Polaron Confinement in n-Doped P(NDI2OD-T2) Unveiled by Vibrational Spectroscopy

Abstract

Through specific marker bands, IR and Raman spectra of chemically doped polyconjugated polymers allow investigation of doping and monitoring of its effectiveness. The vibrational modes associated with the doping-induced features provide information about the polymer units affected by the transferred charge and the structure relaxation associated with the formation of the polaron. Here, we doped the P(NDI2OD-T2) copolymer with three differently substituted 1H-benzimidazoles, which allow for doping in solution, leading to an increase of conductivity values up to four orders of magnitude. Careful inspection of the IR and Raman spectra of P(NDI2OD-T2) while varying the dopant concentration and the kind of dopant proves that the polaron markers are almost independent from the dopant species. The IR intensity of the polaron markers is a very sensitive probe of charge delocalization upon doping: for n-doped P(NDI2OD-T2), these bands show absorption intensities of the same strength as those of the pristine species. In other words, they are very weak in comparison to the so-called IRAV bands of doped polyacetylene, polythiophenes, and related materials. This experimental observation provides evidence of the strong confinement of the polaron on the NDI2OD unit. Multiwavelength Raman spectra of n-doped P(NDIOD-T2) further corroborate this point, showing that the T2 moiety is almost unaffected by doping. The analysis of the experimental data is complemented by DFT calculations which fully support the diagnosis of the formation of localized polarons. Hence, vibrational spectroscopy is an effective tool to characterize charge carriers induced by doping P(NDIOD-T2): it indicates that the observed conductivity enhancement is ascribed to an efficient interchain hopping involving charged NDI2OD units, whereas polaron diffusion along the chain is unlikely.

N-Doping improves charge transport and morphology in the organic non-fullerene acceptor O-IDTBR

“…Finally, we find that N-DMBI only acts as an n-dopant when it loses an H-atom and transfers a hydrogen anion to the O-IDTBR (Figure 4c), following the hydride transfer mechanism described previously. 21,44 However, we do note that, although the findings in our DFT results are substantiated throughout the literature, there are more recent, spectroscopic findings that exclude hydride transfer as a doping mechanism for N-DMBI-based systems, and rather support mechanisms of electron transfer between an electron acceptor and a donor 45 . Overall, the DFT results show the three dopants appear to n-dope the O-IDTBR via different mechanisms, with each dopant altering the electronic structure of O-IDTBR differently.…”

Mixed Conduction in an N‐Type Organic Semiconductor in the Absence of Hydrophilic Side‐Chains

“…While such order is beneficial for charge transport in undoped field effect devices, [ 43 ] the degree of charge carrier localization likely inhibits intra‐chain transport down the backbone that would benefit from this extended order. [ 44 ] This is opposed to BBL which shows evidence of delocalized charge carriers. [ 31 ]…”

High‐Performance, Flexible NO2 Chemiresistors Achieved by Design of Imine‐Incorporated n‐Type Conjugated Polymers

“…Before NO 2 exposure, IM‐0.3/P‐0.4 represented similar spectra with those of conventional NDI‐based CPs, reported in the previous literature. [ 59 ] An additional peak at ≈1574 cm –1 was observed from the intensity of C=N stretching vibrations. [ 60 ] After NO 2 exposure, the band from C=N stretching was decreased and the overall Raman spectra exhibited upward shifts (≈6.5 cm −1 ).…”