Two-peak capacitance–voltage behavior in devices based on electron transport materials

•Two peaks are observed in the C–V characteristics of fullerene based devices.•The origins of these two peaks show the same as those of hole-transport devices.•One C–V peak location shifts to negative bias when the buffer layer is thicker.•The related TPV signals show a polarity reversal of the internal electric field.•Such C–V peak returns to positive bias with an even thicker buffer layer.

Two peaks are observed in the capacitance–voltage (C–V) characteristics of electron-transport fullerene (C60 or C70)/Bphen based devices. The experimental results suggest that the mobile carriers generated from unintentional doping and trapped carriers are the origins of these two peaks, just the same as those of hole-transport devices. In addition, the polarity of one C–V peak voltage (the voltage corresponding to the peak capacitance) reverses as the Bphen layer thickness increases. The transient photo-voltage (TPV) signals show a polarity reversal of the internal electric field, confirming the related phenomenon.

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