Important parameters of an organic semiconductor material are the electronic band gap (Eg) and the position of highest occupied and lowest unoccupied bands versus vacuum. These bands are called ...valence and conduction band for inorganic semiconductors. For organic semiconductors the bands defining the band gap are often called highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO). One advantage of semiconducting polymers is the ability to tune the band gap and the position of HOMO and LUMO levels by molecular chemical design. The organic photovoltaic solar cells need absorbers with a smaller bandgap to maximize the power conversion efficiency of these devices. There are several chemical strategies to synthesize low band gap polymers for optoelectronic applications. In this manuscript, an updated overview on the current status of these low band gap conjugated polymers will be given. The design principles of low band gap polymers, the properties of the resulting materials, and important applications and devices realized with this material class will be briefly discussed.
In contrast to inorganic semiconductors, modifications of the chemical structure can lead to large changes in the optical band gap of the organic polymeric semiconductor. In this manuscript, an updated overview on the design principles of low band gap semiconducting polymers, the properties of the resulting materials, and important applications and devices realized with these materials, are presented.
Indigo and its derivatives are dyes and pigments with a long and distinguished history in organic chemistry. Recently, applications of this ‘old’ structure as a functional organic building block for ...organic electronics applications have renewed interest in these molecules and their remarkable chemical and physical properties. Natural‐origin indigos have been processed in fully bio‐compatible field effect transistors, operating with ambipolar mobilities up to 0.5 cm2/Vs and air‐stability. The synthetic derivative isoindigo has emerged as one of the most successful building‐blocks for semiconducting polymers for plastic solar cells with efficiencies > 5%. Another isomer of indigo, epindolidione, has also been shown to be one of the best reported organic transistor materials in terms of mobility (∼2 cm2/Vs) and stability. This progress report aims to review very recent applications of indigoids in organic electronics, but especially to logically bridge together the hereto independent research directions on indigo, isoindigo, and other materials inspired by historical dye chemistry: a field which was the root of the development of modern chemistry in the first place.
Indigo and its derivatives are natural‐origin molecules with a long history, and have been at the center of the development of modern chemistry. Today, these substances are making a come‐back in the field of organic electronics.
•Electrocatalysis of O2 reduction in solution often requires special electrode materials.•Our subtraction method allows electrochemical analysis with conventional GC/Pt RRDE.•Information about excess ...current and excess efficiency can be provided.•Upon rotation the excess current and electrocatalytic potentials are affected.
The state-of-the-art procedure for investigating homogenous and heterogeneous electrocatalysts is cyclic voltammetry (CV). However, this technique usually requires an inactive electrode material. One common problem arising e. g. in studying the oxygen reduction reaction (ORR) is the significant background contribution to the overall ORR current provided by many carbon-based and metal-based electrode materials. Furthermore, rotating ring-disc electrodes (RRDEs) made of common materials like glassy carbon/platinum (GC/Pt) can be affected by overlapping reduction potentials on the disc. Interference from overlapping reactions on the ring might also occur, particularly in connection with oxygen reduction and hydrogen peroxide oxidation in ORR studies.
We present herein a novel subtraction method which allows a semi-quantitative description of homogeneous electrocatalysts and helps to overcome the overlapping problems described above using anthraquinone-2-sulfonate (AQS) as a “case study material” for the ORR.
We demonstrate ultrathin (2 µm thick) red and orange polymer light-emitting diodes with unprecedented mechanical properties in terms of their flexibility and ability to be stretched. The devices have ...a luminance greater than 100 cd m-2 , sufficient for a variety of optoelectronic applications including indoor displays. They can be operated as free-standing ultrathin films, allowing for crumpling during device operation. Furthermore, they may be applied to almost any surface whether rigid or elastomeric, and can withstand the associated mechanical deformation. They are shown to be extremely flexible, with radii of curvature under 10 µm, and stretch-compatible to 100% tensile strain. Such ultrathin light-emitting foils constitute an important step towards integration with malleable materials like textiles and artificial skin.
Research and development towards high efficiency plastic solar cells have been accelerating in recent years. Polymer-based bulk heterojunction solar cells are offering an attractive and inexpensive ...concept for large scale production by solution processing as well as advantageous flexible and aesthetic form factors. The thin film nano-morphology of bulk-heterojunction solar cells has been shown to dramatically influence the photovoltaic performance of the devices. This article reviews the different methods used to control the film nano-morphology of bulk-heterojunction solar cells focussing on the chemical additives during solution processing. All power conversion efficiency limiting mechanisms of bulk-heterojunction solar cells are discussed in detail. It is shown, how the formation of optimal percolation pathways between donor and acceptor influences the photovoltaic device performance. It is explained how the film nano-morphology relates to light absorption, free charge carrier generation as well as charge transport to the electrodes.
Successful formation of electronic interfaces between living cells and semiconductors hinges on being able to obtain an extremely close and high surface-area contact, which preserves both cell ...viability and semiconductor performance. To accomplish this, we introduce organic semiconductor assemblies consisting of a hierarchical arrangement of nanocrystals. These are synthesised via a colloidal chemical route that transforms the nontoxic commercial pigment quinacridone into various biomimetic three-dimensional arrangements of nanocrystals. Through a tuning of parameters such as precursor concentration, ligands and additives, we obtain complex size and shape control at room temperature. We elaborate hedgehog-shaped crystals comprising nanoscale needles or daggers that form intimate interfaces with the cell membrane, minimising the cleft with single cells without apparent detriment to viability. Excitation of such interfaces with light leads to effective cellular photostimulation. We find reversible light-induced conductance changes in ion-selective or temperature-gated channels.Nanomaterials that form a bioelectronic interface with cells are fascinating tools for controlling cellular behavior. Here, the authors photostimulate single cells with spiky assemblies of semiconducting quinacridone nanocrystals, whose nanoscale needles maximize electronic contact with the cells.
Research on semiconductor photocatalysts for the conversion of solar energy into chemical fuels has been at the forefront of renewable energy technologies. Water splitting to produce H2 and CO2 ...reduction to hydrocarbons are the two prominent approaches. A lesser‐known process, the conversion of solar energy into the versatile high‐energy product H2O2 via reduction of O2 has been proposed as an alternative concept. Semiconductor photoelectrodes for the direct photosynthesis of H2O2 from O2 have not been applied up to now. Photoelectrocatalytic oxygen reduction to peroxides in aqueous electrolytes by hydrogen‐bonded organic semiconductor is observed photoelectrodes. These materials have been found to be remarkably stable operating in a photoelectrochemical cell converting light into H2O2 under constant illumination for at least several days, functioning in a pH range from 1 to 12. This is the first report of a semiconductor photoelectrode for H2O2 production, with catalytic performance exceeding prior reports on photocatalysts by one to two orders of magnitude in terms of peroxide yield/catalyst amount/time. The combination of a strongly reducing conduction band energy level with stability in aqueous electrolytes opens new avenues for this widely available materials class in the field of photo(electro) catalysis.
Semiconductor photoelectrodes for reduction of O2 to H2O2 are reported for the first time, representing an alternative solar‐to‐chemical concept. This reaction is carried out by commercial organic pigments, widely available at low cost. The materials robustly photosynthesize peroxides, operating in a pH range from 1 to 12.
The optical properties and electrical conductivity of highly conducting poly(3,4-ethylenedioxythiophene) (PEDOT) doped with poly(styrenesulfonate) (PSS) are reported as a function of the processing ...additive conditions. The addition of dimethyl sulfoxide (DMSO) increases the conductivity and modifies the dielectric response as observed from the ellipsometric studies. Also the surface roughness and morphology change with the composition of PEDOT:PSS:DMSO and film deposition conditions. The real part of the dielectric function becomes negative in highly conducting samples, indicating the presence of delocalized charge carriers. The real and imaginary parts of the refractive index were determined as a function of wavelength. The results are consistent with the increase in conductivity upon the addition of DMSO.
•PEDOT:PSS was mixed with dimethyl sulfoxide.•The conductivity increase due to the coil extention is correlated with morphology.•Conductivity change correlates with morphology and extention of compact-coils.•The carrier delocalization is correlated with the dielectric function.
PDF
