Design And Synthesis Of Ruthenium Complexes Sensitizers And Their Applications In Solar Cells

In recent years,the increasing demands for clean and sustainable energy make dye-sensitized solar cell(DSSC)a focus point for the global researchers.In the DSSC,the dye sensitizer and molecule monolayer on the surface of metal oxide semiconductor dominate the yield of light-harvesting,separated charges and the photon to current conversion efficiency.Up to now,ruthenium complex sensitizers remain the most widely investigated and used due to the broad absorption spectrum,high conversion effciency,appropriate energy levels and excellent stability.Developing the high performance ruthenium complex with broad absorption range,strong absorbance and appropriate energy levels is the starting point for this paper.In this work,by introducing the high delocalized electron-donating antennas onto the bipyridine ancillary ligands,we designed and synthesized four series of novel ruthenium complex sensitizers in accordance with the order of conjugation degree and length.The impacts of electron-donating antennas on the photophysical and electrochemical properties of ruthenium sensitizers and their behavior in DSSCs were evaluated and investigated carefully.Three heteroleptic ruthenium complexes,RC-15,RC-16 and RC-22,with sulfur-or oxygen-containing electron-donor,phenylpyridine-based ancillary ligands,were synthesized.The influence of the different electron donors-the acyclic electron donor methylthio and methoxyl,and the cyclic electron donor methylenedioxy-on the photophysical and electrochemical behavior in dye sensitizers and photovoltaic performance in DSSCs were investigated.Owing to the cyclic nature of its electron-donor ancillary ligand,RC-22 shows the highest absorption intensity compared to RC-15 and RC-16,and therefore,it is likely to exhibit the highest short circuit photocurrent density(Jsc),which is confirmed from the IPCE values(90%)in following sections.Arylamine derivatives,which contain many favorable photoelectrochemical behaviors,are good candidates for the electron-donating antennas applied in the molecule design of ruthenium dye sensitizers in DSSCs.Furthermore,arylamine electron-donating antennas can provide the polarity matching between the polar ruthenium sensitizer and the nonpolar holeconductor,thus improving interfacial contact,which is significant for enhancing the photovoltaic performance.In this work,to make a systematic research about the role of arylamine electron-donating antennas on the ruthenium sensitizers and the solar cells,we designed and synthesized three heteroleptic ruthenium sensitizers(coded as RC-31,RC-32 and RC-36)featuring organized arylamine electron-donating antennas(N,N-diethyl-aniline,julolidine group and N,N-dibenzyl-aniline)on bipyridyl ancillary ligands.Among three RC sensitizers,N,N-dibenzyl-aniline in RC-36 was found to be the most desired candidates which could tune the dyes' structural-electronic nature and lead to notable enhancement in the light harvesting capacity.The corresponding DSSC achieved impressive power conversion efficiency of 10.23%.The poor performance of the RC-32 sensitized device(7.43%)was attributed to shallow HOMO level which caused by the nature of julolidine electron-donating group and inefficient dye regeneration process.To develop efficient electron-donating antennas,we present an investigation on the synthesis,photophysical,electrochemical properties,and solar cell performances of three meticulously designed ruthenium complex sensitizers,coded as RC-41,RC-42,and RC-43.For for the RC-41 dye,phenylcarbazol,a new electrondonating antenna which has similar structure with TPA,is introduced into the bipyridine ligand.In the structure of RC-42 dye,a stronger electron-donating antenna-methoxy-triphenylamine(MeO-TPA)is attached to the bipyridine ligand.To further improve the electron donating ability and extend conjugation length of the ancillary bipyridine ligand in RC-42,ethylene-dioxythiophene(EDOT)is employed as the spacer between the MeO-TPA and bipyridine unit in the case of RC-43 dye.The DSSCs based on RC-43 dye obtained the most impressive power conversion efficiency with 10.78%.With the purpose of exploring the further insight into the evolution of ruthenium terpyridyl sensitizers,a series of ruthenium terpyridyl complexes(RC-T51,RC-T52 and RC-T53)modified with three different electron-donating ancillary bipyridine ligands were molecularly synthesized and employed as dye sensitizers for DSSCs.All these dyes contain the 4,4',4"-tricarboxylic-2,2':6',2"-terpyridine ligand acting as an anchoring ligand for effective bonding.The only existed NCS group can adjusts the properties of the ruthenium metal center by destabilizing the ruthenium metal t2g orbital.Compared with N749,the relatively inferior performance of RC dyes were ascribed to the improper delocalization of the HOMO energy level and the inefficient dye generation process.The molecule engineering strategy offers an alternative route for the construction of more efficient and stable ruthenium terpyridyl complexes sensitizers.