Synthesis And Properties Of D-A-type Organic Small Molecules And Conjugated Polymers Based On Thiophene Or Thienoaryl Group

The development of economic society is closely related to energy.Today,under the double restriction of the fossil energy shortage and environmental pollution,energy and environmental problems have become a global focus and need to be solved urgently.Due to the incomparable advantagies such as inexhaustible,safety,no pollution,no regional restriction,the development and application of solar energy has become a new hot topic in the study of energy around the world.Among them,solar cells that convert solar energy into electricity have become the main focus of the research direction to develop and apply solar energy.Organic solar cells?OSCs?have become the main research direction of the solar cell and developed rapidly,due to the advantages of wide material sources,simple preparation technology,device flexibility in a large area and so on.In this dissertation,we simply introduced the development of organic solar cells,and summarized the photoactive materials in details,including organic small molecules,conjugated polymers and non-fullerene accceptors.In order to solve the existing problems of OPVs such as the shortage of high-performance donor materials,lack of theoretical guidance for designing high-performance molecules,a series thiophene or thieno-aryl units based D-A type organic photovoltaic materials were designed and synthesized.The molecular structures of these organic small molecules and polymeric monomers were fully characterized.Their opto-physical,electrochemical,thermal properties and charge mobilities of the designed materials were well investigated alonged with their theoretical calculations.The relationships between the molecular structures and photovoltaic performance were further investigated.And some high-performance photovoltaic materials were obtained.The key studies are listed as follows:1)A class of small molecules with a D?A-A'?₂ framework was designed and synthesized based on diketopyrrolopyrrole?DPP?and thieno[3,4-c]pyrrole-4,6-dione?TPD?as dual acceptors.Comparing with their counterparts which bearing an A-D-A architecture,the effects of the second acceptor of TPD on the photophysical electrochemical and photovoltaic properties of their resulting molecules were systematically studied.It was found that the D?A-A'?₂ SMs have wider absorption spectra and lower LUMO than the resulting A-D-A type SMs.BDTT?TPD-DPP?₂exhibited the best photovoltaic properties with a power conversion efficiency?PCE?of 4.25%and a short circuitcurrent(J_sc)of 10.08 m A/cm².2)A class of small molecules with a D?A-Ar?₂ framwork was designed and synthesized,which contain a donor?D?core of indacenodithiophene?IDT?,two acceptor?A?arms of benzothiadiazole?BT?or fluorinated benzothiadiazole?DFBT?,and two terminals of 3-carbazole.The impacts of 3-carbazole and fluorine atom on the optical absorption,electrochemical property,hole mobility,film morphology,and solar cell performance were primarily studied.the IDT?DFBT-T3Cz?₂ showed a higher power conversion efficiency?PCE?of 5.99%with an increasing fill factor?FF?of59.6%than IDT?BT-T3Cz?₂ in their solar cells under the illumination of AM 1.5G at100 m Wcm^-2.3)A series of alternating D–A₁–D–A₂ copolymers were synthesized and characterized with oligothiophenes?n T,n=1,2,3?as the donor and two electron-deficient moieties,quinoxaline and isoindigo,as the acceptors in the repeating unit.The influence of the donor segments with different numbers of thiophene units and effect of the addition of fluorine to the quinoxaline unit of D–A₁–D–A₂ polymers were studied.It was found that increasing the length of the donor thiophene units,broader absorption spectra were observed in addition to a sequential increase in HOMO levels,while the LUMO levels displayed very small variations.The addition of fluorine to quinoxaline unit not only decreased the HOMO levels of the resulting polymers,but also enhanced the absorption coefficients.A superior photovoltaic performance was observed for the P3TQTI-F-based device with a power conversion efficiency?PCE?of 7.0%,a J_sc of 15.49 m A/cm²,a V_oc of 0.67 V and a FF of 67.4%.4)A vertical benzo[1,2-b:4,5-b']dithiophene-2,6-dicarboxylate?V-BDTC?with weak electron-withdrawing character was primarily developed.A series of wide band-gap?WBG?copolymers based on V-BDTC acceptor copolymerized with different donors were designed and synthesized.Their optical absorption,electrochemical property,film morphology,and solar cell performance were systematically investigated.It is found that the weak electron-withdrawing V-BDTC unit endows its copolymers with wide band gaps and deep HOMO energy levels.PV-BDTC2 exhibits a promising PCE of 7.49%with a high V_oc of 1.03 V in the solution-processing polymer solar cells?PSCs?.5)Two kinds of asymmetric donors of indeno[1,2-b]thiophene?IT?and thieno[3,2-c]isochromene?TC?were devoleped.And a series of D-A-type polymers with asymmetric structures were synthesized basd on IT or TC donors,benzothiadiazole?BT?or fluorinated benzothiadiazole acceptor units,respectively.It is found that the IT based polymers have good solubility and high charge mobilities,while the TC based polymers exhibited wider absorption spectra and better molecular planarity.As a resuilt,the IT based polymer PIT2FBT?n-Do?showed higher power conversion efficiency of 9.23%with a higher open-circuit voltage(V_oc)of 0.90 V.On the other hand,the TC based polymer of PTC2FBT exhibited a maximum PCE of9.06%with a J_sc of 15.3 m A/cm² were obtained in PTC2FBT based PSCs without any post-treatment.