Chemically Doped Radial Junction Characteristics in Silicon Nanowires

We evaluate the boron (B) and phosphorus (P) core-surface codoped radial <i>p</i>–<i>n</i> junction characteristics in silicon nanowires (SiNWs) using density functional theory calculations. We find that the formation of radial <i>p</i>–<i>n</i> junction is energetically favorable. The stability depends on the diameter of SiNWs and the dopant concentration. Generally, a higher concentration of B–P pair dopants results in a more stable nanowire. More importantly, we predict that the radial <i>p</i>–<i>n</i> junction can evolve into a Schottky-like junction in relatively highly doped SiNWs when the diameter increases, attributing to the change of the core <i>p</i>-doping characteristic, that is, the core <i>p</i>-junction becomes metallic, while the <i>n</i>-junction near the surface remains semiconducting. The interfacial contact between the junctions is found to be the key for such change. Our calculated results support an experimental observation in SiNW solar cells

Thermally Stable Mesoporous Perovskite Solar Cells Incorporating Low-Temperature Processed Graphene/Polymer Electron Transporting Layer

In the short time since its discovery, perovskite solar cells (PSCs) have attained high power conversion efficiency but their lack of thermal stability remains a barrier to commercialization. Among the experimentally accessible parameter spaces for optimizing performance, identifying an electron transport layer (ETL) that forms a thermally stable interface with perovskite and which is solution-processable at low-temperature will certainly be advantageous. Herein, we developed a mesoporous graphene/polymer composite with these advantages when used as ETL in CH₃NH₃PbI₃ PSCs, and a high efficiency of 13.8% under AM 1.5G solar illumination could be obtained. Due to the high heat transmission coefficient and low isoelectric point of mesoporous graphene-based ETL, the PSC device enjoys good chemical and thermal stability. Our work demonstrates that the mesoporous graphene-based scaffold is a promising ETL candidate for high performance and thermally stable PSCs

Thermally Stable Mesoporous Perovskite Solar Cells Incorporating Low-Temperature Processed Graphene/Polymer Electron Transporting Layer

In the short time since its discovery, perovskite solar cells (PSCs) have attained high power conversion efficiency but their lack of thermal stability remains a barrier to commercialization. Among the experimentally accessible parameter spaces for optimizing performance, identifying an electron transport layer (ETL) that forms a thermally stable interface with perovskite and which is solution-processable at low-temperature will certainly be advantageous. Herein, we developed a mesoporous graphene/polymer composite with these advantages when used as ETL in CH₃NH₃PbI₃ PSCs, and a high efficiency of 13.8% under AM 1.5G solar illumination could be obtained. Due to the high heat transmission coefficient and low isoelectric point of mesoporous graphene-based ETL, the PSC device enjoys good chemical and thermal stability. Our work demonstrates that the mesoporous graphene-based scaffold is a promising ETL candidate for high performance and thermally stable PSCs

Interfacial Engineering of Metal-Organic Framework-Based Electrode for High-Performance Smart Glass

Prussian blue (PB), a representative metal–organic framework, holds great promise as an electrode material for optical applications. However, the preparation of cycle-stable PB with minimal defects/vacancies and coordinated water has been limited by the uncontrollable growth kinetics. Here, we report on the electrodeposition of a cycle-stable PB film via presilanization on the growth substrate. By self-assembling an aminosilane layer on the indium–tin oxide (a-ITO) substrate before the PB growth, we demonstrate an a-ITO/PB film with minimal defects/vacancies and water (∼5%), as validated by a combination of X-ray photoelectron spectroscopy (XPS), Raman and thermogravimetric analysis (TGA) studies. In addition, scanning electron microscopy (SEM) measurements indicate that the conventional delamination and cracking issue of the PB film can be effectively impeded in our a-ITO/PB film over 1000 cycles. The cyclic tests also indicate that the a-ITO/PB film attains a remarkably higher charge density of 17.4 mC/cm2 with better stability (charge density retention ∼87% over 1000 cycles) than the state-of-the-art PB benchmark. The crucial role of the aminosilane treatment in increasing the a-ITO/PB interaction/binding is elucidated by density functional theory (DFT) simulations. DFT results suggest that there is a substantial charge redistribution localized around the interface of a-ITO/PB, leading to six times increment in binding energy as compared to non-treated ITO/PB. As an exemplified application, the cycle-stable a-ITO/PB film is applied as an efficient counter electrode in a smart glass. This study paves an effective interfacial engineering means for increasing the binding at the PB–substrate interface and structural integrity of PB itself for long-term electrochemical and optical applications

Engineering Heterostructured Semiconductor Nanorod Assemblies via Controlled Cation Exchange: Implications for Efficient Optoelectronics

Precise control over the composition of heterostructure nanocrystals and their self-assembly is an emerging research interest. Superstructures of this type are typically enhanced in terms of their collective functionalities. Herein, we developed a practical yet simple approach to synthesize and self-assemble Cu2–xS/CuYS (Y = In, Sb, and Sn) heterostructured nanorods (NRs) into their vertically standing up assemblies. First NRs come together via depletion–attraction forces, and then partial cation exchange between Cu31S16 NRs and the injected cationic precursor taken in stoichiometric amounts dissolved in trioctylphosphine and oleylamine (Olam) results in heterostructured NRs possessing compositions of Cu2–xS/CuYS (Y = In, Sb, and Sn). The chemical composition changes lead to surface chemistry modifications as the injected guest cationic part of the NR is either naked or covered with Olam which is quite easy to strip-off from the NC surface at high temperature, resulting in a 2D sheetlike structure of heterostructured vertically oriented NRs in solution. The route to obtaining long-range heterostructured assembled NRs is studied and characterized systematically. This work presents a detailed mechanistic insight into the cation exchange-induced self-assembly of heterostructured NRs, where the particles are coupled, which is of growing importance as a synthesis tool. The complex nanostructures synthesized in the present work may benefit solution-processed optoelectronic applications

Modification of Vapor Phase Concentrations in MoS₂ Growth Using a NiO Foam Barrier

Single-layer molybdenum disulfide (MoS₂) has attracted significant attention due to its electronic and physical properties, with much effort invested toward obtaining large-area high-quality monolayer MoS₂ films. In this work, we demonstrate a reactive-barrier-based approach to achieve growth of highly homogeneous single-layer MoS₂ on sapphire by the use of a nickel oxide foam barrier during chemical vapor deposition. Due to the reactivity of the NiO barrier with MoO₃, the concentration of precursors reaching the substrate and thus nucleation density is effectively reduced, allowing grain sizes of up to 170 μm and continuous monolayers on the centimeter length scale being obtained. The quality of the monolayer is further revealed by angle-resolved photoemission spectroscopy measurement by observation of a very well resolved electronic band structure and spin–orbit splitting of the bands at room temperature with only two major domain orientations, indicating the successful growth of a highly crystalline and well-oriented MoS₂ monolayer