Manipulating the Phase Distributions and Carrier Transfers in Hybrid Quasi‐Two‐Dimensional Perovskite Films

Quasi two‐dimensional perovskites are promising alternatives to conventional three‐dimensional perovskites because of their high stability and easy tunability. However, controlling the phase distribution according to device architecture remains a major challenge. Here, the manipulation of phase purity and vertical distribution proven by ultrafast transient absorption spectroscopy, and their effect on device characteristics are reported. By adding ethyl acetate as antisolvent, the growth direction of the perovskite film is flipped. CH 3 NH 3 Cl and dimethyl sulfoxide are used to slow the growth rate of the crystal, which gives better phase purity. The direction of carrier transfer is tuned accordingly. It is found that solar cell performance is more sensitive to phase purity relative to vertical distribution. These findings are of importance for the applications of quasi‐2D perovskites in different types of devices that require to change phase purity and vertical distribution.