Abstract
Mixed halide hybrid perovskites, CH3NH3Pb(I1−xBrx)3, represent good candidates for low-cost, high efficiency photovoltaic, and light-emitting devices. Their band gaps can be tuned from 1.6 to 2.3 eV, by changing the halide anion identity. Unfortunately, mixed halide perovskites undergo phase separation under illumination. This leads to iodide- and bromide-rich domains along with corresponding changes to the material’s optical/electrical response. Here, using combined spectroscopic measurements and theoretical modeling, we quantitatively rationalize all microscopic processes that occur during phase separation. Our model suggests that the driving force behind phase separation is the bandgap reduction of iodide-rich phases. It additionally explains observed non-linear intensity dependencies, as well as self-limited growth of iodide-rich domains. Most importantly, our model reveals that mixed halide perovskites can be stabilized against phase separation by deliberately engineering carrier diffusion lengths and injected carrier densities.
Highlights
Mixed halide hybrid perovskites, CH3NH3Pb(I1−xBrx)[3], represent good candidates for lowcost, high efficiency photovoltaic, and light-emitting devices
MAPb(I1−xBrx)[3] phase separation is key to engineering and controlling the stability of mixed halide perovskites for photovoltaic as well as other optoelectronic applications[17,18,19]
As an added control to verify that phase separation arises from suppressed charge diffusion lengths and not from the limited nanocrystal size in nanocrystal-based films, we show in Supplementary Fig. 8 that at high excitation intensities (Iexc = 500 W cm−2) phase separation in nanocrystal-based films can be turned on
Summary
CH3NH3Pb(I1−xBrx)[3], represent good candidates for lowcost, high efficiency photovoltaic, and light-emitting devices. Their band gaps can be tuned from 1.6 to 2.3 eV, by changing the halide anion identity. Mixed halide perovskites undergo phase separation under illumination This leads to iodide- and bromide-rich domains along with corresponding changes to the material’s optical/electrical response. Our model suggests that the driving force behind phase separation is the bandgap reduction of iodiderich phases It explains observed non-linear intensity dependencies, as well as self-limited growth of iodide-rich domains. MAPb(I1−xBrx)[3] exhibits unwanted instabilities under visible light irradiation, leading to I and Br segregation into separate iodide- and bromide-rich domains. MAPb(I1−xBrx)[3] phase separation is key to engineering and controlling the stability of mixed halide perovskites for photovoltaic as well as other optoelectronic applications[17,18,19]
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