Polaron spin echo envelope modulations in an organic semiconducting polymer

Abstract

Theoretical treatment of the electron spin echo envelope modulation (ESEEM) spectra from polarons in a semiconducting π-conjugated polymer is presented. The contact hyperfine coupling and the dipolar interaction between the polaron and proton spins are found to have distinct contributions in the ESEEM spectra. However, since the two contributions are spaced very closely, and the dipolar contribution is dominant, the detection of the contact hyperfine interaction is difficult. To resolve this problem, a recipe of probing the contact hyperfine and dipolar interactions selectively is proposed, and a method for detecting the polaron contact hyperfine interaction is formulated. The ESEEM decay due to the polaron random hopping is analyzed, and the robustness of the method against this decay is verified. Moreover, this decay is linked to the transport properties of polarons, providing an auxiliary probe for the polaron transport.

Ultra-fast spin-mixing in a diketopyrrolopyrrole monomer/fullerene blend charge transfer state

“…41 The mechanism for spinmixing has been proposed to involve hyperfine interactions between the polaron electron spin and the surrounding proton spins. 42 Hyperfine interactions are typically very weak, but can start to dominate when the two electron spins in the pair possess a large spatial separation, 43 and therefore strong hyperfine interactions may also play a role in the ultra-fast spin-mixing. It has also been noted that ISC can occur very efficiently between 1 CT and a close lying triplet level of a single component (donor or acceptor), 44,45 due to the spin flip coupling to a change in orbital angular momentum.…”

Enhancing the Photovoltaic Performance of Triplet Acceptors Enabled by Side‐Chain Engineering

“…The spin-spin (T 2 ) relaxation times were calculated to be 27.92, 27.98, and 27.94 ns for BT2-4Cl-, BT3-4Cl-, and BT4-4Cl-based films, respectively, suggesting a similar process of transverse magnetization decay, which may be due to the close spin-orbit coupling (SOC) effects among the three acceptors. [58] However, the spinlattice (T 1 ) relaxation times for BT2-4Cl-, BT3-4Cl-, and BT4-4Cl-based films were evaluated to be 49.9, 84.7, and 62.8 ns, respectively. The longest T 1 of BT3-4Cl-based blend film is a promising candidate for achieving a long spin diffusion length, [56] indicating a more efficient charge transport process, which is in line with the highest J sc value of BT3-4Cl-based photovoltaic devices.…”