2.2 The photocurrent response under polarized light
The single-component PBDB-TF and IT-4F were fabricated into the device. The polarized photocurrent tests are used to verify the effect of different stacking morphologies of molecules on the response of the device under polarized light. Figure S2a and S2c are the photocurrent curves of PBDB-TF and IT-4F obtained by adding 1/2 wave plate separately. It can be seen that the photocurrent signal of PBDB-TF changes periodically with the polarization angle of the 1/2 wave plate. However, the photocurrent signal of IT-4F does not change periodically. The single attenuation trend of the signal is caused by the intensified phase separation of small organic molecules under illumination. These results are similar to those obtained by GIWAXS spectra. And the films are anisotropic due to the ordered arrangement of the donor PBDB-TF, while the IT-4F films are isotropic due to the random orientation. After adjusting the angle of the 1/2 wave plate, a 1/4 wave plate is added to study the difference between the linearly and the circularly polarized photocurrent. As shown in Figure S2b and S2d, it is worth noting that the linearly polarized photocurrent of single-component PBDB-TF is larger than the circularly polarized photocurrent. In contrast, the photocurrent generated by IT-4F under differently polarized light is hard to observe.
Generally, the active layer thin films in OSCs are optically isotropic[21] because the active layer is usually a bulk heterojunction. When changing the incident azimuth angle, however, it is found that the photocurrent signal changes with the variation of incident angles, as shown in Figure 2 a. To further verify whether the thin film has anisotropy, we tested it by changing the azimuth angle of the sample in Figure 2b. The sample shows an anisotropy axis through the above two-step experiments.