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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 dithieno3,2-f:2′,3′-hquinoxaline-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 EHOMO 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 JSC 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.
Zhao et al. (Fri,) studied this question.