Photoinduced Injection Enhancement in Fullerene-Based Organic Solar Cell Originates from Exciton–Electron Interaction

The dependence of photocurrent of a typical copper phthalocyanine (CuPc)/C60 device on external negative bias under monochromatic light illumination is reported. With increase of the negative bias, the photocurrent originating from excitons in the CuPc layer is quickly saturated. On the contrary, the photocurrent originating from excitons in C60 layer does not reach saturation but increases continuously with negative bias. This abnormal enhancement shows that the behavior of excitons in C60 layer is completely different from that in the typical donor material CuPc. The triplet exciton–electron interaction in C60 is supposed to cause the photoinduced hole injection enhancement from cathode, resulting in the observed phenomenon. More experiments designed have confirmed this mechanism.