Effect Of Halogen Substitution On The Photoelectric Properties Of 2D-RP All-inorganic Double Perovskite Cs₄AgBiX₈

Recently,organic-inorganic hybrid perovskite solar cell materials have developed rapidly,especially lead halogen perovskite,which has the advantages such as suitable band gap,high light absorption efficiency and long luminous life.However,it is undeniable that the lead containing compounds face the challenge of the toxicity of lead and cannot be commercialized on a large scale.The emergence of double perovskites successfully avoids this problem,but the organic-inorganic composition makes it still unstable.All-inorganic double perovskite is a good choice because its all-inorganic composition improves its stability and its leadfree content makes it more widely used.Due to the influence of dimension,two-dimensional（2D）all-inorganic double perovskite may have better performance than its corresponding three-dimensional（3D）structure,and is more suitable for environment-friendly and efficient photoelectric materials.However,there are still few studies on the performance regulation of 2D all-inorganic double perovskite.For example,the effect of halogen substitution on the photoelectric performance of 2D all-inorganic double perovskite is still unclear.Therefore,it is necessary to select an appropriate 2D all-inorganic structure and study the effect of halogen regulation on its photoelectric properties.Based on this,in this thesis,Cl atoms in 2D all-inorganic double perovskite Cs₄AgBiCl₈with Ruddlesden-Popper（RP）structure were gradually replaced with Br and I to study the effect of halogen substitution on the photoelectric properties of2D-RP all-inorganic double perovskite.The optical and electronic properties of2D-RP all-inorganic double perovskite Cs₄AgBiX₈（X=Cl,Br,I）were calculated by density functional theory（DFT）,including band structure,optical absorption spectrum,carrier mobilities and exciton-binding energy.The results are as follows:（1）Halogen substitution has significant influence on the photoelectric properties of materials:halogen substitution（Cl replaced by Br and I）reduces the band gap from2.706 eV to 2.221 eV and 1.715 eV.Halogen substitutions（Cl replaced by Br and I）contribute to improved light absorption,increased carrier mobilities,and reduced exciton-binding energies（from 1529.90 meV to 1268.70 meV and 941.71meV）.（2）Considering the influence of exciton effect in low dimensional materials,the GW-BSE method was used to calculate the light absorption,and it was proved that the exciton effect was obvious in 2D-RP inorganic structures.（3）The luminescence properties of Cs₄AgBiX₈（X=Cl,Br,I）were calculated.The emission peaks of Cs₄AgBiCl₈,Cs₄AgBiBr₈and Cs₄AgBiI₈were at 375 nm,390nm and 480 nm,emitted ultraviolet,violet and blue light,respectively.All the three materials have good monochromatic luminescence properties.In addition,the excellent performance of Cs₄AgBiI₈makes it a more promising luminescent material among the three.In conclusion,2D-RP all-inorganic double perovskite Cs₄AgBiX₈（X=Cl,Br,I）is a material with potential excellent luminescence performance.Our study will expand the theoretical exploration of 2D-RP all-inorganic double perovskite material in the field of luminescence or photovoltaic.