Theoretical Study Of The Porphyrin Sensitizers SM315, GY50, FA And KS And The Co-sensitizer CDCA

The development and synthesis of novel dye sensitizers are important for improving power conversion efficiency of dye-sensitized solar cells(DSSCs)in terms of the role of dye sensitizers in photon to electricity energy conversion processes.How the different moieties tune the electronic structures and related properties is the fundamental issue of design dye sensitizer.Here,the geometries,electronic structures,excitation properties,and free energy variations for electron injection(EI)and dye regeneration(DR)of porphyrin dye sensitizers SM315,GY50,FA,and KS,containing bulky bis(2?,4?-bis(hexyloxy)-[1,1?-biphenyl]-4-yl)amine,diarylamino group with two hexyl chains,quinolizinoacridine and triazatruxene as electron donors,respectively,were calculated.The Q bands absorption spectra of FA and KS exhibit blue-shift relative to those of SM315 and GY50,resulting from weak conjugation effects.The transition configurations and MOs analysis suggest the electron donors in these dyes are effective chromophores for photon-induced EI in DSSCs.The torsion angle between electron-donor and conjugation-bridge has significant effects on electronic structures,excited states,charge transfer(CT)properties,and free energy variations for EI and DR.The transferred charges and CT distances demonstrate quinolizinoacridine in FA is the most prominent electron donor moiety among these porphyrin dyes.It is necessary to suppress recombination of charges,dye aggregation and dissociation,etc.to further enhance the photoelectric conversion efficiency and stability of the dye-sensitized solar cell using co-sensitizer,such as Chenodeoxycholic acid(CDCA).In this paper,the molecular structure of CDCA includes a carboxyl group and two hydroxyl groups,which distributes in the two ends of the molecule.The hydroxyl group can form a competitive adsorption with the dye molecule on the semiconductor surface.However,the carboxyl group is hydrophobic,which can prevent the semiconductor interface from contacting the electrolyte,thereby increasing the stability of the device.Through the density functional calculation of the electronic structure,the excited state and the absorption spectrum,the HOMO-LUMO gap of CDCA molecules is too large to be suitable as a sensitizer alone.Absorption spectroscopy shows that CDCA has no effect on the absorption of the battery.In addition,the excited state analysis of CDCA demonstrates that the main transition configuration is slow electron injection when it is adsorbed on the semiconductor surface as a co-sensitizer,which can effectively limit the dark current.