Synthesis And Properties Of Small-molecule Acceptor Materials Based On Indacenodithiophene And Indacenodithieno-thiophene Groups

In recent years,non-fullerene acceptor materials have become a research hotspot in the field of organic solar cells（OSCs）.At present,the energy conversion efficiency（PCE）of OSCs based on organic small molecule non-fullerene acceptor materials has exceeded 18%.The chemical structure of high-efficiency organic small molecule receptors（SMAs）materials is generally ADA or A-π-D-π-A.The central D unit is usually composed of polycyclic fused aromatic hydrocarbons,and the A units at both ends are generally electron withdrawing units,π-conjugated bridges are commonly used electron-rich aromatic heterocycles.The terminal A andπ-conjugated bridge have an important influence on the molecular structure,photoelectric properties and photovoltaic performance of the SMAs.At this stage,most of the ends are2-（3-oxo-2,3-dihydro-1H-inden-1-ylidene）malononitrile（IC）and its derivatives,and most of theπ-conjugated bridges are thiophene and Its derivatives,other highly efficient A units andπ-conjugated bridges are rarely reported.Based on this,this thesis introduces new electron withdrawing terminal A andπ-conjugated bridges to design and synthesize a series of new small molecule receptor material,Based on high-efficiency central D dithiophene（IDT）and dithienothiophene（IDTT）.The effects of different terminal A units andπ-conjugated bridges on the thermal properties,photophysical,electrochemical properties and photovoltaic properties of the synthesized SMAs were studied in detail.The main research contents are as follows1.A series of small molecule acceptors（IDT-PCN,IDT-TCN,IDT-T-PCN and IDT-T-QPCN）with IDT as the center of the electron-donating D unit were prepared by alkynes and tetracyanoethylene（TCNE）or tetracyanoquindimethane（TCNQ）in series[2+2]-cycloaddition/reverse electrochemical reaction.The introduction of different electron-withdrawing terminals A andπ-conjugated bridges and their effects on the thermal stability,photophysical,electrochemical and photovoltaic properties of small molecule acceptor materials were studied in detail.The results show that the absorption spectra and energy levels of IDT-PCN at the end of benzene ring containing cyano group and IDT-TCN at the end of thiophene containing cyano group are similar.However,after adding theπbridge,the absorption spectrum of IDT-T-PCN will show a substantial red shift,the LUMO energy level will increase,and the conjugation length will be further expanded.The absorption spectrum of the small molecule IDT-T-QPCN will be further red shifted,and the absorption sideband will reach 1100 nm,and increase the LUMO energy level and reduce the HOMO energy level at the same time.The photovoltaic performance of OSCs constructed with the medium band gap polymer PBDB-T as the donor material and four small molecules as the acceptor material is not ideal.Among them,the device based on IDT-TCN:PBDB-T obtained an efficiency of 0.63%.2.Using carbon-carbon double bonds and carbon-carbon triple bonds asπ-conjugate bridges,two A-π-D-π-A small molecules（IDT-VT-IC and IDT-ET-IC）with IDT as the center D unit and IC as the terminal A unit were designed and synthesized.Due to the poor solubility of the small molecule IDT-VT-IC with carbon-carbon double bonds,the device performance test cannot be performed.Therefore,the focus is on the thermal stability and optical stability of the carbon-carbon triple bond as aπ-conjugated bridge.Influence of physical,electrochemical and photovoltaic properties.The results show that:IDT-ET-IC has better thermal stability than IDT-T due to the reduced bond energy by adding carbon-carbon triple bond.Due to the electron-deficient nature of the carbon-carbon triple bond unit,the material is connected by carbon-carbon triple bond.It usually shows a blue-shifted absorption spectrum.Compared with IDT-T,IDT-ET-IC has a blue-shifted spectrum.The LUMO energy level of IDT-ET-IC and IDT-T is not much different,but the HOMO energy level is somewhat different.reduce.Using polymer PBDB-T as the donor material and small molecule IDT-ET-IC as the acceptor material,bulk heterojunction OSCs devices were fabricated.After preliminary testing,OSCs based on PBDB-T:IDT-ET-IC finally achieved a PCE of 4.52%.3.Using IC’s double halides IC-ClBr and IC-FBr as the terminal electron-withdrawing A units,two SMAs materials IT-ClBr and IT-FBr with IDTT as the center D unit were designed and synthesized.The focus is on the effects of different double halogen atom substitution terminals on the thermal stability,photophysical,electrochemical and photovoltaic properties of SMAs.The results show that the fine adjustment of the terminal halogen atom has a certain influence on the absorption spectrum of the molecule.The absorption spectra of IT-ClBr and IT-FBr in both solutions are almost the same,but in the case of thin films,IT-FBr absorbs more strongly at 300-750 nm.From the energy level,the LUMO and HOMO energy levels of IT-FBr are slightly lowered,which is conducive to obtaining high V_OC.The OSCs prepared by using the medium-bandgap polymer PM6 as the donor have been optimized,and the PCEs of OSCs based on PM6:IT-ClBr and PM6:IT-FBr are 10.88%and 12.35%,respectively.The JSC and FF of the two are not much different,mainly because the V_OCof IT-FBr has been greatly improved,making the PCE of IT-FBr higher than IT-ClBr.