Interplay between Intrachain and Interchain Excited States in Donor–Acceptor Copolymers

Abstract

Recently, rapid progress in the power conversion efficiency for organic solar cells (OSCs) is achieved due to the phenomenal development of the nonfullerene electron acceptors. In addition to the pairing electron donors, conjugated donor–acceptor copolymers are another key player in the high-efficiency OSCs. Here, the temporal evolution of excited states in a typical copolymer, PM6, was traced by transient absorption spectroscopy. The spectroscopic result implies the formation of two kinetically correlated intrachain species, polaron excitons and intrachain polaron pairs. In the presence of the interchain interaction, these intrachain species quickly convert into interchain polaron pairs on a time scale of few picoseconds. Our findings reveal that the electron transfer mechanisms in PM6-based OSCs substantially depend on the PM6 environment in the bulk heterojunction blends.

Red-Light-Mediated Photocatalytic Hydrogen Evolution by Hole Transfer from Non-Fullerene Acceptor Y6

“…In PM6 films, a decrease in SE has been attributed to the formation of non-emissive species, including interchain and intrachain polaron pairs. 45,46 Our data are consistent with the presence of these species in PM6 NPs. The GSB kinetics at 571 nm fit to a bi-exponential decay with time constants τ 1 = 89.2 ± 0.8 ps and τ 2 = 2.82 ± 0.06 ns (Supporting Information, Section 7.2).…”

“…This feature has a dip around 700 nm to 750 nm, which is lost over ∼200 ps as the ESA broadens. This dip in the ESA has previously been attributed to the overlap of the broad ESA with the (negative) stimulated emission (SE) of PM6, 45,46 as PM6 is emissive in this region (Figure S3). In PM6 films, a decrease in SE has been attributed to the formation of non-emissive species, including interchain and intrachain polaron pairs.…”

“…TA spectra of the neat PM6 NPs (Figure 5a) broadly resemble TA spectra of PM6 films. 18,19,29,[44][45][46] The spectra exhibit a strong ground-state bleach (GSB) in the 500-650 nm region, with two peaks that correspond to the peaks in the steady state absorption of these NPs (Figure 2b). At early times, an excited-state absorption (ESA) appears from 650 nm to 780nm, which is attributed to the absorption of PM6 excitons.…”

Ternary‐Assisted Sequential Solution Deposition Enables Efficient All‐Polymer Solar Cells with Tailored Vertical‐Phase Distribution

“…As depicted in Figure S10 (Supporting Information), ternary SSD film has a faster decay process (16.2 ps) at 1280 nm than neat PY-IT film (28.2 ps), which indicates that the HT process from PY-IT to PM6 is triggered by the photo-excited iPPs. [36,37] Figure 3c illustrates the HT process that excitons in PY-IT are generated immediately after excitation and transferred to the iPP-mediated HT state within 0.1 ps. The dynamics were probed at 720 and 1280 nm, respectively.…”

Computational characterization of charge transport resiliency in molecular solids

“…This is approximately based on considerations of overlap integrals as discussed in several earlier studies. [34][35][36][37][38] We next augment this initial weight distribution (that differentiates between inter-and intrachain edges), with a more detailed weight distribution that accounts for (a) rotation between neighboring monomers within a chain, (b) the distance and degree (and associated electronic couplings) of geometric slip between monomers on two chains, and (c) the direction of the applied electric field. Intermonomer units along a chain (intrachain) are modified as a function of the rotation between the units, as planar conformations give rise to larger transfer integrals than orthogonal conformations.…”