Abstract
In bulk heterojunction polymer solar cells, external photoexcitation results in localized excitons in the polymer chain. After hot exciton formation and subsequent relaxation, 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.
Highlights
For two decades, scientists have worked on improving the efficiency of organic solar cells [1,2,3,4,5,6,7,8,9], where, in particular, there has been great progress in the application of semiconducting conjugated polymers in this field [4,5,8,10]
Based on the developed nonadiabatic fluorescence dynamics combined with electronic transition molecular dynamics, we aim to precisely depict the whole process of exciton radiative decay and its delocalization, as well as its corresponding dynamic fluorescence spectra, and to unveil the intrinsic delocalization channel, which acts as bridge for exciton diffusion in solar cells
After about the dipole moment drives the electron to partially toextended several extended orbitals ps,100 theps, dipole moment drives the electron to partially transfer transfer to several orbitals from the about ps, the dipole moment drives the electron to partially transfer to several extended orbitals from the original localized ones, leading to self-delocalization
Summary
Scientists have worked on improving the efficiency of organic solar cells [1,2,3,4,5,6,7,8,9], where, in particular, there has been great progress in the application of semiconducting conjugated polymers in this field [4,5,8,10]. Once the photoactive layer undergoes photoexcitation, aside from charge generation and singlet fission in organic solar cells, it mostly results in an electron–hole pair or an exciton. The fabricated heterojunction dissociates the exciton, and the resultant charge carriers freely move towards the cathode and anode. Reducing the length of exciton diffusion is desirable to cut down on exciton decay, and to improve the efficiency of the organic solar cell. On the basis of this structure, the mechanism regarding exciton diffusion can be briefly depicted: once an exciton or electron–hole pair is formed in an organic solar cell due to photoexcitation, the heterojunctions randomly distributed all over the bulk of solar cells largely reduce the exciton’s diffusion length, making it easy for the exciton to transfer and reach the heterojunction, eventually being separated into charged carriers at the interface
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