Analog Memristor of Lead‐Free Cs₄CuSb₂Cl₁₂ Layered Double Perovskite Nanocrystals as Solid‐State Electronic Synapse for Neuromorphic Computing

Abstract

devices has surged from 3.8% to 25.5%. [2] Furthermore, perovskites also exhibit fascinating properties, such as easy solution processing, bandgap tunability, narrow band absorption as well as emission, high quantum yield, long carrier diffusion length as well as lifetime, excellent carrier transport, and so on. [3] Despite these exciting features, the commercialization of lead-based perovskites encounters enormous challenges due to their poor stability in ambient condition and lead toxicity to the environment. Therefore, the search for nontoxic alternatives of lead (Pb) has recently become one of the most critical research directions in perovskites.The advancement to develop lead-free or lead-less perovskite materials is still far from satisfactory since the replacement of Pb often worsens the remarkable optoelectronic properties. For example, isovalent substitution of Pb 2+ by atoms like Sn 2+ and Ge 2+ negatively impacts the photovoltaic properties of the material due to rapid conversion to higher oxidation state to Sn 4+ and Ge 4+ , respectively. [4] Alternatively, heterovalent substitution (M(III) = Sb 3+ , Bi 3+ , Au 3+ , In 3+ , etc.) was also implemented to obtain Cs 3 M(III) 2 X 9 (X = Br, Cl, or I) 2D layered perovskite derivatives. [5] However, these materials generally depict poor properties, including low carrier mobility, indirect bandgap, and large optical gap for direct bandgap since the layers of corner connected M(III)-centered octahedral are separated by layers of cationic vacancies. [6] To overcome these complications, Vargas et al. first introduced 〈111〉-oriented vacancy-ordered cesium copper antimony chloride [Cs 4 Cu(II)Sb(III) 2 Cl 12 or CCAC] layered double perovskite structure in 2017, which shows a direct bandgap of 1.0 eV. [7] Interestingly, this material does not decompose even in the presence of high humidity and upon exposure to light unlike lead halide perovskite. Further, Singhal et al. reported an easy mechanochemical growth of CCAC with long-range magnetic ordering due to the presence of an unpaired electron through Cu II -d 9 electrons. [8] Bulk CCAC perovskite has low carrier mobility due to high electron effective mass, thus hindering further device application. [9] Brain-inspired artificial neural networks and neuromorphic computing are taking space to a new height based on solid-state memristor devices. Despite considerable progress already made, the use of lead-free double perovskite materials with direct bandgap can be recognized as a significant paradigm shift in this field. Here, growth, thin film deposition, and analog electroforming-free resistive switching property along with promising artificial synaptic and neural activities of lead-free layered cesium copper antimony chloride (Cs 4 CuSb 2 Cl 12 or CCAC) double perovskite nanocrystals are reported. Optical and structural characterizations of CCAC microcrystals (MCs) and nanocrystals (NCs) confirm the growth, the existence of direct bandgap, and <111> oriented monoclinic crystal phase of space group C2/m. Inte...

Contrasting analog and digital resistive switching memory characteristics in solution-processed copper(i) thiocyanate and its polymer electrolyte-based memristive devices

“…These I – V characteristics relate to the synaptic functions, such as potentiation and depression of the synaptic weight. 9,40,41 Hence, this is suggestive that the analog RS memory prepared with CuSCN has the propensity to show synaptic behavior and can be employed to implement neuromorphic computing. It is also observed in Fig.…”

All-green Cs4CuSb2Cl12 perovskite films deposited in situ by AACVD and their doping with F− ions for photodetectors and memdiodes

“…Table S2 (ESI †) compiles optical bandgap calculations for various CCSC crystal presentations from literature sources. 6,8,[13][14][15][19][20][21][22][23][24] In the case of microcrystalline CCSC, optical bandgap estimates range from 1 to 1.4 eV, while for CCSC nanocrystals, a widening bandgap is observed, varying from 1.56 to 2.2 eV. The optical bandgap of this perovskite structure is This journal is © The Royal Society of Chemistry 2023 attributed to nanoscale confinement and surface atom rearrangement influenced by crystal size, thus, the E g value found for the CCSC film indicates a nanocrystalline structure.…”

“…20 Interestingly, superior performance has been observed in CCAC NC thin film optoelectronic devices, likely because of the less defective growth of thin films from nanocrystals. 8 However, the proper charge transport among grains will be dependent on how densely the nanocrystals are packed, and the use of bulky organic ligands in their synthesis can further limit nanocrystal connectivity (Fig. 6c).…”

“…Cs 4 CuSb 2 Cl 12 is the first member of the VOLDPs family discovered by B. Vargas et al 6 Its small bandgap (o2 eV) that efficiently absorbs the entire visible spectrum, makes it a great candidate for photovoltaics. And even though one of its major appeals lies in the simplicity of synthesis as mono, micro, and nanocrystals, the deposition of thin films has only been achieved by the assembly of presynthesized nanocrystals and, [7][8][9] to the best of the author's knowledge, there are no reports of the deposition of Cs 4 CuSb 2 Cl 12 continuous films in situ. The low solubility of CsCl in most solvents, along with the fast crystallization and precipitation when the precursor chloride salts are mixed in a single solution, have hampered the application of wet techniques such as spin coating for film deposition.…”

Epitaxial La0.5Sr0.5MnO3‐δ Bipolar Memristive Devices with Tunable and Stable Multilevel States

“…In RS, the reversible change of resistance in a device between a high resistance state (HRS) and a low resistance state (LRS) is exploited to store the information, as for the regular binary storage. RS has been previously reported in a large sort of materials, [2] where depending on the materials' properties and the electrodes, the change of resistance can have different phenomenological origins. [3][4][5][6][7] In the case of valence change memories (VCMs), the change of resistance is related to the variable oxygen content and the concomitant change of valence in the cationic sublattice, which ultimately modifies the resistivity of the material.…”