We report an analysis of the ac response of a bulk-heterojunction solar cell in a standard architecture
made of an anthracene containing poly(p-arylene-ethynylene)-alt-poly(p-arylene-vinylene)/1-(3
methoxy carbonyl) propyl-1-phenyl[6,6] and C60 (AnE-PVstat:PCBM) blend, these were made in detail
at room temperature. Impedance spectroscopy is showing “backwards” arcs in Cole–Cole
figures at low frequencies that are interpreted through equivalent circuit using negative resistances for electrical
contacts. This equivalent circuit model incorporated chemical capacitance (Cm), recombination resistance
(Rrec), transport resistance (Rt) and contact electrical resistance (Rco). We have taken Rco as negative
values in the bipolar regime to theoretically reproduce the small arc shown in the Nyquist plots. In
addition, negative capacitance (NC) was observed under positive dc biases in the bipolar regime. The
recombination time trecdecreases with increasing bias voltages. This result is in agreement with the
direct Langevin-type bimolecular recombination. We determined the diffusion time (tdif ) and the
diffusion length (Ln) and other parameters. Average mobility of global carriers for the device is around
4103cm2 V1 s1 which is in good agreement with that derived using PCBM electron-only devices.