Impedance spectroscopy on degradation analysis of polymer/fullerene solar cells

•Impedance spectroscopy is applied to investigate degradation in PEDOT:PSS/Al device.•Nyquist plot analysis verifies the growth of harmful Al2O3 layer at blend/Al interface.•Al2O3 causes an increased Rrec across interface and decreases capacitance.•Increase in diffusion and recombination time constants is observed. Here we have presented degradation studies of ITO/PEDOT:PSS/P3HT:PCBM/Al based organic solar cell devices by employing impedance measurements under dark and illumination with storage time. The results of the study have been presented to understand the stability issues in such devices in view of the presence of unstable P3HT:PCBM/Al interface and more specifically due to the possible formation of Aluminum oxide (Al2O3) layer which grows with time. A typical time dependent Nyquist plots have been modeled with Gracia- Belmonte series based equivalent circuit model and analyzed to extract parameters such as a set of resistors, capacitors and a constant phase element. Theses parameters have been shown to be associated with the time dependent changes at the blend/Al interface.