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.