Decreasing the aggregation of PCBM in P3HT/PCBM blend films by cooling the solution

The number of micro-sized PCBM aggregations in P3HT/PCBM blend films was reduced by cooling the solution at 0 °C. P3HT aggregated when the solution was kept at 0 °C for more than 4 h. These P3HT aggregations acted as crystal nucleus, resulting in a network of P3HT nanofibers formation in the spin coated films. Then, after thermal annealing the film at 140 °C for 1 h, the growth of PCBM micro-size aggregations was efficiently prevented by the dense network of P3HT nanofibers, which was formed before PCBM aggregated. As a result, the density of PCBM micro-size aggregations reduced from 6.2% to 1.0% compared to the room temperature solution.