P3HT blended with different fullerene derivatives (PC60BM, PC61BM, PC70BM and PC71BM) have
been prepared and studied as active layers in organic solar cells (OSCs). These PCBM have different LUMO and
HOMO positions which subsequently influence the PV parameters of the OSCs such as open circuit voltage (Voc) and
the built-in potential (Vbi). Charge carrier mobility is found to vary with the type of fullerene used with maximum
value of 9.3 x10-6 cm2V-1s-1 for the P3HT:PC61BM based device. The latter has exhibited the highest device
performance with power conversion efficiency (PCE) reaching 4.2% corresponding to a fill factor (FF) of 62%, with
open circuit voltage (Voc) of 0.65V and short circuit current density (Jsc) of 10.4 mA.cm-2. The improved fill factor
has been attributed to the lower series resistance (Rs) in the studied devices.