Optimization of organic solar cells (OSCs) active layer thickness for improved performance has been
investigated for P3HT:PCBM hybrid bulk heterojunction OSCs. Active layers in the range 65-266 nm were produced
using a conventional device structure (ITO/PEDOT:PSS/P3HT:PCBM/Al). UV-visible absorption spectra revealed
typical P3HT:PCBM absorption features for all obtained thicknesses. The dark J-V characteristics were employed to
determine the charge carrier mobility using space charge limited conduction theory (SCLC) and series resistance of
investigated devices were also derived. Series resistance was found to decrease with decreasing active layer thickness
reaching lowest value of 33.9? for film thickness of 95nm. Furthermore, charge carrier mobility was found to
increase with decreasing thickness of the active layer, with a maximum mobility value of 1.37 ×10-5 cm2V-1s-1
obtained for the 95nm thick films. Measurements of the PV characteristics of the investigated devices have revealed
optimum performance when active layer thickness was 95 nm. Power conversion efficiency (PCE) as high as 3.86%,
fill factor (FF) of 50%, short circuit current (Jsc) of 12.6 mAcm-2 were achieved for optimum active layer thickness of
95nm. On the other hand open circuit voltage (Voc) remained almost unchanged in range of 0.61-0.62V for all
investigated devices. Moreover, device stability was shown to be largely improved for optimum active layer thickness
with constancy for more than three months.