Supporting Information Understanding the Phase Formation Kinetics of Nano- Crystalline Kesterite Deposited on Mesoscopic Scaffold via In-Situ Multi-Wavelength Raman Monitored Annealing

Experimental Section: Precursor preparation TiO2 mesoscopic film was prepared by doctor-blading of commercially available anatase paste (Dyesol, 18NR-T) on cleaned FTO glass, then slowly heated up to 450°C and kept for 30 min to form the porous mesoscopic film. After, there are three steps for the quaternary precursor to be insitu deposited and coated onto the mesoscopic TiO2 film: 1. 100 mL 0.02M SnCl2 and 0.16M Na2S aqueous solution were prepared separately in two containers. Then the as-prepared TiO2 film on FTO glass was immersed into aqueous cationic solution containing Sn2+ and aqueous anionic solution containing excess S2successively with one-minute interval time; the process was repeated for 10 times to form a SnSx coating on the walls of the TiO2 mesopores. 2. Similarly, ZnS was in-situ