Light-Induced Phase Segregation in Halide-Perovskite Absorbers

Abstract

In the few short years since the inception of single-junction perovskite solar cells, their efficiencies have skyrocketed. Perovskite absorbers have at least as much to offer tandem solar cells as they do for single-junction cells due in large part to their tunable band gaps. However, modifying the perovskite band structure via halide substitution, the method that has been most effective at tuning band gaps, leads to instabilities in the material for some compositions. Here, we discuss the thermodynamic origin and consequences of light-induced phase segregation observed in mixed-halide perovskites. We propose that, as the phase segregation is rooted in halide migration and possibly affected by lattice strain, modifying the perovskite composition and lattice structure, increasing compositional uniformity, and reducing defect concentrations could significantly improve stability.

Combination of Hybrid CVD and Cation Exchange for Upscaling Cs‐Substituted Mixed Cation Perovskite Solar Cells with High Efficiency and Stability

“…Phase segregation of mixed perovskites has been reported to be detrimental for both device performance and stability. [34,36,39,66] The full width half maximum (FWHM) values of the PL peaks were extracted to show the phase purity on various mixed perovskite samples ( Figure S6, Supporting Information).…”

“…Different Cs + ratios between perovskite surface and bulk could significantly affect the device PCE and stability. [37,39,66] High-resolution X-ray photoemission spectroscopy (HRXPS) measurements were performed on the A, B, C, D, and E perovskite films to analyze the element ratios at surface, and then compare with the bulk. Except for Sample A, all other samples show two symmetric peaks at 739.0 and 725.0 eV, which are assigned to the Cs 3d 3/2 and 3d 5/2 peaks, respectively (Figure 5a).…”

The Emergence of the Mixed Perovskites and Their Applications as Solar Cells

“…McGehee et al speculates this ion migration strongly linked with the J−V hysteresis. [172] Recent research has demonstrated that halide migration is promoted by halogen vacancies [174] and migrated faster at the grain boundary compared to that of the grain interior. [175] This implies that reducing grain boundary density maybe an effective way to alleviate phase separation.…”

Characterization of optically active perovskite electrodes

“…[61,63,139] Several research groups have evaluated solar cell performance under short-term irradiation and they considered the photovoltaic performance to be stable. [140] Halide ion migration in PSCs plays an important role in determining the overall photovoltaic performance. [141][142][143] Light soaking, for example, leads to migration of ions and vacancies toward the oxide interface influencing the observed photovoltage.…”

“…[144] Another property of the mixed halide lead perovskite is its ability to undergo phase segregation under continuous illumination. [80,140,[145][146][147][148] For example, when MAPbX3 (X = Br, I, 1:1 ratio) is subjected to long-term (> 20 min) visiblelight irradiation, it undergoes phase segregation to yield iodide rich and bromide rich domains as described by Eq. 9.…”