Influence of cathode in organic solar cells performance

Abstract

In this work we have fabricated and characterized organic solar cells (OSC) based on blends of polyhexylthiophene (P3HT) and [6,6]-phenil-C61-butyric acid methyl ester (PCBM) with two different cathodes: Al and LiF/Al. Current- Voltage (I-V) curves under illumination have been measured and fitted with the standard equivalent circuit in order to extract circuital parameters, such as series and parallel resistances (Rs and Rp) ideality factor (n) and inverse saturation current (I0). The introduction of a thin layer (0.5 nm) of LiF between active layer and Al increases the open circuit voltage (Voc) but slightly reduces short current (Isc) and fill factor (FF). The overall result is a slight increase of the efficiency, from 2.53 % to 2.57 %. Circuital parameters have been extracted with two methods (approximated an exact), and results show that structures with LiF layer have lower parasitic effects (lower Rs and higher Rp).