Dependence of Exciton Diffusion Length and Diffusion Coefficient on Photophysical Parameters in Bulk Heterojunction Organic Solar Cells

Douglas Yeboah, Jai Singh

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    Abstract

    Recently, the dependence of exciton diffusion length (Formula presented.) on some photophysical parameters of organic solids has been experimentally demonstrated, however no systematic theoretical analysis of this phenomenon has been carried out. We have conducted a theoretical study by using the Förster resonance energy transfer and Dexter carrier transfer mechanisms together with the Einstein–Smoluchowski diffusion equation to derive analytical models for the diffusion lengths (Formula presented.) and diffusion coefficients (Formula presented.) of singlet (Formula presented.) and triplet (Formula presented.) excitons in organic solids as functions of spectral overlap integral (Formula presented.), photoluminescence (PL) quantum yield (Formula presented.), dipole moment (Formula presented.) and refractive index (Formula presented.) of the photoactive material. The exciton diffusion lengths and diffusion coefficients in some selected organic solids were calculated, and we found that the singlet exciton diffusion length (Formula presented.) increases with (Formula presented.) and J, and decreases with n. Also, the triplet exciton diffusion length (Formula presented.) increases with (Formula presented.) and decreases with (Formula presented.). These may be achieved through doping the organic solids into broad optical energy gap host materials as observed in previous experiments. The calculated exciton diffusion lengths are compared with experimental values and a reasonably good agreement is found between them. The results presented are expected to provide insight relevant to the synthesis of new organic solids for fabrication of bulk heterojunction organic solar cells characterized by better power conversion efficiency.

    Original languageEnglish
    Pages (from-to)6451-6460
    Number of pages10
    JournalJournal of Electronic Materials
    Volume46
    Issue number11
    DOIs
    Publication statusPublished - Nov 2017

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