Why most of the people used FTO instead of ITO for perovskite solar cell fabrication? I know the band gap of ITO and FTO is 4.9eV and 4.4eV respectively, but is this will make any different?
In my experience, FTO is typically rougher than ITO, giving ITO an advantage in smooth film formation. However ITO sheet resistance will increase with heating, causing a higher series resistance in the final device. Some think this is a necessary trade off for higher efficiency devices.
Adding to George FTO has higher transparency than ITO and it is less expensive,
For more detailed comparison between the two materials please follow the link: http://onlinelibrary.wiley.com/doi/10.1002/(SICI)1521-4095(199808)10:11%3C859::AID-ADMA859%3E3.0.CO;2-1/abstract.
I would add that many people prepare perovskite onto TiO2 deposited over FTO. TiO2 often needs to be processed at high temperatures (like 450°C) to reach high condictivity. That's why you need to use the temperature-stable FTO, to be covered with TiO2 and then with perovskite, instead of ITO.