Pressure-induced Structural Evolution And Optoelectric Properties Of Antimony-iodine-based Perovskite-like Materials

Metal halide perovskites?MHPs?has become a research hotspot in the field of photovoltaic optoelectronic materials due to its excellent photoelectric performance,low cost and high power conversion efficiency?PCE?,and has been widely used in solar cells,LEDs,lasers and photocatalysis.In a short time,the PCE has increased from the initial reported rate of 3.8 to above 23%.However,the large-scale use of these materials is limited by the effects of toxic heavy metals such as lead and long-term stability under environmental conditions.To avoid these problems,A₃M₂X₉ lead-free metal halide perovskite-like materials have become hot materials in recent research because of their unique low toxicity and better chemical stability?A is a monovalent metal or organic group,M is a trivalent metal,and X is a halide anion coordinated to the metal?.However,the wide band gap of such materials is difficult to meet the needs of practical applications.Therefore,using clean and effective high-pressure means to regulate it and exploring the relationship between its crystal structure and optoelectronic properties can provide solid theoretical support for this material's wide-scale application in the future.In this paper,two representative lead-free metal halide perovskites-like are selected as research objects.First,a high-pressure study was performed on the Cs₃Sb₂I₉crystal.The DAC device was used to study the crystal in combination with in-situ high-pressure UV-visible absorption spectrum,in-situ high-pressure synchrotron radiation X-ray diffraction spectrum,in-situ high-pressure Raman spectrum,in-situ high-pressure electrical experiment,and first-principles calculation simulation.At 20.0 GPa,Cs₃Sb₂I₉ with a wide band gap?2.34 eV?successfully reached the Shockley-Queisser limit?1.34 eV?,accompanied by a clear piezochromism from orange-yellow to opaque black.At the same time,Cs₃Sb₂I₉ has undergone a completely reversible amorphization in the entire pressure range up to 20 GPa.These optical changes can be attributed to the decrease in bond length of the Sb-I bond and the Sb-I bond at the bridge end,and the decrease of the bond angle between the I-Sb-I bond angle and the Sb-I-Sb bond angle as the pressure increases,which results in enhanced atomic orbital coupling.In addition,under the pressure of 44.3 GPa,the Cs₃Sb₂I₉ insulating crystal,which originally had a very large resistance(1.5×10¹²?),finally exhibited the properties of metal conductors and realized metallization,thereby revealing the new electronic and transmission properties of this metal halide material.Subsequently,we obtained MA₃Sb₂I₉ crystals similar to the Cs₃Sb₂I₉ crystal structure by cation substitution.Considering that the difference in cation size will affect the high-pressure band-gap regulation of such materials to a certain extent,high-pressure studies on MA₃Sb₂I₉ crystals were performed.Through in-situ high-pressure UV-visible absorption spectrum analysis,we found that as the pressure increases,the band gap of MA₃Sb₂I₉ gradually decreases,and finally at 20 GPa,it decreases from the initial wide band gap of 2.43 eV to 1.63 eV.The band gap compression rate is as high as 32.5%.At the same time,there is a clear piezochromism from orange yellow-orange-orange red-dark red during the compression process.The wide band narrowing and piezochromism processes of the entire crystal are completely reversible.Combining in-situ high-pressure synchrotron X-ray diffraction and in-situ high-pressure Raman spectroscopy,the study found that these optical changes can be attributed to the variant and distortion of the crystal Sb-I octahedral network structure under high pressure.The experimental conclusions in this article clarify that the high-pressure technology has an excellent regulation effect on the crystal structure and optoelectronic properties of perovskite-like materials,and provides new ideas for designing semiconductor materials with excellent optoelectronic properties.