Annealing and thickness dependent enhanced-efficiency of P3HT:PCBM organic solar cells

The influence of thermal annealing on the performance of a poly(3-hexylthiophene-2,5-diyl) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) organic solar cells with an aluminum cathode was systematically investigated for varying active-layer thicknesses. Devices were fabricated using single (10 mg·ml −1 ) and double (20 mg·ml −1 ) P3HT concentrations, and the effect of spin-coating speed on film morphology and device performance was evaluated. Pre- and post-annealing treatments were applied at 100, 120, 140, and 160 °C for 30 minutes, with a two-step post-annealing process at 160 °C for 30 minutes followed by 180 °C for 10 minutes. Optical absorption spectroscopy, atomic force microscopy, and current–voltage measurements were employed to assess the effects on light harvesting and photovoltaic parameters. The highest efficiency of 2.1% was achieved for an 80-nm-thick film prepared at 1000 rpm with double-concentration P3HT after the two-step post-annealing. This treatment increased the optical absorption of the active layer by 12% and enhanced device performance, resulting in a 5.8% power conversion efficiency improvement. The results highlight the critical role of annealing temperature, timing, film thickness, and spin-coating speed in optimizing P3HT:PCBM OSC performance.