Elegant Molecular Iodine/Antisolvent Solution Engineering To Tune the Fermi Level of Perovskite CH3NH3PbI3

It is important to change the semiconducting behaviors of CH3NH3PbI3 (MAPbI3) perovskites to meet the needs for different applications, which requires efficient strategies for Fermi level tuning in MAPbI3. Previous studies reported that the Fermi level of MAPbI3 could be down-shifted when exposed to I2 vapor; such a down-shift of the Fermi level could be rationalized by the filling of iodine vacancies (VI’s), a donor-type defect in MAPbI3. However, it is difficult to control the amount of incorporated I2 into the MAPbI3 matrix; meanwhile, MAPbI3 degradation may also occur following I2 vapor exposure. Herein, we propose a controllable and facile method for iodine manipulation and Fermi level tuning of MAPbI3, in which molecular iodine dissolved in antisolvent is applied as the iodine source. After iodine manipulation, the best-performing MAPbI3 solar cell exhibits a power conversion efficiency of 17.7%, in contrast to 15.8% on the pristine MAPbI3. Steady-state and time-resolved photoluminescence measurements indicate that iodine-modified MAPbI3 possesses reduced defect density and enhanced charge-carrier lifetimes. Photoelectron spectroscopy analyses reveal a 120 meV down-shift of the Fermi level in iodine-modified MAPbI3, as compared to the control MAPbI3.