Effect of dimensional expansion on carrier transport behaviors of the hexagonal Bi-based perovskite crystals

All-inorganic Cs₃Bi₂I₉ (CBI) halide perovskites are sought to be candidate for photoelectrical materials because of their low toxicity and satisfactory stability. Unfortunately, the discrete molecular [Bi₂I₉]³⁻ clusters limit the charge-transport behaviors. Herein, the defect halide perovskite based on trivalent Bi³⁺ is expanded to Cs₃Bi₂I₆Br₃ (CBIB). Centimeter-size CBIB single crystal (Φ 15 × 70 mm³) was grown by the vertical Bridgeman method. The powder X-ray diffraction analysis shows that CBIB has P3¯m1 structure with lattice parameters of a = b = 8.223 Å, c = 10.024 Å, α = β = 90° and γ = 120°. The density functional theory (DFT) calculations demonstrate that the charge density distribution was enhanced after the dimensional expansion. The enhancement of carrier transport ability of (00l) in-plane is characterized before and after dimensional improvement. The obtained CBIB₍₀₀₁₎ exhibited an electron mobility up to 40.03 cm² V⁻¹ s⁻¹ by time-of-flight (TOF) technique, higher than 26.46 cm² V⁻¹ s⁻¹ of CBI₍₀₀₁₎. Furthermore, the X-ray sensitivity increases from 707.81 μC Gy⁻¹ cm⁻² for CBI₍₀₀₁₎ to 3194.59 μC Gy⁻¹ cm⁻² for CBIB₍₀₀₁₎. This research will deepen our understanding of Bi-based perovskite materials and afford more promising strategies for lead-free perovskite optoelectronic devices modification.