Organic photovoltaic initial stage degradation analysis using impedance spectroscopy

• Initial stage degradation of organic solar cells has been investigated.
• Measurement in dark provided exact information of device layers and interfaces.
• The factors of the initial stages of device’s degradation were identified.
• The degradation of P3HT:PCBM layer indicates the device’s irreversible degradation.

Shelf lifetime of organic solar cells based on P3HT:PCBM has been investigated using high magnitude and phase resolution impedance spectrometer. From the traditional current–voltage degradation curve, several stages of changes causing the device performance degradation are discussed. Degradation process of the devices has been monitored using impedance spectrometer under light, and dynamic parameters changes have been derived by model fitting, which are unable to provide information regarding the different stages of device changes though. However, layer analysis tested using impedance spectrometer in dark, provided exact information of device’s layers and interfaces changes during degradation process. Higher capacitance at PEDOT-ITO interface and higher resistance at PEDOT-P3HT interface, and PEDOT bulk layer’s performance fluctuations contributed to the beginning stages of device degradation. The degradation of P3HT:PCBM layer indicates the starting of the final device irreversible degradation.