Enhanced Resistive Switching and Synaptic Characteristics of ALD Deposited AlN-Based RRAM by Positive Soft Breakdown Process

Nitride film played an essential role as an excellent diffusion barrier in the semiconductor field for several decades. In addition, interest in next-generation memories induced researchers’ attention to nitride film as a new storage medium. A Pt/AlN/TaN device was investigated for resistive random-access memory (RRAM) application in this work. Resistive switching properties were examined in the AlN thin film formed by atomic layer deposition (ALD). The unique switching feature conducted under the positive voltage was investigated, while the typical bipolar switching was conducted under the application of negative voltage. Good retention and DC, and pulse endurances were achieved in both conditions and compared to the memory performances. Finally, the electronic behaviors based on the unique switching feature were analyzed through X-ray photoelectron spectroscopy (XPS) and the current–voltage (I–V) linear fitting model

A Roundabout Approach to Control Morphological Orientation and Solar-Cell Performance by Modulating Side-Chain Branching Position in Benzodithiophene-Based Polymers

To be meaningful to guide the rational design of novel high-performance conjugated semiconductors, we prepared three benzo[1,2-b:4,5-b]dithiophene (BDT)-based polymers by systematically moving the branching point of the alkyl chain. The effect of side-chain engineering was thoroughly investigated by a range of techniques. We demonstrate that a subtle change in the branching position in the BDT core can have a critical impact on polymer packing and preferential backbone orientation in thin films; copolymers made from BDT and thieno[3,4-c]pyrrole-4,6-dione units (TPD) adopt more of a face-on orientation as the branching point is shifted closer to the backbone, which can be correlated with a dramatic difference in solar-cells performance. The high short-circuit current density (11.6 mAcm(-2)) for the copolymer with one carbon atom between the alkoxylated oxygen atom and the branching point results from its predominantly face-on orientation and smoother surface in thin films, which results in power conversion efficiencies as high as 4.56%.clos

Exploiting Ternary Blends to Accurately Control the Coloration of Semitransparent, Non-Fullerene, Organic Solar Cells

Semitransparent organic solar cells (STOSCs) have received increasing attention due to promising applications such as building-integrated photovoltaics. Successful commercialization requires that STOSCs are aesthetically pleasing as well as having balanced power conversion efficiencies (PCEs) and average visible transmittances (AVTs). Non-fullerene acceptors, which possess excellent electrical/chemical properties, have helped STOSCs to achieve high PCE and AVT; however, research related to modulating color and appearance of STOSCs has lagged behind. Herein, narrow bandgap donor and acceptor (PTB7-Th and IEICO-4F) and ultra-wide bandgap acceptors (T2-ORH and T2-OEHRH) are used to achieve semitransparency and controllable device coloration. Blend films with controllable colors including cyan -> blue -> purple -> reddish purple colors are successfully demonstrated, which are controlled by ratios of IEICO-4F:T2-ORH or IEICO-4F:T2-OEHRH with PTB7-Th. By incorporating semitransparent electrodes (comprising Sb2O3/Ag/Sb2O3), STOSCs with PCEs of 6-7% are achieved for cyan, aqua, indigo, and purple and approximate to 4% PCEs for reddish-purple colors, with AVTs in the range of 23-35%. Moreover, optical properties of blend films are studied via absorption and transmission measurements, whereas the range of colors achieved is quantified using commission internationale de l'eclairage (CIE) chromaticity and CIE L * a * b* color space then represented as RGB color models

Optically Tunable Plasmonic Two-Dimensional Ag Quantum Dot Arrays for Optimal Light Absorption in Polymer Solar Cells

The application of localized surface plasmon resonance (LSPR) phenomena is an effective strategy to enhance the performance of polymer solar cells (PSCs) because of their ability to efficiently scatter light and dramatically increase light absorption in the active layer of PSCs. Unlike previous reports investigating LSPR materials in PSCs, we have.approached the LSPR phenomenon from a physical perspective by examining the influence of the surrounding environment LSPR properties. Uniformly ordered two-dimensional 10 nm Ag quantiun dot arrays (2D Ag-QAs) were prepared and utilized in PSCs. The 2D Ag QAs were incoiliorated into-electron transport layers with different. efractive indices, which showed a significant liathochrornic shift as the, refractive index increased and excellent agreement with theoretical calculations taking intrinsic size effects, nonlocal response, and plasmon, coupling effects into account. When incorporated into PSCs, power conversion efficiencies of op to, 8.51% were realized a 12.5% enhancement compared to devices without Ag QAs

High-Performance Perovskite Quantum Dot Solar Cells Enabled by Incorporation with Dimensionally Engineered Organic Semiconductor

Perovskite quantum dots (PQDs) have been considered promising and effective photovoltaic absorber due to their superior optoelectronic properties and inherent material merits combining perovskites and QDs. However, they exhibit low moisture stability at room humidity (20-30%) owing to many surface defect sites generated by inefficient ligand exchange process. These surface traps must be re-passivated to improve both charge transport ability and moisture stability. To address this issue, PQD-organic semiconductor hybrid solar cells with suitable electrical properties and functional groups might dramatically improve the charge extraction and defect passivation. Conventional organic semicon-ductors are typically low-dimensional (1D and 2D) and prone to excessive self-aggregation, which limits chemical interaction with PQDs. In this work, we designed a new 3D star-shaped semiconducting material (Star-TrCN) to enhance the compatibility with PQDs. The robust bonding with Star-TrCN and PQDs is demonstrated by theoretical modeling and experimental validation. The Star-TrCN-PQD hybrid films show improved cubic-phase stability of CsPbI3-PQDs via reduced surface trap states and suppressed moisture penetration. As a result, the resultant devices not only achieve remarkable device stability over 1000 h at 20-30% relative humidity, but also boost power conversion efficiency up to 16.0% via forming a cascade energy band structure. © 2022, The Author(s).TRU

Order-disorder phase transition driven by interlayer sliding in lead iodides

A variety of phase transitions have been found in two-dimensional layered materials, but some of their atomic-scale mechanisms are hard to clearly understand. Here, we report the discovery of a phase transition whose mechanism is identified as interlayer sliding in lead iodides, a layered material widely used to synthesize lead halide perovskites. The low-temperature crystal structure of lead iodides is found not 2H polytype as known before, but non-centrosymmetric 4H polytype. This undergoes the order-disorder phase transition characterized by the abrupt spectral broadening of valence bands, taken by angle-resolved photoemission, at the critical temperature of 120 K. It is accompanied by drastic changes in simultaneously taken photocurrent and photoluminescence. The transmission electron microscopy is used to reveal that lead iodide layers stacked in the form of 4H polytype at low temperatures irregularly slide over each other above 120 K, which can be explained by the low energy barrier of only 10.6 meV/atom estimated by first principles calculations. Our findings suggest that interlayer sliding is a key mechanism of the phase transitions in layered materials, which can significantly affect optoelectronic and optical characteristics

Order-disorder phase transition driven by interlayer sliding in lead iodides

2D layered materials attract interest due to their potential for application in nanoelectronics and optoelectronics. Here authors report an order-disorder-type phase transition driven by temperature in bulk lead iodides, and interlayer sliding is identified to play a key role in the mechanism of this phase transition

Thiophene and Naphtho[1,2-c:5,6-c]bis[1,2,5]thiadiazole Based Alternating Copolymers for Polymer Solar Cells

Two planar type photovoltaic polymers based on naphthobisthiadiazole, poly(2,5-bis(2-hexyldecyloxy)phenylene-alt-(5,10-dithiophen-2-yl)naphtho [1,2-c :5,6-c]bis [1,2,5]thiadiazole) (h-PPDTNTz) and poly(2,5-bis(2-decyltetradecyloxy)phenylene-alt-(5,10-dithiophen-2-yl)naphtho [1,2-c:5,6-c]bis[1,2,5]thiadiazole) (d-PPDTNTz) were synthesized by incorporating intrachain noncovalent Coulombic interactions in the molecular design. To achieve a delicate balance of molecular weight, solubility as well as bulk film morphology, hexyldecyloxy (h-) and decyltetradecyloxy (d-) side-chains were substituted, which played a decisive role in modulating morphology, film packing structure and macroscopic device properties. Both polymers showed a broad light absorption up to similar to 800 nm and d-PPDTNTz exhibited a deeper HOMO and preferentially face-on orientation in pristine and blended films with PCIIBM. The detailed optical, electrochemical, thermal, morphological and the resulting photovoltaic characteristics were studied. The best power conversion efficiency of similar to 6.7% was measured for d-PPDTNTz:PC71BM, suggesting that the careful choice of side-chains is necessary for fully optimize the photovoltaic materials and devices.clos