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1. Sr(Ag _1−x Li _x ) ₂ Se ₂ and [Sr ₃ Se ₂ ][(Ag _1−x Li _x ) ₂ Se ₂ ] Tunable Direct Band Gap Semiconductors

   https://doi.org/10.1002/anie.202301191  

   Zhou, Xiuquan; Wilfong, Brandon; Chen, Xinglong; Laing, Craig; Pandey, Indra R.; Chen, Ying‐Pin; Chen, Yu‐Sheng; Chung, Duck‐Young; Kanatzidis, Mercouri G. (February 2023, Angewandte Chemie International Edition)

   Abstract Synthesizing solids in molten fluxes enables the rapid diffusion of soluble species at temperatures lower than in solid‐state reactions, leading to crystal formation of kinetically stable compounds. In this study, we demonstrate the effectiveness of mixed hydroxide and halide fluxes in synthesizing complex Sr/Ag/Se in mixed LiOH/LiCl. We have accessed a series of two‐dimensional Sr(Ag_1−xLi_x)₂Se₂layered phases. With increased LiOH/LiCl ratio or reaction temperature, Li partially substituted Ag to form solid solutions of Sr(Ag_1−xLi_x)₂Se₂withxup to 0.45. In addition, a new type of intergrowth compound [Sr₃Se₂][(Ag_1−xLi_x)₂Se₂] was synthesized upon further reaction of Sr(Ag_1−xLi_x)₂Se₂with SrSe. Both Sr(Ag_1−xLi_x)₂Se₂and [Sr₃Se₂][(Ag_1−xLi_x)₂Se₂] exhibit a direct band gap, which increases with increasing Li substitution (x). Therefore, the band gap of Sr(Ag_1−xLi_x)₂Se₂can be precisely tuned via fine‐tuningxthat is controlled by only the flux ratio and temperature. 

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2. Enhanced Efficiency and Stability in Sb ₂ S ₃ Seed Layer Buffered Sb ₂ Se ₃ Solar Cells

   https://doi.org/10.1002/admi.202200547  

   Amin, Al; Li, Dian; Duan, Xiaomeng; Vijayaraghavan, S_N; Menon, Harigovind_G; Wall, Jacob; Weaver, Mark; Cheng, Mark_Ming‐Cheng; Zheng, Yufeng; Li, Lin; et al (May 2022, Advanced Materials Interfaces)

   Abstract Antimony selenide (Sb₂Se₃) has excellent directional optical and electronic behaviors due to its quasi‐1D nanoribbons structure. The photovoltaic performance of Sb₂Se₃solar cells largely depends on the orientation of the nanoribbons. It is desired to grow these Sb₂Se₃ribbons normal to the substrate to enhance photoexcited carrier transport. Therefore, it is necessary to develop a strategy for the vertical growth of Sb₂Se₃nanoribbons to achieve high‐efficiency solar cells. Since antimony sulfide (Sb₂S₃) and Sb₂Se₃are from the same space group (Pbnm) and have the same crystal structure, herein an ultrathin layer (≈20 nm) of Sb₂S₃has been used to assist the vertical growth of Sb₂Se₃nanoribbons to improve the overall efficiency of Sb₂Se₃solar cell. The Sb₂S₃thin layer deposited by the hydrothermal process helps the Sb₂Se₃ribbons grow normal to the substrate and increases the efficiency from 5.65% to 7.44% through the improvement of all solar cell parameters. This work is expected to open a new direction to tailor the Sb₂Se₃grain growth and further develop the Sb₂Se₃solar cell in the future. 

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3. Solution‐Processed Sb ₂ (S,Se) ₃ Seed‐Assisted Sb ₂ Se ₃ Thin Film Growth for High Efficiency Solar Cell

   https://doi.org/10.1002/solr.202400151  

   Amin, Al; Duan, Xiaomeng; Zhao, Kaiji; Khawaja, Kausar; Xiang, Wenjun; Qian, Xiaofeng; Yan, Feng (May 2024, Solar RRL)

   Antimony selenide (Sb₂Se₃) emerges as a promising sunlight absorber in thin film photovoltaic applications due to its excellent light absorption properties and carrier transport behavior, attributed to the quasi‐one‐dimensional Sb₄Se₆‐nanoribbon crystal structure. Overcoming the challenge of aligning Sb₂Se₃‐nanoribbons normal to substrates for efficient photogenerated carrier extraction, a solution‐processed nanocrystalline Sb₂(S,Se)₃‐seeds are employed on the CdS buffer layer. These seeds facilitate superstrated Sb₂Se₃thin film solar cell growth through a close‐space sublimation approach. The Sb₂(S,Se)₃‐seeds guided the Sb₂Se₃absorber growth along a [002]‐preferred crystal orientation, ensuring a smoother interface with the CdS window layer. Remarkably, Sb₂(S,Se)₃‐seeds improve carrier transport, reduce series resistance, and increase charge recombination resistance, resulting in an enhanced power conversion efficiency of 7.52%. This cost‐effective solution‐processed seeds planting approach holds promise for advancing chalcogenide‐based thin film solar cells in large‐scale manufacturing. 

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4. Charge Transfer Modulation in Vanadium‐Doped WS ₂ /Bi ₂ O ₂ Se Heterostructures

   https://doi.org/10.1002/smll.202302289  

   Chitara, Basant; Dimitrov, Edgar; Liu, Mingzu; Seling, Tank R.; Kolli, Bhargava S. C.; Zhou, Da; Yu, Zhuohang; Shringi, Amit K.; Terrones, Mauricio; Yan, Fei (June 2023, Small)

   Abstract The field of photovoltaics is revolutionized in recent years by the development of two–dimensional (2D) type‐II heterostructures. These heterostructures are made up of two different materials with different electronic properties, which allows for the capture of a broader spectrum of solar energy than traditional photovoltaic devices. In this study, the potential of vanadium (V)‐doped WS₂is investigated, hereafter labeled V‐WS₂, in combination with air‐stable Bi₂O₂Se for use in high‐performance photovoltaic devices. Various techniques are used to confirm the charge transfer of these heterostructures, including photoluminescence (PL) and Raman spectroscopy, along with Kelvin probe force microscopy (KPFM). The results show that the PL is quenched by 40%, 95%, and 97% for WS₂/Bi₂O₂Se, 0.4 at.% V‐WS₂/Bi₂O₂Se, and 2 at.% V‐WS₂/Bi₂O₂Se, respectively, indicating a superior charge transfer in V‐WS₂/Bi₂O₂Se compared to pristine WS₂/Bi₂O₂Se. The exciton binding energies for WS₂/Bi₂O₂Se, 0.4 at.% V‐WS₂/Bi₂O₂Se and 2 at.% V‐WS₂/Bi₂O₂Se heterostructures are estimated to be ≈130, 100, and 80 meV, respectively, which is much lower than that for monolayer WS₂. These findings confirm that by incorporating V‐doped WS₂, charge transfer in WS₂/Bi₂O₂Se heterostructures can be tuned, providing a novel light‐harvesting technique for the development of the next generation of photovoltaic devices based on V‐doped transition metal dichalcogenides (TMDCs)/Bi₂O₂Se. 

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5. In ₂ Se ₃ Synthesized by the FWF Method for Neuromorphic Computing

   https://doi.org/10.1002/aelm.202400603  

   Shin, Jaeho; Jang, Jingon; Choi, Chi_Hun; Kim, Jaegyu; Eddy, Lucas; Scotland, Phelecia; Martin, Lane_W; Han, Yimo; Tour, James_M (November 2024, Advanced Electronic Materials)

   Abstract The development of next‐generation in‐memory and neuromorphic computing can be realized with memory transistors based on 2D ferroelectric semiconductors. Among these, In₂Se₃is the interesting since it possesses ferroelectricity in 2D quintuple layers. Synthesis of large amounts of In₂Se₃crystals with the desired phase, however, has not been previously achieved. Here, the gram‐scale synthesis of α‐In₂Se₃crystals using a flash‐within‐flash Joule heating method is demonstrated. This approach allows the synthesis of single‐phase α‐In₂Se₃crystals regardless of the conductance of precursors in the inner tube and enables the synthesis of gram‐scale quantities of α‐In₂Se₃crystals. Then, α‐In₂Se₃flakes are fabricated and used as a 2D ferroelectric semiconductor FET artificial synaptic device platform. By modulating the degree of polarization in α‐In₂Se₃flakes according to the gate electrical pulses, these devices exhibit distinct essential synaptic behaviors. Their synaptic performance shows excellent and robust reliability under repeated electrical pulses. Finally, it is demonstrated that the synaptic devices achieve an estimated learning accuracy of up to ≈87% for Modified National Institute of Standards and Technology patterns in a single‐layer neural network system. 

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