In Situ Spectroscopic and Electrical Investigations of Ladder-type Conjugated Polymers Doped with Alkali Metals

Abstract

Ladder-type conjugated polymers exhibit a remarkable performance in (opto)electronic devices. Their double-stranded planar structure promotes an extended π-conjugation compared to inter-ring-twisted analogues, providing an excellent basis for exploring the effects of charge localization on polaron formation. Here, we investigated alkali-metal n-doping of the ladder-type conjugated polymer (polybenzimidazobenzophenanthroline) (BBL) through detailed in situ spectroscopic and electrical characterizations. Photoelectron spectroscopy and ultraviolet–visible–near-infrared (UV–vis–NIR) spectroscopy indicate polaron formation upon potassium (K) doping, which agrees well with theoretical predictions. The semiladder BBB displays a similar evolution in the valence band with the appearance of two new features below the Fermi level upon K-doping. Compared to BBL, distinct differences appear in the UV–vis–NIR spectra due to more localized polaronic states in BBB. The high conductivity (2 S cm –1 ) and low activation energy (44 meV) measured for K-doped BBL suggest disorder-free polaron transport. An even higher conductivity (37 S cm –1 ) is obtained by changing the dopant from K to lithium (Li). We attribute the enhanced conductivity to a decreased perturbation of the polymer nanostructure induced by the smaller Li ions. These results highlight the importance of polymer chain planarity and dopant size for the polaronic state in conjugated polymers.

Ground-state electron transfer in all-polymer donor:acceptor blends enables aqueous processing of water-insoluble conjugated polymers

“…2c, d ). Pristine BBL films exhibit two distinct peaks at 398.4 eV and 400.5 eV, corresponding to the two different nitrogen sites 49 . Pristine PCAT-K films show two peaks at 164.1 eV and 165.3 eV, related to the spin-split doublet of sulfur in the thiophene ring.…”

Charge Transfer in the P(g42T-T):BBL Organic Polymer Heterojunction Measured with Core-Hole Clock Spectroscopy

“…Thus, this peak increases when the relative amount of the donor is increased. The C 1s component at 288.6 eV, found mainly in the 10 and 50% donor samples, originates from the double bonded carbon and oxygen in BBL (CO) . The S 1s spectra display the opposite trend in intensity as the nitrogen spectra as sulfur is found only in the donor polymer.…”

“…The C 1s component at 288.6 eV, found mainly in the 10 and 50% donor samples, originates from the double bonded carbon and oxygen in BBL (C�O). 26 The S 1s spectra display the opposite trend in intensity as the nitrogen spectra as sulfur is found only in the donor polymer. One discrepancy from the intensity trend of the main sulfur peak at 2472.4 eV (S−C) is found in the 90% donor sample, which is lower than that of the 50% sample.…”

Ground-state electron transfer in all-polymer donor-acceptor blends enables aqueous processing of water-insoluble conjugated polymers

“…2c and 2d). Pristine BBL films exhibit two distinct peaks at 398.4 eV and 400.5 eV, which correspond to the two different nitrogen sites 39 .…”