  Phase segregation is a critical phenomenon that influences the stability and
performance of mixed halide perovskite based opto-electronic devices. In
addition to the underlying physical mechanisms, the spatial pattern and
randomness of phase segregation significantly influence performance
degradation-a topic which, along with the multitude of parameter combinations,
has remained too complex to address so far. Given this, with MAPbI1.5Br1.5 as a
model system, here we address the influence of critical factors like the
spatial randomness of phase segregation, influence of ion migration, and the
effect of increased non radiative recombination at material interfaces.
Interestingly, our analytical model and detailed statistical simulations
indicate a unique trend-while the device performance degrades with initial
phase segregation, curiously, it recovers significantly during the later
stages. Indeed, our quantitative and predictive estimates are broadly
applicable to systems which undergo phase segregation and have interesting
implications to perovskite based optoelectronic devices-from stability concerns
to engineering approaches that attempt to arrest phase segregation.
