Real time observation of photo-instability of ternary-halide mixed CH3NH3Pb(Br1-x-yClxIy)3 perovskite: Preferential diffusion of small halide ions

In this study, we attempted to improve the optical stability via the complicated design of the X site composition of CH3NH3Pb(Br1-x-yClxIy)(3), such as CH3NH3Pb(Br0.5I0.5)(3) and CH3NH3Pb(Br0.5Cl0.25I0.25)(3). It was observed that photo-stability improvement via the complicated design of the X site composition of CH3NH3Pb(Br1-x-yClxIy)(3) would not occur. I-rich phase which was remained phase after small halide ion (Br or/and Cl) extraction was unavoidably formed through the preferential extraction of small halide ions, and this can be explained by the spinodal decomposition mechanism. Comparing the excitation dynamics of MAPb(Br0.5I0.5)(3) and MAPb(Br0.5I0.25Cl0.25)(3), we could expect that the excitation dynamics would be relatively complicated in the presence of Cl. The reason for this is explained by the effect of mixed mobile ions, i.e., small ions are more easily diffused than large ions. (C) 2019 Elsevier B.V. All rights reserved.