In the case of FAMAPbI3, (sample in figure ) the mixture of FAI, MAI, and PbI2 at the ratio of 1:1:2 with the same concentration was dissolved in 0.4 ml of DMSO and 0.6 ml of DMF. Two solutions were stirred in a glove box for 12 hours. The substrate used was glass/ITO/ PEDOT:PSS.