Acceptor-Enhanced Local Order in Conjugated Polymer Films

Abstract

Disorder in conjugated polymers is a general drawback that limits their use in organic electronics. We show that an archetypical conjugated polymer, MEH-PPV, enhances its local structural and electronic order upon addition of an electronic acceptor, trinitrofluorenone (TNF). First, acceptor addition in MEH-PPV results in a highly structured XRD pattern characteristic for semicrystalline conjugated polymers. Second, the surface roughness of the MEH-PPV films increases upon small acceptor addition, implying formation of crystalline nanodomains. Third, the low-frequency Raman features of the polymer are narrowed upon TNF addition and indicate decreased inhomogeneous broadening. Finally, the photoinduced absorption and surface photovoltage spectroscopy data show that photoexcited and dark polymer intragap electronic states assigned to deep defects disappear in the blend. We relate the enhanced order to formation of a charge-transfer complex between MEH-PPV and TNF in the electronic ground state. These findings may be of high importance to control structural properties as they demonstrate an approach to increasing the order of a conjugated polymer by using an acceptor additive.

Charge Transfer Dynamics in Donor–Acceptor Complexes between a Conjugated Polymer and Fluorene Acceptors

“…6) becomes irrelevant and therefore the recombination rates approach the exponential behavior (Figure 7b). Most probably, the previously observed self-organization of the polymer chains in crystalline domains due to the CTC formation 14 adds another dimension to this scenario; a more detailed investigation on this issue is underway. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Visible-IR PIA spectroscopy has been further employed to study excited-state charge separation and recombination dynamics.…”

Role of Polymer Structure on the Conductivity of N‐Doped Polymers

“…Previous studies have indicated that dopant intercalation between polymer π-π stacking planes can account for similar q xy oriented refl ections in doped PBTTT and MEH-PPV. [ 16,40 ] The short d -spacing of these q xy oriented (010) peaks may be attributed to the small size of the dopants and the strong coulombic attraction between the polymer and dopant ions. Moreover, it is not clear what fraction of each of the polymers forms the phase responsible for the in-plane (010) refl ections.…”

Charge‐Transfer Complexes of Conjugated Polymers

“…Because CTC formation results in polymer chain planarization (see above), these domains can include ordered (aligned) polymer chains. In fact, domains of ordered polymer chains were observed in MEH‐PPV : TNF films,61 which are discussed in Section 4.2.…”

“…Recent X‐ray diffraction studies on MEH‐PPV : TNF blend films revealed that CTC formation could increase the film structural and electronic order 61. Figure 15 presents grazing‐incidence X‐ray diffraction (GIXD) data for pristine MEH‐PPV and 1 : 0.3 and 1 : 1 MEH‐PPV : TNF blend films 61. One can see that the neat MEH‐PPV film shows no clear diffraction features, but a uniformly decreasing scattering signal that reflects the amorphous film structure.…”