Enhancing Ion Migration in Grain Boundaries of Hybrid Organic–Inorganic Perovskites by Chlorine

Ionicity plays an important role in determining material properties, as well as optoelectronic performance of organometallic trihalide perovskites (OTPs). Ion migration in OTP films has recently been under intensive investigation by various scanning probe microscopy (SPM) techniques. However, controversial findings regarding the role of grain boundaries (GBs) associated with ion migration are often encountered, likely as a result of feedback errors and topographic effects common in to SPM. In this work, electron microscopy and spectroscopy (scanning transmission electron microscopy/electron energy loss spectroscopy) are combined with a novel, open‐loop, band‐excitation, (contact) Kelvin probe force microscopy (BE‐KPFM and BE‐cKPFM), in conjunction with ab initio molecular dynamics simulations to examine the ion behavior in the GBs of CH₃NH₃PbI₃ perovskite films. This combination of diverse techniques provides a deeper understanding of the differences between ion migration within GBs and interior grains in OTP films. This work demonstrates that ion migration can be significantly enhanced by introducing additional mobile Cl^? ions into GBs. The enhancement of ion migration may serve as the first step toward the development of high‐performance electrically and optically tunable memristors and synaptic devices.     

Fault-Tolerant Mesh-Based NoC with Router-Level Redundancy

The aggressively scaled CMOS technology is increasingly threatening the dependability of network-on-chips (NoCs) architecture. In a mesh-based NoC, a faulty router or broken link may isolate a well functional processing element (PE). Also, a set of faulty routers may form isolated regions, which can degrade the design. In this paper, we propose a router-level redundancy (RLR) fault-tolerant scheme that differs from the traditional microarchitecture-level redundancy (MLR) approach to relieve the problem of isolated PE and isolated region. By simply adding one spare router within each router set in a mesh, RLR can be created and connection paths between adjacent routers can be diversified. To exploit this extra resource, two reconfiguration algorithms are demonstrated to detour observed faulty routers/links. The proposed RLR fault-tolerant scheme can tolerate at most one faulty router within a router set. After the reconfiguration, the original mesh topology is maintained. As a result, the proposed architecture does not need any support from the network layer routing algorithms. The scheme has been evaluated based on the three fault-tolerant metrics: reliability, mean time to failure (MTTF), and yield. The experimental results show that the performance RLR increases as the size of NoC grows; however, the relative connection cost decreases at the same time. This characteristic makes our architecture suitable for large-scale NoC designs.

     

A Versatile Fluoro‐Containing Low‐Bandgap Polymer for Efficient Semitransparent and Tandem Polymer Solar Cells

The versatility of a fluoro‐containing low band‐gap polymer, poly[2,6‐(4,4‐bis(2‐ethylhexyl)‐4H‐cyclopenta[2,1‐b;3,4‐b’]dithiophene)‐alt‐4,7‐(5‐fluoro‐2,1,3‐benzothia‐diazole)] (PCPDTFBT) in organic photovoltaics (OPVs) applications is demonstrated. High boiling point 1,3,5‐trichlorobenzene (TCB) is used as a solvent to manipulate PCPDTFBT:[6,6]‐phenyl‐C₇₁‐butyric acid methyl ester (PC₇₁BM) active layer morphology to obtain high‐performance single‐junction devices. It promotes the crystallization of PCPDTFBT polymer, thus improving the charge‐transport properties of the active layer. By combining the morphological manipulation with interfacial optimization and device engineering, the single‐junction device exhibits both good air stability and high power‐conversion efficiency (PCE, of 6.6%). This represents one of the highest PCE values for cyclopenta[2,1‐b;3,4‐b’]dithiophene (CPDT)‐based OPVs. This polymer is also utilized for constructing semitransparent solar cells and double‐junction tandem solar cells to demonstrate high PCEs of 5.0% and 8.2%, respectively.     

Boosting Infrared Light Harvesting by Molecular Functionalization of Metal Oxide/Polymer Interfaces in Efficient Hybrid Solar Cells

Hybrid solar cells based on light absorbing semiconducting polymers infiltrated in nanocrystalline TiO₂ electrodes, have emerged as an attractive concept, combining benefits of both low material and processing costs with well controlled nano‐scale morphology. However, after over ten years of research effort, power conversion efficiencies remain around 0.5%. Here, a spectroscopic and device based investigation is presented, which leads to a new optimization route where by functionalization of the TiO₂ surface with a molecular electron acceptor promotes photoinduced electron transfer from a low‐band gap polymer(poly[2,6‐(4,4‐bis‐(2‐ethylhexyl)‐4H‐cyclopenta[2,1‐b;3,4‐b0]dithiophene)‐alt‐4,7‐(2,1,3‐benzothiadia‐zole)] (PCPDTBT) to the metal oxide. This boosts the infrared response and the power conversion efficiency to over 1%. As a further step, by “co‐functionalizing” the TiO₂ surface with the electron acceptor and an organic dye‐sensitizer, panchromatic spectral photoresponse is achieved in the visible to near‐IR region. This novel architecture at the heterojunction opens new material design possibilities and represents an exciting route forward for hybrid photovoltaics.     

Low operational voltage and high performance organic field effect memory transistor with solution processed graphene oxide charge storage media

Low voltage organic field effect memory transistors are demonstrated by adapting a hybrid gate dielectric and a solution processed graphene oxide charge trap layer. The hybrid gate dielectric is composed of aluminum oxide (AlO_x) and [8-(11-phenoxy-undecyloxy)-octyl]phosphonic acid (PhO-19-PA) plays an important role of both preventing leakage current from gate electrode and providing an appropriate surface energy to allow for uniform spin-casting of graphene oxide (GO). The hybrid gate dielectric has a breakdown voltage greater than 6 V and capacitance of 0.47 μF/cm². Graphene oxide charge trap layer is spin-cast on top of the hybrid dielectric and has a resulting thickness of approximately 9 nm. The final device structure is Au/Pentacene/PMMA/GO/PhO-19-PA/AlO_x/Al. The memory transistors clearly showed a large hysteresis with a memory window of around 2 V under an applied gate bias from 4 V to −5 V. The stored charge within the graphene oxide charge trap layer was measured to be 2.9 × 10¹² cm⁻². The low voltage memory transistor operated well under constant applied gate voltage and time with varying programming times (pulse duration) and voltage pulses (pulse amplitude). In addition, the drain current (I_ds) after programming and erasing remained in their pristine state after 10⁴ s and are expected to be retained for more than one year.     

Diagrammatic Separation of Different Crystal Structures of A2BX4 Compounds Without Energy Minimization: A Pseudopotential Orbital Radii Approach

The A₂BX₄ family of compounds manifest a wide range of physical properties, including transparent conductivity, ferromagnetism, and superconductivity. A 98% successful diagrammatic separation of the 44 different crystal structures of 688 oxide A₂BX₄ compounds (96% for 266 oxide‐only) is described by plotting the total radius of the A atom R_A versus the radius of the B atom R_B for many A₂BX₄ compounds of known structure types and seeking heuristically simple, straight boundaries in the R_A versus R_B plane that best separate the domains of different structure types. The radii are sums R_A = R_s(A) + R_p(A) of the quantum‐mechanically calculated “orbital radii” R_s(R_p), rather than empirical radii or phenomenological electronegativity scales. These success rates using first‐principles orbital radii uniformly exceed the success rates using classic radii. Such maps afford a quick guess of the crystal structure of a yet unmade A₂BX₄ compound by placing its atomic orbital radii on such maps and reading off its structure type.     

Interface Engineering for Organic Electronics

The field of organic electronics has been developed vastly in the past two decades due to its promise for low cost, lightweight, mechanical flexibility, versatility of chemical design and synthesis, and ease of processing. The performance and lifetime of these devices, such as organic light‐emitting diodes (OLEDs), photovoltaics (OPVs), and field‐effect transistors (OFETs), are critically dependent on the properties of both active materials and their interfaces. Interfacial properties can be controlled ranging from simple wettability or adhesion between different materials to direct modifications of the electronic structure of the materials. In this Feature Article, the strategies of utilizing surfactant‐modified cathodes, hole‐transporting buffer layers, and self‐assembled monolayer (SAM)‐modified anodes are highlighted. In addition to enabling the production of high‐efficiency OLEDs, control of interfaces in both conventional and inverted polymer solar cells is shown to enhance their efficiency and stability; and the tailoring of source–drain electrode–semiconductor interfaces, dielectric–semiconductor interfaces, and ultrathin dielectrics is shown to allow for high‐performance OFETs.