Field-effect Solar Cells Research Articles

Imaging nanostructures in organic semiconductor films with scanning transmission X-ray spectro-microscopy

Thin films of organic semiconducting materials are of increasing technological importance in optoelectronic devices such as light emitting diodes (LEDs), lasers, field effect transistors (FETs) and solar cells. However, the morphology of such films is complex, often displaying three dimensional composition structure or molecular alignment effects. The structure of the polymer film incorporated into a device can strongly affect its performance characteristics, e.g. via the connectedness of polymer domains and to the device electrodes, or due to anisotropic material properties due to molecular alignment.Scanning transmission X-ray spectro-microscopy (STXM) has been demonstrated to be an excellent tool for the study of organic materials due to its high spatial resolution (down to about 20nm) and strong contrast based on a variety of spectroscopic mechanisms. In particular, tuning the probing X-ray beam to resonances in the near edge X-ray absorption fine structure (NEXAFS) spectra provides a mechanism for molecular-structure based contrast which is a very powerful tool for studying blends of organic components. A further advantage of STXM is that strategic use of spectroscopic information allows quantitative compositional analysis of imaged areas. Recent work at the PolLux STXM has demonstrated two new developments in the imaging of thin organic films: simultaneous surface and bulk imaging via an additional channeltron electron detector, and molecular orientation mapping via anisotropic near edge resonances.

Connecting Organic Nanowires

In this work we report on a universal methodology for connecting organic nanowires and nanosheets formed by p-conjugated molecules viametal nanoparticles. We present a brief study on the electrical characteristics of the thus connected nanowires carried out in a four-tip-STM manipulation and measurement system (4TMMS; STM1⁄4 scanning tunneling microscopy) under ultrahigh vacuum (UHV) conditions. The recent developments in organic semiconducting nanostructures have permitted important advances in the fabrication of low-cost, large-area, flexible optic and microelectronic devices. In fact, over the last few years the use of p-conjugated molecules as building blocks for such organic nanostructures has received special attention and interest. Within the class of p-conjugated molecules, the families of metallo porphyrins, metallo phthalocyanines, and perylenes are promising materials for varying applications such as vapor (gas) nanosensors and as active components for photonic devices, organic field effect transistors (OFETs), phototransistors, and solar cells. It has been realized that the fabrication of hybrid organic!inorganic materials comprising semiconducting organic nanowires and metal particles opens new routes in the design of devices’ functionality. Such hybrid materials may provide a ideal model system for the study of organic!inorganic nanomaterials. Despite this promising prospect, only very few works exist regarding the formation of organic semiconducting nanofibers!metal particles hybrid systems. ] In this Communication, we present a significant step forward in the fabrication of nanowire–metal–nanowire junctions by using metal nanoparticle-decorated organic nanowires as a base for the growth of secondary nanowires in such a way that a new route for the fabrication of connected organic single-crystal nanowires is demonstrated. First, we describe the organic/inorganic hybrid nanostructures prepared by decorating single-crystal organic nanowires with metal particles in a one-step dry process at room temperature. In a second step we demonstrate an unprecedented class of heterostructured nanowires formed by connection through metal nanoparticles of different organic nanostructures. Finally, the electrical conductivity of these connected nanowires is studied in a 4TMMS. Preparation of Hybrid and Connected Nanowires: Recently, we have reported a universal method for the growth of squared nanowires and nanobelts formed by p-conjugated molecules on

Mesostructured Hybrids Containing Potential Donors and Acceptors with Molecular-Scale and Meso-Scale Segregation and Ordering: Toward the Development of Smart Materials through Hierarchical Self-Assembly

A novel self-assembly approach was developed to design and synthesize innovative mesostructured hybrid materials with intimately contacted potential donor (D) and acceptor (A) domains organized in a three-dimensional ordering. Two specific organic and inorganic components, both of which bear optoelectronic functionalities (D and A, respectively), were designed and used. Then the one-step self-assembly process locks both D and A molecules into ordered three-dimensional nanostructure, which may allow for the uniform and molecular level controllable organization of the D and A molecules in the central regions of the pore channels and the pore walls of the hybrids, respectively. The optical properties were discussed in relation to the architectures of the materials, which offer an opportunity to disclose the distribution model of organic molecules within the mesostructured hybrids. Obviously, this hierarchical self-assembly of advanced architectures indicates that it should readily be possible to substitute the D and A for alternative different functional groups, which is of great importance toward the development of a family of smart materials for the purpose of constructing novel platforms for field effect transistors, solar cells, and other device applications.

Nanodevices Based on Silicon Nanowires

Silicon nanowires (SiNWs) have been demonstrated as one of the promising building blocks for future nanodevices such as field effect transistors, solar cells, sensors and lithium battery; much progress has been made in this field during last decades. In this review paper, the synthesis and physical properties of SiNWs are introduced briefly. Significant advances of SiNWs-related nanodevices reported in recent literature and registered patents are reviewed. The latest development and prospects of SiNWs-related nanodevices are also discussed.

Evidence of a high density of fixed negative charges in an insulation layer compound on silicon

For drift field generation, IS structures with a positive interface charge in an insulator compound were developed in the 1980s and employed mainly on field effect solar cells. While there has been a large number of publications about the positively biased insulator–semiconductor structure there has been very little interest in its antipolar counterpart — the negatively biased insulator–semiconductor structure — so far. However, by using that structure as a second drift field source for field effect solar cells their conversion efficiency could be improved. The conventional rear surface passivation of silicon active layers by shallow ultrahigh aluminium doping in order to form a back surface field involves a high density of lattice and surface defects which increase recombination rates. The structure introduced herein is put onto a silicon layer and acts thus as an external negative drift field source, thereby avoiding the drawbacks of ultrahigh doping. The layer arrangement aluminiumfluoride–silicon dioxide on silicon seems to be a good candidate for a negative drift field source. Experimental results which led to a fixed interface charge of up to −1.6×1012 cm−2 at the interface aluminiumfluoride∣∣silicon dioxide are presented and an interpretation of the fixed negative charge is given.

The negatively charged insulator-semiconductor structure: concepts, technological considerations and applications

The use of possibly uncharged and therefore passivated Insulator-Semiconductor structures (IS-structures) in conventional semiconductor devices as MISFETs is well known and has been an issue of many research papers. For drift field generation IS structures with a fixed positive interface charge in the insulator were developed in the 80 s and employed mainly as a part of field effect solar cells. While there has been a large number of publications about the positively biased IS structure there has been very little interest in its antipolar counterpart — the negatively biased IS structure — so far. In this paper we introduce theoretical considerations and qualitative models how such a structure would look and work like. Furthermore we consider technological aspects of producing a negatively biased IS structure. Possible applications are discussed as well. PACS code: 73.20, 68.35, 85.50, 85.30

Device simulation and fabrication of field effect solar cells

The performance of a novel hydrogenated amorphous silicon (a-Si : H) solar cell which utilizes the field effect solar cell (FESC) has been investigated both theoretically and experimentally. The theoretical analysis has been done for bothp- andn-channel FESCs by employing a two-dimensional device simulator which is based on current continuity and Poisson equations. The calculated performance is compared with that of conventional (p-i-n)a-Si : H solar cells. The calculation demonstrated that bothn-channel andp-channel FESCs could improve the conversion efficiency by as much as 50%.In order to check the reliability of simulation, the transport properties of intrinsica-Si : H film and thin film transistor (TFT) have also been calculated and compared with the experimentally obtained characteristics. Experimental verification of TFT and FESC has been attempted by using MgO anda-SiN : H as dielectric layer materials. Preliminary results are presented.

Organic Semiconductors for new electronic devices

Field effect transistors, schottky diodes, and solar cells are among the applications of organic semiconductors now being developed. Questions concerning charge generation and transport as well as doping mechanisms in these materials, which include polyacetylenes, polythiophenes and metallophthalocyanines are reviewed, and future directions in both experimental and theoretical work discussed.