Controlled Synthesis of Lead-Free and Stable Perovskite Derivative Cs₂SnI₆ Nanocrystals via a Facile Hot-Injection Process

Abstract

Colloidal nanocrystals of lead halide perovskites have recently received great attention due to their remarkable performance in optoelectronic applications (e.g., light-emitting devices, flexible electronics, and photodetectors). However, the use of lead remains of great concern due to its toxicity and bioaccumulation in the ecosystem; herein we report a strategy to address this issue by using tetravalent tin (Sn 4+ ) instead of divalent lead (Pb 2+ ) to synthesize stable Cs 2 SnI 6 perovskite nanocrystals. The shapes of assynthesized Cs 2 SnI 6 nanocrystals are tuned from spherical quantum dots, nanorods, nanowires, and nanobelts to nanoplatelets via a facile hot-injection process using inexpensive and nontoxic commercial precursors. Spherical aberration corrected scanning transmission electron microscopy (Cs-corrected STEM) and simulation studies revealed a well-defined face-centered-cubic (fcc) perovskite derivative structure of Cs 2 SnI 6 nanocrystals. The solution-processed Cs 2 SnI 6 nanocrystal-based field effect transistors (FETs) displayed a p-type semiconductor behavior with high hole mobility (>20 cm 2 /(V s)) and high I-ON/I-OFF ratio (>10 4 ) under ambient conditions. We envision that this work will pave the way to produce new families of high-performance, stable, low-cost and nontoxic nanocrystals for optoelectronic applications.

Progress of Lead‐Free Halide Double Perovskites

“…[111] Cs 2 AgBiBr 6 NCs were achieved by injecting Csoleate at 200 °C into a high boiling organic solvent containing BiBr 3 and AgNO 3 . [112] It involved a reaction at 220 °C and in ambient between Cs-oleate and tin(IV) iodide in the presence of oleylamine and oleic acid using octadecane as the solvent. The quality of Cs 2 AgBiBr 6 NCs could be improved by a deliberate control of the HBr and oleic acid/oleylamine (OA/ OLA) additives and the reaction temperature.…”

“…Their crystal structure is depicted by Maughan et al, as shown in Figure 9a,b. Although there are some conflicting reports [88,112,124,169] on the room temperature carrier mobility of Cs 2 SnI 6 , the origin of conductivity in this compound has been hypothesized to stem from (a) the possession of dispersive conduction band states and (b) the presence of iodine vacancies. Cs 2 SnI 6 compound exhibits intrinsic n-type electrical conductivity and other fascinating features such as direct bandgap, air and moisture stability, and strong visible light absorption.…”

“…[112] Tan et al fabricated a highly efficient light-emitting diode (LED) chip by choosing Cs 2 SnCl 6 as a host and Bi 3+ as the luminescent dopant. Despite the limited available application, a few members of this class of compounds have been applied as suitable functional layers in various optoelectronic devices.…”

Recent advances and prospects toward blue perovskite materials and light‐emitting diodes

“…The Sn‐based system is also a promising Pb‐free blue perovskite material. Unfortunately, the PLQYs of Sn‐based perovskite NCs (CsSnX 3 and Cs 2 SnX 6 ), are generally low due to the oxidation process from Sn (II) to Sn (IV) . Compared with Bi‐based perovskites, Sn‐based perovskites have a great deal of intrinsic defect sites.…”

Organic–inorganic metal halide hybrids beyond perovskites

“…LEDs (Figure 2(c)), optically pumped lasers (Figure 2(d)), etc [32][33][34]. To address the toxicity issue of Pb, 3D tin halide perovskites have been developed [35][36][37][38][39]. However, bivalent Sn 2+ could be easily oxidized to Sn 4+ , resulting in the instability of the material itself and morphological change into other species [40].…”