A Comparative Study on the Optimization of a Ternary P3HT:PCBM:Pentacene Active Layer in Bulk Heterojunction Organic Solar Cells

This work shows a comparative and processing optimization study of the recent ternary bulk heterojunction (BHJ) of P3HT: PCBM:pentacene (1:0.9:0.1 wt. ratio) against the well-known active layer of poly(3-hexylthiophene) (P3HT) blended to phenyl C61 butyric acid methyl ester (PCBM) (1:1 wt. ratio). Initially, monochlorobenzene (MCB) was compared and later replaced by dichlorobenzene (DCB) as active layer solvent. The following optimization step related to thermal annealing effects on solar cell power conversion efficiency (PCE) and fill-factor (FF). Ternary junction slow drying at room temperature without a postproduction thermal treatment proved to be the most suitable to improve BHJ morphology at nanoscale. Finally, ternary composite mass concentration ranged from 20 to 60 mg/ml in DCB to achieve an efficiency near 3% at 40 mg/ml. An observed improvement of at least 15% in photovoltaic efficiency and a practically constant open-circuit voltage (i.e., just 1.2% variation) compared to the already-established P3HT:PCBM blend corroborates the role of pentacene in the active layer to balance mobility from both charge carrier types.