Anisotropic optoelectronic properties of lead-free Cs₃Bi₂I₉ single-crystal photodetectors

Abstract

Abstract Lead-free halide perovskites have attracted widespread research interest due to their excellent optoelectronic properties and environmental friendliness. As one of the bismuth iodide compounds, Cs 3 Bi 2 I 9 perovskite has been extensively explored in the field of photovoltaic devices and radiation detectors due to their non-toxic lead-free components and excellent stability. In this work, we successfully grow large-sized Cs 3 Bi 2 I 9 single crystals (SC) with ( l 00) and (00 l ) crystal exposure facets by inverse temperature crystallization method. Under 525 nm light illumination with the intensity 15 mW cm −2 and 7 V bias, the ( l 00) Cs 3 Bi 2 I 9 SC shows 2 times higher photocurrent, 3.6 times higher responsivity, and 2.8 times higher detectivity than the (00 l ) Cs 3 Bi 2 I 9 SC, respectively. Superior response time in the scale of millisecond is obtained in both ( l 00) and (00 l ) Cs 3 Bi 2 I 9 SCs. Based on the first-principle calculation, the ( l 00) SC possesses a higher charge distribution density and a wider dispersion distribution than (00 l ) SC, suggesting that more electrons in the ( l 00) SC can be excited in a wider range. The tighter arrangement of Cs + and [BiI 6 ] − octahedra in the ( l 00) SC than (00 l ) SC leads to the anisotropic photoelectric performance in ( l 00) and (00 l ) Cs 3 Bi 2 I 9 SCs. Our results provide a strategy for the oriental growth of Cs 3 Bi 2 I 9 SCs and the design of anisotropic optoelectronic devices with excellent performance.