A building-block approach to the development of an equivalent circuit model for organic photovoltaic cells

A novel approach to equivalent circuit modelling of organic photovoltaic (OPV) cells capable of simulating both optimal and degraded devices has been developed. Freshly made OPVs (composed of an active layer with a blended poly (3-hexylthiophene) (P3HT) and indene-C60 bisadduct (ICBA) film), that exhibit a characteristic 'J' shaped current-voltage (I-V) curve both in the dark and under illumination, are typically fitted to a one-diode equivalent circuit model. However, as device performance deteriorates, the I-V curve undergoes a series of changes resulting in the evolution of an 'S' shaped I-V curve, for which there is no widely accepted equivalent circuit model. Here we present a building-block approach to develop a simple equivalent circuit model which provides an excellent fit to experimental I-V data spanning the continuum from the ideal 'J' to degraded 'S' shaped curves. Applying this new model to P3HT:ICBA devices provides insights into the physical processes that occur during degradation.