Publication date: 22nd July 2026
Organic-inorganic metal halide perovskites have emerged as attractive materials for solar cells with power-conversion efficiencies of single-junction devices now reaching 28%. Combinatorial optical characterization approaches are vital for probing and analysing such their electronic properties and material stability. We here investigate mixed bromide-iodide perovskites which offer ideal bandgaps for tandem solar cells, but still suffer from light-induced halide segregation, which compromises their operational stability.
We reveal how crystalline film quality and halide segregation are critically affected by bromide fraction x in CH3NH3Pb(I1−xBrx)3 through macrostrain and ordered-phase formation [1]. We show that the overall amplitude of phase segregation follows a broadly symmetric distribution in compositional space, maximized near x = 0.5, but the potentially ordered compositions of CH3NH3PbIBr2 and CH3NH3PbI2Br diverge sharply, presenting particularly stable and unstable scenarios, respectively. Notably, halide segregation is shown to occur even below the widely quoted perceived threshold of x = 0.2. Such analysis highlights promising approaches to mitigate halide segregation, through engineering of macrostrained phases and local atomistic ordering.
In addition, we directly probe the impact of halide segregation on charge-carrier dynamics at the interface between a mixed-halide perovskite and charge transport layers by using a free-space synchronous multimodal spectroscopy approach, combining time-resolved microwave conductivity, time-resolved and steady-state photoluminescence [2]. We reveal that charge extraction from such iodide-rich domains is still surprisingly feasible, but competes with enhanced radiative recombination resulting from higher charge concentrations caused by funnelling into these minority phases.
Finally, we demonstrate that the while photoluminescence tracking is universally used to monitor such photoinstability, such data are not good measures of halide segregation [3]. We demonstrate that PL cannot accurately reflect the rate and extent of halide segregation because it is governed by charge funneling to iodide-rich minority domains, which is strongly influenced by additional factors, including luminescence efficiency, band energetics, and charge extraction.
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