We find that conjugated polymers can undergo reversible structural phase transitions during electrochemical oxidation and ion injection.We study poly[2,5-bis(thiophenyl)-1,4-bis(2-(2-(2methoxyethoxy)ethoxy)ethoxy)benzene] (PB2T-TEG), a conjugated polymer with glycolated side chains. Using grazing incidence wide angle X-ray scattering (GIWAXS), we show that, in contrast to previously known polymers, this polymer switches between two structurally distinct crystalline phases associated with electrochemical oxidation/reduction in an aqueous electrolyte. Importantly, we show that this unique phase change behavior has important physical consequences for ion transport. Notably, using moving front experiments visualized by both optical microscopy and super-resolution photoinduced force microscopy (PiFM), we show that a propagating ion front in PB2T-TEG exhibits non-Fickian transport, retaining a sharp step-edge profile, in stark contrast to the Fickian diffusion more commonly observed. This structural phase transition is reminiscent of those accompanying ion uptake in inorganic materials like LiFePO 4 . We propose that engineering similar properties in future conjugated polymers may enable the realization of new materials with superior performance in electrochemical energy storage or neuromorphic memory applications.
A non-fullerene acceptor ITTIC is developed for polymer solar cells with a donor polymer PBDB-T1. A high PCE of 9.12% was obtained with an energy loss of 0.54 eV at a diminished donor/acceptor energy offset.
It is challenging yet appealing for researchers to construct new polymer donors that can work cooperatively with the polymer acceptors and thus realize maximum power conversion efficiencies (PCEs) of all-polymer solar cells (PSCs). We have synthesized two dithieno[3,2-f:2′,3′-h]quinoxaline-based wide band gap donor polymers (PBQx-Me-TF and PBQx-H-TF) and a new γ-position based narrow band gap polymer acceptor: PBTIC-γ-TT. The temperature-dependent absorption spectra showed that removal of a weaker electron-donating methyl group in the donor polymer strengthened the aggregation and the absorption coefficients. The crystal structures showed that PBQx-H-TF had a closer π−π stacking distance of 3.33 Å when compared to the PBQx-Me-TF (3.40 Å). The smaller E HOMO offset (0.07 eV) between the donor PBQx-H-TF and acceptor PBTIC-γ-TT than that of PBQx-Me-TF/PBTIC-γ-TT (0.10 eV) provided a better hole transport. The PBQx-H-TF/PBTIC-γ-TT films showed a smaller total energy loss (0.574 eV) than the PBQx-Me-TF/PBTIC-γ-TT film (0.607 eV); hence, this molecular structure adjustment reduced the nonradiative energy loss. PBQx-H-TF also showed better miscibility with PBTIC-γ-TT with a smaller χ value of 0.25. In addition, a bicontinuous interpenetrating microstructure was observed in the active layer blend film (PBQx-H-TF/PBTIC-γ-TT), resulting in a J SC of 22.24 mA cm −2 , a FF of 67.80%, and a PCE of 14.21% in the device. These observations revealed the significance of molecular structure adjustment for better device performance, and therefore, PBQx-H-TF can be an excellent candidate for all-PSCs.
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