The thickness of active layer dependence of polymer solar cells

We studied the active layer thickness dependence of device performance of bulk heterojunction solar cells. The polymer solar cells comprising RR-P3HT:PCBM (1:0.8 (wt %:wt%)) blend films with different thickness (from 80 nm to 340 nm) were characterized. The dissociation efficiency of photo generated e-h pairs determined from photo current-effective voltage characteristics. The dissociation efficiency is strongly involved with fill factor and short circuit current of solar cells. The maximum photo current was increased and dissociation efficiency shows decreasing tendency as increasing thickness of active layer. Therefore, short circuit current density was slightly increased and saturated as thickness of active layer increased but the fill factor decreased sharply over the thickness with 120 nm. As a result, the maximum power conversion efficiency of 3.1 % exhibited at thickness of 120 nm under AM 1.5 100 mW/cm² illumination.