Interfacial charging originated from the conductivity decrease of C60 layer in IZO/pentacene/C60/Al organic double-layer solar cells

•EFISHG showed charging at both pentacene/C60 and inverted C60/pentacene OSCs.•Degradation of C60 layer can be the origin of interfacial charges in the OSCs.•The interfacial charge accumulation caused low I–V performance of inverted OSCs.

The origin of interfacial charging process in double-layer organic solar cells (OSCs) was studied by using the normal structure of Indium–Zinc–Oxide/pentacene/C60/Al and its inverted double-layer system. Optical electric-field-induced second-harmonic generation (EFISHG) measurement was employed and results suggested that interfacial charging in these two kinds of OSCs led to charge accumulation with opposite charge polarity, owing to the conductivity decrease of C60 layer. Applying the EFISHG measurements to the inverted OSCs also showed that the significant charge accumulation on donor–acceptor interface is responsible for the low I–V performance of the inverted OSCs. Thus, Maxwell–Wagner type interfacial charging, which is governed by the conductivity of C60, can cause the degradation of the I–V performance of OSCs. The protection of C60 layer from the conductivity decrease is a way to improve OSCs performance.

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