[Chinese Journal of Science] Perovskite structure modulation affects photo-generated charge separation and transport properties

Source: China Science News

Recently, Academician Li Can and Researcher Li Rengui of the Dalian Institute of Chemical Physics of the Chinese Academy of Sciences have made new progress in the study of the structural modulation and photoelectric properties of perovskite materials, and discovered that the internal octahedral distortion of the all-inorganic lead-free halide perovskite structure Elimination significantly reduces the localization of electron-hole pairs, greatly enhances the separation and transmission of photo-generated charges, and exhibits excellent photoelectric properties. Relevant research results were published on "Advanced Materials".

Metal halide perovskites have received extensive attention from researchers due to their excellent optical and electrical properties (such as high light absorption coefficient, low exciton binding energy, high carrier mobility and long diffusion length, etc.), and have been used in Various optoelectronic fields.

The researchers selected Cs3Bi2Br9, a typical inorganic halide perovskite semiconductor as the research object, and combined theoretical calculations and experiments, and found that the distortion of the BiBr6 octahedral structure in Cs3Bi2Br9 makes the excited electron-hole pairs strongly localized in bismuth ( Bi) center, which produces a great exciton binding energy, which hinders the separation and transmission of photo-generated charges. Furthermore, by introducing silver (Ag) atoms to replace part of bismuth (Bi) atoms into its structure, the double perovskite Cs2AgBiBr6 is formed. Silver (Ag) occupies the original vacancies, eliminating the structural distortion of the octahedron, and greatly reducing the electrons— The strong localization of hole pairs makes the electron distribution in the conduction band and valence band more dispersed. Therefore, compared with Cs3Bi2Br9, Cs2AgBiBr6 has lower exciton binding energy, lower effective carrier mass, higher carrier mobility, and longer effective life, which greatly improves the separation and transport properties of photo-generated charges.

Li Rengui introduced: “Our team used the photocatalytic hydrogen production reaction under visible light as a probe reaction and found that the modulation of the perovskite microstructure increased the photocatalytic hydrogen production activity by more than two orders of magnitude, further verifying the structure adjustment of the perovskite. Change has an important impact on the separation and transport properties of photogenerated charges."

This work is of great significance for understanding the essential relationship between the microstructure of perovskite semiconductors and its optoelectronic properties, rationally designing and guiding the application of new perovskite material systems in the optoelectronic field.

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