The major efforts in solar energy research are currently directed at developing cost-effective systems for energy conversion and storage. [1][2][3] The high cost of materials and preparation methods that are required for the fabrication of inorganic solar cells prevent their widespread deployment. Seeking a low-cost alternative in the form of solution-processable or roll-to-roll printable organic solar cells features prominently in the energy research roadmap. The conventional anode of choice for organic solar cells has been indium tin oxide (ITO), which consumes as much as 30% of the fabrication cost in solar cells. High quality ITO is expensive due to the dwindling supplies of indium. ITO also suffers from drawbacks like brittleness, sensitivity to acids and bases during processing, and reactive interface formation with copper indium sulfi de during high-temperature sintering. Graphene fi lms have been proposed as the new generation of multifunctional, transparent, and conducting electrodes. The attractiveness of graphene arises from their low cost, transparency, high electrical conductivity, chemical robustness, and fl exibility, as opposed to the rising cost and brittleness of ITO. [4][5][6] In particular, the 2D graphene sheet is emerging as a possible substitute for ITO in fl exible displays, touch screens, and solar cells. [7][8][9] The sheet resistance of graphene is given by Rs = (F 2D N) −1 where F 2D is the 2D sheet conductivity and N is the number of layers. The intrinsic sheet resistance of single layer graphene is calculated to be ≈ 6 k Ω and is inferior to that of ITO (10-20 Ω sq − 1 ). [ 10 ] In principle, increasing the thickness (increasing N ) of graphene using layer-by-layer stacking and doping the graphene (increasing F 2D by increasing the carrier concentration) can allow the extrinsic sheet resistance values to be reduced to as low as 20 Ω sq − 1 although it is not trivial to reach this limit at present. [ 10 ] Many are excited about the transparency and conductivity of multilayered graphene fi lms, however the ultimate performance of graphene in solar cells may be limited by other factors. First, the interfacial energy offset between graphene and the photoactive materials has to be tuned in order to optimize charge transfer. Second, the planarity and hydrophilic character of multilayer graphene has to be improved to allow for spin-coating with hole-transporting layers such as poly(3,4-ethylenedioythiophene):poly (styrenesulfonate) (PEDOT:PSS). Third, the preparation of the graphene fi lms has to be improved in terms of achieving large grain crystal growth, as well as reducing contaminations from organic residues in the transfer process. The organic residues have a deleterious effect on the conductivity, transparency, and roughness of graphene fi lms. To date, there have been no reports that graphene can exhibit a power conversion effi ciency (PCE) higher than ITO when replacing the latter in solar cell devices. [ 11 ] This underscores the diffi culty in optimizing any factors in the fabric...

Two-terminal resistive switching devices are commonly plagued with longstanding scientific issues including interdevice variability and sneak current that lead to computational errors and high-power consumption. This necessitates the integration of a separate selector in a one-transistor-one-RRAM (1T-1R) configuration to mitigate crosstalk issue, which compromises circuit footprint. Here, we demonstrate a multiterminal memtransistor crossbar array with increased parallelism in programming via independent gate control, which allows in situ computation at a dense cell size of 3−4.5 F 2 and a minimal sneak current of 0.1 nA. Moreover, a low switching energy of 20 fJ/bit is achieved at a voltage of merely 0.42 V. The architecture is capable of performing multiply-and-accumulate operation, a core computing task for pattern classification. A high MNIST recognition accuracy of 96.87% is simulated owing to the linear synaptic plasticity. Such computing paradigm is deemed revolutionary toward enabling data-centric applications in artificial intelligence and Internet-of-things.

Single-layer molybdenum disulfide (MoS) has attracted significant attention due to its electronic and physical properties, with much effort invested toward obtaining large-area high-quality monolayer MoS films. In this work, we demonstrate a reactive-barrier-based approach to achieve growth of highly homogeneous single-layer MoS on sapphire by the use of a nickel oxide foam barrier during chemical vapor deposition. Due to the reactivity of the NiO barrier with MoO, 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 MoS monolayer.