The isoindigo-bithiophene-based polymer (PII-2T) was synthesized as previously reported . The molecular weight (Mn = 19,883, Mw = 61,700, PDI = 3.1) was characterized using high temperature gel permeation chromatography at 150 °C in trichlorobenzene. The polymer solutions were prepared by dissolving the polymer in either chlorobenzene (anhydrous, 99.8%; Sigma-Aldrich Inc.) or a mixture of chlorobenzene and 10% v/v dimethylformamide (99.9%; Fisher Scientific). The solutions were then stirred at 80 °C for at least 12 hours prior to use. After heating, the solutions were removed to room temperature for 15 minutes prior to being used in all experiments.