Figure3. (a) Photocurrent measured by switching phase angle
with different laser power. (b) The relationship of PC and ∆PC with
different laser power. (c) Photocurrent measured by switching phase
angles with different applied voltages. (d) Linearly and circularly
polarized photocurrents in magnetic fields vary with the magnetic field.
The symbol arrow and circular arrow represents the linearly and
circularly polarized light.
Based on the anisotropy analysis of the thin organic film, we tested the
polarized photocurrent to study the photoelectric process of the excited
state of the active layer in OSCs. As shown in Figure 3 a, the
photocurrent signal of the sample changes periodically with the angle of
the 1/4 wave plate. The variation of photocurrent has the same trend in
the power range from 0.2 mW to 2.6 mW. Compared with linearly polarized
light excitation, the signal could be attenuated to a certain extent
under circularly polarized light excitation. To quantitatively compare
the difference between the linearly polarized photocurrent and the
circularly polarized photocurrent, we define PC as the average
photocurrent, ΔPC as the difference between the linearly polarized
photocurrent and the circularly polarized photocurrent, PC(L) as the
linearly polarized photocurrent, PC(C) as the circularly polarized
photocurrent. Then we extract the variation trends of PC and △PC with
light intensity. As shown in Figure 3b, PC shows an increasing linear
trend with the rise of optical power. At higher optical power density,
the photocurrent saturation is gradually saturated. This is because the
increase of the optical power density enhances the exciton generation
rate, thus generating more excited states. After the excited state is
saturated, the photocurrent also tends to saturate.