Hybrid Organic Inorganic Perovskite Films. Glass substrates (1 mm  1 mm) were washed by sonicating in a soap and water bath, then with water, acetone, and isopropyl alcohol for 20 min each. The substrates were dried in an oven and 140 °C for at least 1 h. Hot precursor solutions were spin cast onto the substrates in non-ambient conditions (50 µL at 3000 rpm for 30 s). The films were then annealed at 110 °C for 5-25 min. Longer annealing times led to increase in the intensity of the peaks associated with PbI2 as observed by powder X-ray diffraction. For X-ray diffraction, the films were encapsulated in a mylar plastic sample holder. For optical studies, the films were encapsulated in between 2 pieces of transparent packing tape to protect the samples from exposure to ambient water. The films appeared to rapidly degrade upon exposure to ambient conditions (within a matter of minutes) as noted by a color change from black to light brown/clear.