Dye-sensitized solar cells (DSCs) offer the possibilities to design solar cells with a large flexibility in shape, color, and transparency. DSC research groups have been established around the worl ...

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Dye-Sensitized Solar Cells

Many metal–insulator–metal systems show electrically induced resistive switching effects and have therefore been proposed as the basis for future non-volatile memories. They combine the advantages of Flash and DRAM (dynamic random access memories) while avoiding their drawbacks, and they might be highly scalable. Here we propose a coarse-grained classification into primarily thermal, electrical or ion-migration-induced switching mechanisms. The ion-migration effects are coupled to redox processes which cause the change in resistance. They are subdivided into cation-migration cells, based on the electrochemical growth and dissolution of metallic filaments, and anion-migration cells, typically realized with transition metal oxides as the insulator, in which electronically conducting paths of sub-oxides are formed and removed by local redox processes. From this insight, we take a brief look into molecular switching systems. Finally, we discuss chip architecture and scaling issues.

http://chialvo.org/Curso/UBACurso/DIA7/Papers/Aono_NatMat_07_Ionic%20Switching%20Memory.pdf

Nanoionics-based resistive switching memories

Nanocrystals (NCs) discussed in this Review are tiny crystals of metals, semiconductors, and magnetic material consisting of hundreds to a few thousand atoms each. Their size ranges from 2-3 to about 20 nm. What is special about this size regime that placed NCs among the hottest research topics of the last decades? The quantum mechanical coupling * To whom correspondence should be addressed. E-mail: dvtalapin@uchicago.edu. † The University of Chicago. ‡ Argonne National Lab. Chem. Rev. 2010, 110, 389–458 389

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Prospects of Colloidal Nanocrystals for Electronic and Optoelectronic Applications

Core/Shell Nanoparticles: Classes, Properties, Synthesis Mechanisms, Characterization, and Applications

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Metal–Organic Frameworks and Self-Assembled Supramolecular Coordination Complexes: Comparing and Contrasting the Design, Synthesis, and Functionality of Metal–Organic Materials

A simple process has been developed to create large area, highly uniform microporous thin films. Multilayers of weak polyelectrolytes were assembled onto silicon substrates by the sequential adsorption of poly(acrylic acid) and poly(allylamine) from aqueous solution. These multilayers were then immersed briefly into acidic solution (pH ≈ 2.4) to effect a substantial and irreversible transformation of the film morphology. The resulting microporous structures are 2−3 times the thickness of the original films, possess a correspondingly reduced relative density of 1/2 to 1/3, and are stable against further rearrangement under ambient conditions. In addition, the microporous films may undergo a secondary reorganization in neutral water, leading to a morphology with more discrete throughpores. A mechanism is proposed for these transformations based on interchain ionic bond breakage and reformation in this highly protonating environment, leading to an insoluble precipitate on the substrate which undergoes spinod...

Fabrication of Microporous Thin Films from Polyelectrolyte Multilayers

In this work, we introduce Cu2O thin films as a hole-transport layer in planar perovskite solar cells. Here, a Cu2O layer was formed through successive ionic layer adsorption and reaction (SILAR) method. With methylammonium lead triiodide (MAPbI3) we form a direct structure (p–i–n), where the perovskite layer is sandwiched between a layer of p-type Cu2O and another layer of n-type PCBM (phenyl-C61-butyric acid methyl ester), which acted as hole- and electron-transport materials, respectively. We locate band edges of the materials with respect to their Fermi energy by recording scanning tunneling spectroscopy that has correspondence to their density of states (DOS). We observe that the energy levels of the materials form type II band alignments at each of the two interfaces (p–i and i–n) for charge separation and uninterrupted carrier transport upon illumination. Such a band alignment enabled charge transfer from MAPbI3 as evidenced from quenching of its photoluminescence emission when the perovskite was i...

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Introducing Cu2O Thin Films as a Hole-Transport Layer in Efficient Planar Perovskite Solar Cell Structures

Vertically aligned ZnO nanowire arrays in Rose Bengal-based dye-sensitized solar cells

We have introduced functionalized multiwalled carbon nanotubes (CNTs) in donor/acceptor-type photovoltaic devices. We fabricated the devices based on heterostructure between polymer-CNT composite and buckminsterfullerene (C60) layers. Due to the functional groups of the CNTs, a homogeneous blend of CNT-polymer composite could be obtained. In the composite, the nanotubes acted as exciton dissociation sites and also hopping centers for hole transport. The CNTs in the polymer-CNT∕C60 device provided higher exciton dissociation volume and increased mobility for carrier transport. We have observed an increase in open-circuit voltage and short-circuit current in the polymer-CNT∕C60 devices as compared to the polymer∕C60 ones.

Functionalized carbon nanotubes in donor/acceptor-type photovoltaic devices

We have observed a large electrical conductance switching (ON:OFF ratio=105) in single-layer sandwich structures based on organic molecules at room temperature. The switching devices showed an associated memory effect for data-storage applications. We could write or erase a state and read it for many cycles. In switching devices, the active semiconductor retained its high conducting state until a reverse voltage erased it. A high conducting state arose due to restoration of conjugation in the molecule via electroreduction. Such a high ON–OFF ratio in a single layer sandwich structure, as compared to contemporary switching devices, is due to low off-state leakage current. The concept of conjugation restoration has been verified in supramolecular structures by adding donor groups to the molecule, which resulted in increased off-state current and hence lower ON–OFF ratio. Our work set a generalized example of selecting organic molecules to obtain higher ON–OFF ratio in molecular switching devices.

Amlan J. Pal

Papers

Fabrication of Microporous Thin Films from Polyelectrolyte Multilayers

Introducing Cu2O Thin Films as a Hole-Transport Layer in Efficient Planar Perovskite Solar Cell Structures

Vertically aligned ZnO nanowire arrays in Rose Bengal-based dye-sensitized solar cells

Functionalized carbon nanotubes in donor/acceptor-type photovoltaic devices

Large conductance switching and memory effects in organic molecules for data-storage applications