Influence of Molecular Shape on Solid-State Packing in Disordered PC₆₁BM and PC₇₁BM Fullerenes

Abstract

Molecular and polymer packings in pure and mixed domains and at interfacial regions play an important role in the photoconversion processes occurring within bulk heterojunction organic solar cells (OSCs). Here, molecular dynamics simulations are used to investigate molecular packing in disordered (amorphous) phenyl-C70-butyric acid-methyl ester (PC71BM) and its C60 analogue (PC61BM), the two most widely used molecular-based electron-accepting materials in OSCs. The more ellipsoidal character of PC71BM leads to different molecular packings and phase transitions when compared to the more spherical PC61BM. Though electronic structure calculations indicate that the average intermolecular electronic couplings are comparable for the two systems, the electronic couplings as a function of orientation reveal important variations. Overall, this work highlights a series of intrinsic differences between PC71BM and PC61BM that should be considered for a detailed interpretation and modeling of the photoconversion process in OSCs where these materials are used.

Closely packed, low reorganization energy π-extended postfullerene acceptors for efficient polymer solar cells

“…Finally, all electronic couplings have the same sign, which is reported (45) to be an important factor in achieving high mobilities. For comparison, ITIC has a greatest jJj value of 16 meV (SI Appendix, Table S7), crystalline PC 61 BM has been reported to have jJj values as high as 50 meV (46,47), and amorphous PC 61 BM and PC 71 BM are computed to have average jJjs of ∼12 meV (48). In summary, the combination of low reorganization energies and close π−π stacking of the LUMOlocalized terminal naphthyl groups leading to high electronic couplings is encouraging for future studies of ITN-C9 and, particularly, of ITzN-C9, where the electronic coupling distribution suggests a high charge transport dimensionality in crystalline domains.…”

Toward High‐Temperature Stability of PTB7‐Based Bulk Heterojunction Solar Cells: Impact of Fullerene Size and Solvent Additive

“…These values are in good agreement with experimental data from literature. [53] In order to study the enthalpy of mixing at different concentrations and to explore the possible morphologies of the blends, we generated ≈100 systems formed by PTB7 and PC 60 BM (or PC 70 BM) molecules, with varying numbers of fullerenes and varying initial dispositions within the polymer. The systems were carefully equilibrated by 10 ns long constant pressure and constant temperature annealing (NPT) at room conditions, during which anisotropic volume fluctuations were allowed.…”

Molecular-Scale Understanding of Cohesion and Fracture in P3HT:Fullerene Blends

“…Electron-acceptor materials derived from fullerenes -and in particular the phenyl butyric acid methyl ester substituted C 60 and C 70 derivatives (PC 61 BM and PC 71 BM, respectively), among a multitude of others [23][24][25][26] continue to dominate the BHJ OPV literature. However, it is not clear 4 how the chemical substitution patterns of the solubilizing groups influence the electronic and mechanical properties of these composite materials, as there remain many intricate details that need to be unfurled at the molecular-and nano-scales.…”