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.