunable energy levels.At present,major breakthroughs have been made in A-D-A non-fullerene acceptors with fused-ring aromatic hydrocarbon units as the central core,and the power conversion efficiencies（PCE）of single-juncation OSCs prepared based on NFA materials have exceeded 19%.However,such NFAs have problems such as complex synthesis steps,high cost,and unclear structure-performance relationship,which hinders mass produc-tion and commercial applications of OSCs.Designing and synthesizing NFAs with simple structures and excellent performance simultaneously is the core to copy with these issues.Thus,this thesis carried out the design,synthesis and performance research of simple small-molecule acceptor（SMA）materials based on cyanoindanone unit.Three types of simple SMA materials were designed and synthesized with similar cyano-indanone unit and different central skeletons.The effects of central skeletons and cyanoindanone terminals on the thermal stability,optical electrochemical and photovoltaic properties are systemic studied for these obtained SMAs.This thesis reveals the molecular design laws of efficient and simple non-fused ring SMA materials,the main research content and research results of this thesis are summarized as follows:1.We designed and synthesized A-π-A_w-π-A type simple non-fused ring SMA material of BTz-4Cl-1 using weak electron-withdrawing methylbithiazole acceptor unit as central core（A_w）,alkylthiophene asπbridge,and dichlorocyanoindanone as strong electron-withdrawing terminal acceptor unit（A）.The thermal stability,crystallization,photo-physical,electrochemical and photovoltaic properties of BTz-4Cl-1 were studied in compared with the SMA material BTz-4F-1 using difluoro-cyanoindanone as the terminal group.The study revealed that:（1）BTz-4Cl-1 possesses excellent planarity with strongπ-πstacking,whose distance is 3.47（?）;（2）Compared with BTz-4F-1,BTz-4Cl-1shows lower highest occupied molecular orbital（HOMO）and lowest unoccupied molecular orbital（LUMO）energy levels（-5.99 and-4.03 e V）;（3）By using polymer J71 as donor,both SMAs as acceptor,the BTz-4Cl-1-based devices showed more severe phase separation than the BTz-4F-1-based devices,which result in significantly reduced photovoltaic performance.2.We designed and synthesized A-D-D’-D-A type simple fused-ring SMA materials BDT-2Ti C16-2CN and BDT-2Ti C16-2DFCN with benzo-dithiophene as the central electron-donating（D’）unit,bis（hexadecyl）-thienobenzopyran as the arm electron-donating（D）unit,cyanoindanone or difluorocyanoindanone as terminal strong electron-withdrawing（A）units.The thermal stability,photophysical,electrochemical and photovoltaic properties of these SMA materials were systemic studied.It is found that:（1）The twist angle between the thiophene ring on benzo-dithiophene and benzene ring on the adjacent thienobenzopyran is greater than 20°by theoretical calculation,which result in the reduced planarity and crystallinity of the molecule;（2）The introduction of three electron-donating units in the D-D’-D framework elevated HOMO and LUMO energy levels.As a result,the HOMO and LUMO energy levels of BDT-2Ti C16-2DFCN based on difluorocyanoindanone are-5.71 and-3.95 e V,respectively;（3）In the PM6:PC71BM binary fullerene OSCs,this kind of A-D-D’-D-A type simple fused-ring SMA material with weak crystallinity was introduced as guest-donor material,and the photovoltaic performance of ternary OSCs was significantly improved.Among them,BDT-2Ti C16-2DFCN showed a better promotion effect,the PCE was increased from 8.53%of binary device to 9.46%of ternary device.Moreover,the open circuit voltage(V_oc)was identical to the binary and ternary systems（0.96 V）.3.We designed and synthesized the A-D-D’-A type simple non-fused-ring SMA materials CBDT-Ti C8-2DFCN,CBDT-Ti C8-2DCl CN,CBDT-Ti C12-2DFCN,CBDT-Ti C12-2DCl CN and DTP-Ti C12-2DFCN based on a class of double electron-donating units（D-D’）with thieno-benzopyran and cyclopent[2,1-b:3,4-b’]dithiophene（CBDT）or dithieno pyrrole（DTP）as the arm,and difluoro-or dichloro-cyanoindanone as terminal strong electron-accepting（A）unit.The thermal stability,photophysicals,electrochemical,photovoltaic properties and surface energy of these SMA materials,as well as the molecular structure-property relationship,such as electron-donating unit structure,electron-withdrawing unit structure and alkyl chain structure,were studied.It is found that:（1）The twist angle between the dual electron-donating units is 21.31°～22.66°by theoretical calculation,which also result in the reduced planarity and crystallinity;（2）Such A-D-D’-A SMA materials present similar HOMO and LUMO energy levels in comparison with the A-D-D’-D-A type SMA materials,the HOMO energy level is in the range of-5.71～-5.57 e V and the LUMO energy level is in the range of-3.90～-4.11 e V;（3）In comparison to the DTP-Ti C12-2DFCN with DTP unit,the other four SMAs with CBDT unit exhibited significantly improved photovoltaic performance in the OSCs using polymer PM6 as the donor.The PCEs were increased to 9.11%～10.60%;（4）OSCs based on CPDT-Ti C12-2DCl CN exhibited the champion PCE of 10.60%.In this thesis,we systemic reveal the effect of molecular skeleton structure on material properties.More importantly,a class of simple non-fused-ring SMA materials using cyanoindanone as terminal was obtained,which provided an important reference for the development of efficient non-fused-ring SMA materials.