Synthesis And Performance Studies Of Novel Carbazole Dyes Based On Donor Planarization Engineering

In recent years,dye-sensitized solar cells（DSSCs）are widely studied due to their low cost,easy manufacture,and high photoelectric conversion efficiency.One of the most important components is sensitizer.As the critical property of the organic dye,the energy level determines the thermodynamic possibility and the efficiency of interfacial charge transfer processes in DSSCs.Therefore,the energy level is an important factor that limits the photovoltaic performance of dyes.With the continuous development of organic dyes,selective energy level control becomes a quite important and systematic project.In this paper,four new D-A-π-A type carbazole dyes are designed and synthesized.By simple aryl immobilization,the dihedral angle between benzene and carbazole is sharply decreased with the molecular planarity optimized and its performance is studied in detail.In chapter 1,we briefly describe the development prospects of dye-sensitized solar cells（DSSCs）,characteristics and classification,and some organic dyes with carbazole as donor are summarized in recent years.Finally,the design idea of this paper is introduced:selectively energy control of the dyes through planarization.In Chapter 2,with carbazole as donor,benzothiadiazole as auxiliary acceptor,and benzoic acid as acceptor,two dyes CS-14 and CS-15 are synthesized by changing the planarity between carbazole and benzene units.The structures of the compounds are characterized by ¹H NMR and ¹³C NMR.The properties,including photophysical electrochemistry and photovoltaic performance are further studied.Along with the improvement of planarity at donor segment,the HOMO level of the dye lifts effectively,and more important,its LUMO level remains around the same value.Therefore,CS-15 exhibits the best photovoltaic performance which is J_SC=15.31 mA cm^-2,V_OC=741 mV,ff=0.685,η=7.77%.In chapter 3,with similar donors and acceptorsas used in chapter 2,dyes CS-16 and CS-17 are synthesized.The structures of the compounds are characterized by ¹H NMR and ¹³C NMR.The properties,including photophysical electrochemistry and photovoltaic performance are further studied.It is found that the dye CS-17 synthesized by aryl immobilization showed that along with the improvement of planarity at donor segment,the HOMO level of the dye also lifts effectively,and more important,its LUMO level also remains around the same value.So CS-17 exhibits the best photovoltaic performance which is J_SC=14.77 mA cm^-2,V_OC=724 mV,ff=0.667,η=7.13%.Moreover,in the synthesis of intermediate 6’of CS-17,two isomers appear due to the asymmetry of the molecules,which are characterized by ¹H NMR.The mechanism of the cyclization process is studied by theoretical calculation.In chapter 4,the conclusions are presented.The n-octyloxy-substituted carbazole is synthesized by a series of reactions such as Suzuki coupling and free radical substitution reaction,and a series of dyes CS-14-CS-17 is synthesized as donor.It is found that excellent planarity of donor segment selectively lifts the HOMO energy level and is obviously preferred to improve multiple interfacial charge transfer efficiencies,and the photovoltaic performance of the battery device through the study of photovoltaic performance,supplemented theoretical calculation.