2.1 Device characterization
The device structure used in the experiment is ITO/PEDOT:PSS/active layer/PFN-Br/Al and the active layer is PBDB-TF:IT-4F. Figure 1 a shows the molecular formula of PBDB-TF and IT-4F. As shown in Figure 1b, the SEM cross-sectional picture presents the thickness of each layer of the device. The favorable continuity of each layer reduces the leakage current in the device, which is necessary for the regular operation of the device. Figure S1a shows the J-V curve of the solar cell. The corresponding IPCE spectrum and the integrated current obtained by IPCE are given in Figure S1b. The short-circuit current density (Jsc) of the cell is 20.12 mA/cm2, and the obtained PCE can reach 13.12%.