Lead‐Free Perovskite Derivative Cs₂SnCl_6−xBr_x Single Crystals for Narrowband Photodetectors

Abstract

Recently, lead-based perovskite materials with the formula APbX 3 (A = Cs, methylammonium; X = Cl, Br, I) have received broad attention for their excellent optical and electronic properties in the fields of photovoltaic solar cells, [1] light-emitting diodes (LEDs), [2] sensitive photodetectors, [3] etc. However, the presence of toxic lead and unsatisfactory stability against heat and humidity restrict their further application. [4] An effective method to solve these issues is to replace divalent Pb with tetravalent Sn, forming a molecular salt structure with the formula A 2 SnX 6 (X = Cl, Br, I), which is a 50% Sn defect perovskite derivative featuring isolated [SnX 6 ] 2− octahedra. [5] This substitution can not only result in long-term stability in air but also maintain the high-symmetry cubic structure with a different halogen X Lead-free and stable Sn halide perovskites demonstrate tremendous potential in the field of optoelectronic devices. Here, the structure and optical properties of the "defect" perovskites Cs 2 SnCl 6−x Br x are reported, as well as their use as photodetector materials. Millimeter-sized Cs 2 SnCl 6−x Br x single crystals are grown by the hydrothermal method, with the body color continuously changing from transparent to yellow and finally to dark red. Narrowband single-crystal photodetectors using Cs 2 SnCl 6−x Br x crystals are presented, which show a high detectivity of ≈2.71 × 10 10 Jones, with narrowband photodetection (full-width at half-maximum ≈45 nm) and high ion diffusion barriers. Moreover, the response spectra are continuously tuned from near violet to orange depending on the variation of the bandgap of the single crystals by changing the halide compositions. The strong surface charge recombination of the excess carriers near the crystal surfaces produced by short wavelength light elucidates the narrowband photodetection behavior. This work provides a new paradigm in the design of lead-free, stable, and high-performance perovskite derivatives for optoelectronics applications.

Lead-Free Perovskites for Lighting and Lasing Applications: A Minireview

“…To replace Pb (II) in halide perovskites, several low-toxic cations from the same group of periodical table and those closest to it were proposed, including Sn(II) [28,29,30,31,32], In (III) [33,34], Bi(III) [35,36,37,38,39,40], Sb(III) [41], and others. At the same time, the double perovskite structure gained distribution in lead-free perovskites due to the wide range of cations from III group mixed with Ag(I) [42,43,44,45,46,47,48,49].…”

Lead‐Free Double Perovskites for Perovskite Solar Cells

“…Zhou et al fabricated narrowband photodetectors based on a photoconductive structure which used millimeter‐sized Cs 2 SnCl 6− x Br x single crystals by the hydrothermal method . The response spectra of photodetectors can be continuously tuned from near violet to orange by changing the halide composition as well as the bandgap of synthesized single crystals.…”

Recent Progress on Advanced Optical Structures for Emerging Photovoltaics and Photodetectors

“…Rao et al, [ 210 ] Saidaminov et al, [ 211 ] and Zhou et al [ 212 ] used thick perovskite layers to fabricate self‐filtered PePDs, with Rao et al using MAPbBr 3 , Saidaminov et al using MAPbX 3 (X = Cl, Br, I), and Zhou et al using Cs 2 SnCl 6– x Br x as their active layers. The PePD prepared by Rao et al exhibited narrowband detection centered near 570 nm (FWHM = 35 nm) with a broad linear response from 10 −4 to 10 −2 mW cm −2 , a high wavelength selectivity of 61.3 dB, and a 3‐dB cutoff frequency (f3dB) of 110 kHz under a low bias of –1 V. The photoresponse of the perovskite photodetectors developed by Zhou et al could be tuned from 400 to 600 nm, with an FWHM of 45 nm and a high detectivity of 2.71 × 10 10 Jones.…”