Figure 1. (a) The schematic diagram of the molecular structures of PBDB-TF and IF-4F. (b) SEM image of the device cross-section. GIWAXS spectra of (c) PBDB-TF, (d) IT-4F, (e) PBDB-TF:IT-4F films. (f) The Raman intensity in wavenumber 1430 cm-1 with different polarized angles.
To gain a deep understanding of the effect of polarized light on device performance, it is necessary to investigate the morphology and anisotropy of the active layer. As shown in Figure 1c-e, we performed 2D-GIWAXS tests on PBDB-TF, IT-4F, and PBDB-TF:IT-4F films, respectively. For the single-component PBDB-TF, the characteristic peak (010) intensity is concentrated and has high crystallinity. At the same time, the π-π stacking is along the direction perpendicular to the substrate, forming a face-on orientation.[19]However, the single-component IT-4F has a ring-shaped scattering feature, indicating that the single IT-4F molecules are randomly oriented.[20] For the binary blend film, the orientation is similar to that of PBDB-TF, indicating that the alignment and orientation of organics are greatly affected by the polymer in the active layer of the prepared device. Meanwhile, the random packing of IT-4F molecules is suppressed, but the overall molecular stacking is still face-on, which is beneficial to the charge transport in the device.