Structural phase transitions of bulk tin-based halide perovskites under pressure and excited-state properties of tin-based halide perovskites quantum dots under ultrafast laser pulses: a novel phase ppPv-Pnma(VI)

Abstract

The structural phase transitions of tin-based halide perovskites CsSnX₃ (X = Cl, Br, I) under pressures of 0–120 GPa have been investigated by employing first-principles calculations combined with the CALYPSO method. Our calculated results indicate that CsSnCl₃ undergoes three structural phase transitions, P4/mbm to ppPv-Pnma(VI) at 0.6 GPa, ppPv-Pnma(VI) to P2₁/c(IV) at 15 GPa, and P2₁/c(IV) to Imm2 at 34 GPa. Four structural phase transitions from Pnma to ppPv-Pnma(VI) at 0.9 GPa, ppPv-Pnma(VI) to P2₁/c(V) at 6.7 GPa, P2₁/c(V) to Imm2 at 43 GPa, and Imm2 to Cm at 100 GPa are observed in CsSnBr₃. Similarly, CsSnI₃ also undergoes four structural phase transitions, ppPv-Pnma to ppPv-Pnma(VI) at 3.4 GPa, ppPv-Pnma(VI) to ppPv-Pnma at 5.4 GPa, ppPv-Pnma to P2₁/c(VI) at 18 GPa, and P2₁/c(VI) to Cm at 85 GPa. Our study successfully predicted a novel phase—ppPv-Pnma(VI). More importantly, the ppPv-Pnma(VI) QDs exhibit a larger highest electron level (HEL) compared to other CsSnX₃ (X = Cl, Br, I) QDs, reflecting their pronounced optical response and potential for optoelectronic applications. Subsequently, we further investigate the effects of different laser wavelengths and functional groups on the optical properties of ppPv-Pnma(VI) QDs. In particular, the addition of OH⁻ functional groups significantly enhances the HEL of the three ppPv-Pnma(VI) QDs, providing a strategy to improve the optical properties of QDs by incorporating appropriate functional groups. Our research indicates that the size adjustment and the addition of suitable functional groups can improve the optical response of quantum dots, which provides some theoretical support for exploring other perovskite QDs with excellent photoelectric properties.