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

All-inorganic Cs 3 Bi 2 I 9 (CBI) halide perovskites are sought to be candidate for photoelectrical materials because of their low toxicity and satisfactory stability. Unfortunately, the discrete molecular [Bi 2 I 9 ] 3− clusters limit the charge-transport behaviors. Herein, the defect halide perovskite based on trivalent Bi 3+ is expanded to Cs 3 Bi 2 I 6 Br 3 (CBIB). Centimeter-size CBIB single crystal ( Φ 15 × 70 mm 3 ) was grown by the vertical Bridgeman method. The powder X-ray diffraction analysis shows that CBIB has P 3 ¯ m 1 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 (00 l ) in-plane is characterized before and after dimensional improvement. The obtained CBIB (001) exhibited an electron mobility up to 40.03 cm 2 V −1 s −1 by time-of-flight (TOF) technique, higher than 26.46 cm 2 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.