Boosting Organic Solar Cell Performance via Light-Assisted Crystallization of P3HT:PCBM Blend

In this study, we explore the effect of halogen-light-assisted (LA) annealing on the crystallization of poly-(3-hexylthiophene) (P3HT) films and the morphology of P3HT:[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) blends, along with their impact on organic solar cell performance. Samples were annealed at various temperatures (100-120 °C) and durations (5-15 min) using both conventional hot plate (HP) and LA methods. Structural analysis showed that LA annealing significantly enhanced the crystallinity of P3HT films through improved in-plane molecular stacking. For the P3HT:PCBM blend layers, the best film quality and device performance were achieved with LA annealing at 100 °C for 15 min, resulting in a power conversion efficiency (PCE) of 3.10% compared to 2.22% for the HP-annealed counterpart. We further evaluated blends with different P3HT:PCBM ratios (1:0.6, 1:1, and 1:1.4) and found that P3HT-rich compositions, especially 1:0.6, benefited most from LA annealing, achieving better film morphology and higher efficiency. Charge transport and recombination behavior were studied through time-resolved photoluminescence, light-intensity-dependent J-V, and space charge limited current measurements. These analyses confirmed that LA annealing improves charge carrier mobility, reduces trap densities, and minimizes nonradiative recombination. Overall, our results demonstrate that LA annealing is an effective and scalable method to enhance both the material quality and photovoltaic performance in P3HT:PCBM-based solar cells.