Intrinsic Delocalization During The Decay Of Excitons And Electric-field-induced Breaking Of Carrier Fusion In Conjugated Polymers

Conjugated polymer materials are widely used in polymer solar cells.Recent years,scientists have worked on improving the efficiency of organic solar cells.This thesis focuses on two aspects:1.Intrinsic delocalization during the Decay of Excitons;2.Electric-field-induced breaking of carrier fusion.Under photoexcitation,the electron transition rapidly forms the electron-hole pair,and then form a singlet exciton after the relaxation process.Based on the developed nonadiabatic fluorescence dynamics,during the decay of exciton,the dipole moment drives the electron to partially transfer to extended orbitals from the original localized ones,leading to self-delocalization.Based on the dynamic fluorescence spectra,the delocalization of excitons is revealed to be an intrinsic property dominated by exciton decay,acting as a bridge for the exciton to diffuse in the polymeric solar cell.The modification of the dipole moment enhances the efficiency of polymer solar cells.When an electric field is applied to polymeric solar cells,the external electric field has a large influence on the transfer of charged carriers in bulk polymer.When the external electric field intensity is less than 5.5×104V/CIm,the polaron approaches and collides with the exciton,it is easily trapped by the potential well produced by the exciton andthen forms a charged exciton.When the external field surpasses the threshold value of5.5×104 V/cm,the charged polaron absorbs momentum from the external electric field and shakes off the trapping of the exciton.It finally steps out of the original lattice potential well,where the appropriate electric field magnitude ranges from 5.5×104 V/cm to 8×105 V/cm.Then,the originally carriers is dissociated when the electric field reaches 0.8 MV/cm.So a surface electric field on the polymer solar cell can restrain the recombination of the resultant charged carriers and effectively keep the excitons from fusion with the transporting charged polarons.This provides a valid and easily manufactured approach to yield higher efficiency of polymer solar cells.