Study of multiple photovoltaic processes in stacked organic active layers

• The EFISHG experiments observed multi PV effects happened in different time domain.
• The multiple PV effects generate internal electric fields with opposite direction.
• The light degradation changes the relaxation time and the intensity of these fields.

By using optical electric-field-induced second-harmonic generation (EFISHG) measurement, we studied multiple photovoltaic (PV) effects which exist in multi-layer devices consisting of multiple pentacene and C60 layers stacked together in various sequence. Results verified that the photovoltaic effects happen on every donor–acceptor (DA) interface and induce multiple electric fields inside the devices. Meanwhile, the light degradation in film thickness direction changes the intensity and the relaxation time of the established internal electric fields. For the multi-layer devices with more than one DA interface, the internal electric fields with opposite directions always co-exist, which leads to suppress the total photovoltaic effect. Finally, we showed that the interaction between different internal electric fields is inhibited by decreasing the charge accumulation inside the organic active layer and thus the total PV effect of the device can be enhanced.

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