Substrate treatment: All samples, unless otherwise specified, are fabricated on 1 cm x 1 cm soda-lime glass of thickness 1.1 mm. All substrates were washed by sonicating for 10 minutes in a 1% Hellmanex detergent solution in deionized water, followed by two 5minutes sonications in deionized water, followed by two 5-minute sonications in acetone, and two 5-minute sonications in isopropanol. The substrates were then dried under pressurized air to remove solvent and dust particles. Within 15 minutes before spin coating, the glass substrates were treated with UV ozone plasma for at least 15 minutes.