Fossil fuel alternatives, such as solar energy, are moving to the forefront in a variety of research fields. Polymer-based organic photovoltaic systems hold the promise for a cost-effective, lightweight solar energy conversion platform, which could benefit from simple solution processing of the active layer. The function of such excitonic solar cells is based on photoinduced electron transfer from a donor to an acceptor. Fullerenes have become the ubiquitous acceptors because of their high electron affinity and ability to transport charge effectively. The most effective solar cells have been made from bicontinuous polymer–fullerene composites, or so-called bulk heterojunctions. The best solar cells currently achieve an efficiency of about 5 %, thus significant advances in the fundamental understanding of the complex interplay between the active layer morphology and electronic properties are required if this technology is to find viable application.

Polymer–Fullerene Composite Solar Cells

-phenylenevinylene)s L4. Fluorene-Based Conjugated Polymers L4.1. Fluorene-Based Copolymers ContainingElectron-Rich MoietiesM4.2. Fluorene-Based Copolymers ContainingElectron-Deﬁcient MoietiesN4.3. Fluorene-Based Copolymers ContainingPhosphorescent ComplexesQ5. Carbazole-Based Conjugated Polymers R5.1. Poly(2,7-carbazole)-Based Polymers R5.2. Indolo[3,2-

https://ir.nctu.edu.tw:443/bitstream/11536/6508/1/000271856900020.pdf

Synthesis of Conjugated Polymers for Organic Solar Cell Applications

2.2. Materials 929 2.3. Factors Influencing Charge Mobility 931 2.3.1. Molecular Packing 931 2.3.2. Disorder 932 2.3.3. Temperature 933 2.3.4. Electric Field 934 2.3.5. Impurities 934 2.3.6. Pressure 934 2.3.7. Charge-Carrier Density 934 2.3.8. Size/molecular Weight 935 3. The Charge-Transport Parameters 935 3.1. Electronic Coupling 936 3.1.1. The Energy-Splitting-in-Dimer Method 936 3.1.2. The Orthogonality Issue 937 3.1.3. Impact of the Site Energy 937 3.1.4. Electronic Coupling in Oligoacene Derivatives 938

Charge transport in organic semiconductors.

New polymer synthesis by nitroxide mediated living radical polymerizations.

Fabrication and processing of polymer solar cells: A review of printing and coating techniques

During the last decade the field of polymer photovoltaics has seen a tremendous improvement in both device efficiency and understanding of the underlying physical processes One has come to a point in which the prototypical large bandgap material system P3HT:PCBM is nearing optimal device performance In order to enhance efficiencies even further, research activities for new materials are needed with better aligned energy levels One interesting approach is by narrowing the donor bandgap to enhance light absorption Recent developments on small band gap (<20 eV) materials for photovoltaic applications are reviewed First, an introduction is given regarding the processes governing the exciton dissociation, charge transport requirements, energy level engineering of both donor and acceptor materials, and other parameters determining the photovoltaic performance The focus is on polymeric donor materials, which are subdivided by the type of monomeric units that constitute the backbone Finally, the synthetic

Small Bandgap Polymers for Organic Solar Cells (Polymer Material Development in the Last 5 Years)

The use of molecular electronics is a much-discussed alternative to conventional silicon devices: the prospect of such tiny components has obvious implications for miniaturization. One approach is to replace the conventional semiconductor with a single molecular layer that self-organizes between two electrodes. Molecular tunnel junctions have been made in such systems, but they tend to be hard to reproduce, unstable and limited to small diameters. Now Akkerman et al. have developed a relatively simple way of producing stable, reproducible molecular junctions with large areas from self-assembled monolayers of alkanethiols. The process is compatible with standard integrated circuit technologies and could offer a cheap way forward in the quest for practical molecular electronics. A relatively simple method to fabricate stable, reproducible molecular junctions with large areas from self-assembled monolayers of alkanethiols has been developed — this approach could offer a cheap and promising way forward for molecular electronics. Electronic transport through single molecules has been studied extensively by academic1,2,3,4,5,6,7,8 and industrial9,10 research groups. Discrete tunnel junctions, or molecular diodes, have been reported using scanning probes11,12, break junctions13,14, metallic crossbars6 and nanopores8,15. For technological applications, molecular tunnel junctions must be reliable, stable and reproducible. The conductance per molecule, however, typically varies by many orders of magnitude5. Self-assembled monolayers (SAMs) may offer a promising route to the fabrication of reliable devices, and charge transport through SAMs of alkanethiols within nanopores is well understood, with non-resonant tunnelling dominating the transport mechanism8. Unfortunately, electrical shorts in SAMs are often formed upon vapour deposition of the top electrode16,17,18, which limits the diameter of the nanopore diodes to about 45 nm. Here we demonstrate a method to manufacture molecular junctions with diameters up to 100 µm with high yields (> 95 per cent). The junctions show excellent stability and reproducibility, and the conductance per unit area is similar to that obtained for benchmark nanopore diodes. Our technique involves processing the molecular junctions in the holes of a lithographically patterned photoresist, and then inserting a conducting polymer interlayer between the SAM and the metal top electrode. This simple approach is potentially low-cost and could pave the way for practical molecular electronics.

/pdf/towards-molecular-electronics-with-large-area-molecular-1l9mb3pfyj.pdf

Towards molecular electronics with large-area molecular junctions

A memory functionality is a prerequisite for many applications of electronic devices. Organic nonvolatile memory devices based on ferroelectricity are a promising approach toward the development of a low-cost memory technology. In this Review Article we discuss the latest developments in this area with a focus on three of the most important device concepts: ferroelectric capacitors, field-effect transistors, and diodes. Integration of these devices into larger memory arrays is also discussed.

/pdf/organic-nonvolatile-memory-devices-based-on-ferroelectricity-2ztx79zkp4.pdf

Organic Nonvolatile Memory Devices Based on Ferroelectricity

Self-assembly—the autonomous organization of components into patterns and structures1—is a promising technology for the mass production of organic electronics. Making integrated circuits using a bottom-up approach involving self-assembling molecules was proposed2 in the 1970s. The basic building block of such an integrated circuit is the self-assembled-monolayer field-effect transistor (SAMFET), where the semiconductor is a monolayer spontaneously formed on the gate dielectric. In the SAMFETs fabricated so far, current modulation has only been observed in submicrometre channels3–5, the lack of efficient charge transport in longer channels being due to defects and the limited intermolecular p–p coupling between the molecules in the selfassembled monolayers. Low field-effect carrier mobility, low yield and poor reproducibility have prohibited the realization of bottom-up integrated circuits. Here we demonstrate SAMFETs with long-range intermolecular p–p coupling in the monolayer. We achieve dense packing by using liquid-crystalline molecules consisting of a p-conjugated mesogenic core separated by a long aliphatic chain from a monofunctionalized anchor group. The resulting SAMFETs exhibit a bulk-like carrier mobility, large current modulation and high reproducibility. As a first step towards functional circuits, we combine the SAMFETs into logic gates as inverters; the small parameter spread then allows us to combine the inverters into ring oscillators. We demonstrate real logic functionality by constructing a 15-bit code generator in which hundreds of SAMFETs are addressed simultaneously. Bridging the gap between discrete monolayer transistors and functional selfassembled integrated circuits puts bottom-up electronics in a new perspective.

/pdf/bottom-up-organic-integrated-circuits-2xv3lud7i5.pdf

Bottom-up organic integrated circuits

Although research on molecular electronics has drawn increasingly more attention in the last decade, the large spread in obtained results for the conduction rescaled to a single molecule indicates a strong dependence of the measured data on the experimental testbed used. We subdivided a generalized metal-molecule-metal junction into different components and discuss their influence on electrical transport measurements of a single organic molecule or an assembly of molecules. By relating the advantages and disadvantages of different experimental testbeds to the more general view of a molecular junction, we strive to explain the discrepancies between the obtained results on molecular conduction. The reported results on molecular conduction of molecules with an alkane backbone can be categorized into three groups with different resistance values, depending on the device area of the molecular junction and the nature of the contacts.

/pdf/electrical-conduction-through-single-molecules-and-self-pi731fusu0.pdf

Bert de Boer

Papers

Small Bandgap Polymers for Organic Solar Cells (Polymer Material Development in the Last 5 Years)

Towards molecular electronics with large-area molecular junctions

Organic Nonvolatile Memory Devices Based on Ferroelectricity

Bottom-up organic integrated circuits

Electrical conduction through single molecules and self-assembled monolayers