Impact of polymorphism on the optoelectronic properties of a low-bandgap semiconducting polymer.

Polymorphism of organic semiconducting materials exerts critical effects on their physical properties such as optical absorption, emission and electrical conductivity, and provides an excellent platform for investigating structure-property relations. It is, however, challenging to efficiently tune the polymorphism of conjugated polymers in aggregated, semi-crystalline phases due to their conformational freedom and anisotropic nature. Here, two distinctly different semi-crystalline polymorphs (β and β) of a low-bandgap diketopyrrolopyrrole polymer are formed through controlling the solvent quality, as evidenced by spectroscopic, structural, thermal and charge transport studies.

Diffusion-Limited Crystallization: A Rationale for the Thermal Stability of Non-Fullerene Solar Cells.

Organic solar cells are thought to suffer from poor thermal stability of the active layer nanostructure, a common belief that is based on the extensive work that has been carried out on fullerene-based systems. We show that a widely studied non-fullerene acceptor, the indacenodithienothiophene-based acceptor ITIC, crystallizes in a profoundly different way as compared to fullerenes. Although fullerenes are frozen below the glass-transition temperature T of the photovoltaic blend, ITIC can undergo a glass-crystal transition considerably below its high T of ∼180 °C.

On the homocoupling of trialkylstannyl monomers in the synthesis of diketopyrrolopyrrole polymers and its effect on the performance of polymer-fullerene photovoltaic cells.

Homocoupling of monomers in a palladium-catalyzed copolymerization of donor-acceptor polymers affects the perfect alternating structure and may deteriorate the performance of such materials in solar cells. Here we investigate the effect of homocoupling bis(trialkylstannyl)-thiophene and -bithiophene monomers in two low band gap poly(diketopyrrolopyrrole--oligothiophene) polymers by deliberately introducing extended oligothiophene defects in a controlled fashion. We find that extension of the oligothiophene by one or two thiophenes and creating defects up to at least 10% does not significantly affect the opto-electronic properties of the polymers or their photovoltaic performance as electron donor in solar cells in combination with [6,6]-phenyl C butytic acid methyl ester as acceptor.

Effect of Branching on the Optical Properties of Poly(-phenylene ethynylene) Conjugated Polymer Nanoparticles for Bioimaging.

Fluorescent conjugated polymers formulated in nanoparticles show attractive properties to be used as bioimaging probes. However, their fluorescence brightness is generally limited by quenching phenomena due to interchain aggregation in the confined nanoparticle space. In this work, branched conjugated polymer networks are investigated as a way to enhance the photoluminescence quantum yield of the resulting conjugated polymer nanoparticles (CPNs).

Emissive and charge-generating donor-acceptor interfaces for organic optoelectronics with low voltage losses.

Intermolecular charge-transfer states at the interface between electron donating (D) and accepting (A) materials are crucial for the operation of organic solar cells but can also be exploited for organic light-emitting diodes. Non-radiative charge-transfer state decay is dominant in state-of-the-art D-A-based organic solar cells and is responsible for large voltage losses and relatively low power-conversion efficiencies as well as electroluminescence external quantum yields in the 0.01-0.

The influence of siloxane side-chains on the photovoltaic performance of a conjugated polymer.

The effect of gradually replacing the branched alkyl side chains of a diketopyrrolopyrrole (DPP) conjugated polymer by linear side chains containing branched siloxane end groups on the photovoltaic performance of blends of these polymers with a common fullerene acceptor is investigated. With an increasing proportion of siloxane side chains, the molecular weight and solubility of the polymers decreases. While the siloxane containing polymers exhibit a higher hole mobility in field-effect transistors, their performance in solar cells is less than the polymer with only alkyl sides chains.

Degradation pathways in standard and inverted DBP-C based organic solar cells.

Achieving long-term stability in organic solar cells is a remaining bottleneck for the commercialization of this otherwise highly appealing technology. In this work, we study the performance and stability differences in standard and inverted DBP/C based organic solar cells. Differences in the charge-transfer state properties of inverted and standard configuration DBP/C solar cells are revealed by sensitive external quantum efficiency measurements, leading to differences in the open-circuit voltages of the devices.

Towards 2D layered hybrid perovskites with enhanced functionality: introducing charge-transfer complexes via self-assembly.

This study broadens the family of 2D layered perovskites by demonstrating that it is possible to self-assemble organic charge-transfer complexes in their organic layer. Organic charge-transfer complexes, formed by combining charge-donating and charge-accepting molecules, are a diverse class of materials that can possess exceptional optical and electronic properties.

Energy-Gap Law for Photocurrent Generation in Fullerene-Based Organic Solar Cells: The Case of Low-Donor-Content Blends.

The involvement of charge-transfer (CT) states in the photogeneration and recombination of charge carriers has been an important focus of study within the organic photovoltaic community. In this work, we investigate the molecular factors determining the mechanism of photocurrent generation in low-donor-content organic solar cells, where the active layer is composed of vacuum-deposited C and small amounts of organic donor molecules. We find a pronounced decline of all photovoltaic parameters with decreasing CT state energy.

Understanding the Importance of Cu(I) Intermediates in Self-Reducing Molecular Inks for Flexible Electronics.

Fast and scalable low-temperature deposition of microscale metallic features is of utmost importance for the development of future flexible smart applications including sensors, wireless communication, and wearables. Recently, a new class of metal-organic decomposition (MOD) copper inks was developed, consisting of self-reducing copper formate containing amine complexes. From these novel inks, copper metal features with outstanding electrical conductivity (±10 S cm) are deposited at a temperature of 150 °C or less, which is well below the reduction temperature of orthorhombic α-copper formate (around 225 °C).

Surface Chemistry of Oil-Filled Organic Nanoparticle Coated Papers Analyzed Using Micro-Raman Mapping.

Raman spectroscopy and micro-Raman mapping have been used to study the distribution of different chemical components at the surface of coated papers. The paper coatings contain organic nanoparticles with a structure of poly(styrene- co-maleimide) and encapsulated vegetable oils. Raman spectroscopy is able to differentiate between various types of oil, i.

The Impact of Acceptor-Acceptor Homocoupling on the Optoelectronic Properties and Photovoltaic Performance of PDTSQx Low Bandgap Polymers.

Push-pull-type conjugated polymers applied in organic electronics do not always contain a perfect alternation of donor and acceptor building blocks. Misscouplings can occur, which have a noticeable effect on the device performance. In this work, the influence of homocoupling on the optoelectronic properties and photovoltaic performance of PDTSQx polymers is investigated, with a specific focus on the quinoxaline acceptor moieties.

Links Between Heathland Fungal Biomass Mineralization, Melanization, and Hydrophobicity.

Comprehending the decomposition process is crucial for our understanding of the mechanisms of carbon (C) sequestration in soils. The decomposition of plant biomass has been extensively studied. It revealed that extrinsic biomass properties that restrict its access to decomposers influence decomposition more than intrinsic ones that are only related to its chemical structure.

Printing Smart Designs of Light Emitting Devices with Maintained Textile Properties.

To maintain typical textile properties, smart designs of light emitting devices are printed directly onto textile substrates. A first approach shows improved designs for alternating current powder electroluminescence (ACPEL) devices. A configuration with the following build-up, starting from the textile substrate, was applied using the screen printing technique: silver (10 µm)/barium titanate (10 µm)/zinc-oxide (10 µm) and poly(3,4-ethylenedioxythiophene)poly(styrenesulfonate) (10 µm).

Ti surface doping of LiNiMnO positive electrodes for lithium ion batteries.

The particle surface of LiNiMnO (LNMO), a Li-ion battery cathode material, has been modified by Ti cation doping through a hydrolysis-condensation reaction followed by annealing in oxygen. The effect of different annealing temperatures (500-850 °C) on the Ti distribution and electrochemical performance of the surface modified LNMO was investigated. Ti cations diffuse from the preformed amorphous 'TiO ' layer into the LNMO surface during annealing at 500 °C.

The effect of side-chain substitution and hot processing on diketopyrrolopyrrole-based polymers for organic solar cells.

The effects of cold and hot processing on the performance of polymer-fullerene solar cells are investigated for diketopyrrolopyrrole (DPP) based polymers that were specifically designed and synthesized to exhibit a strong temperature-dependent aggregation in solution. The polymers, consisting of alternating DPP and oligothiophene units, are substituted with linear and second position branched alkyl side chains. For the polymer-fullerene blends that can be processed at room temperature, hot processing does not enhance the power conversion efficiencies compared to cold processing because the increased solubility at elevated temperatures results in the formation of wider polymer fibres that reduce charge generation.

Conjugated Polymer Nanoparticles for Bioimaging.

During the last decade, conjugated polymers have emerged as an interesting class of fluorescence imaging probes since they generally show high fluorescence brightness, high photostability, fast emission rates, non-blinking behavior and low cytotoxicity. The main concern related to most conjugated polymers is their lack of hydrophilicity and thereby poor bio-availability. This can, however, be overcome by the formulation of conjugated polymer nanoparticles in aqueous medium.

Absorption and Fluorescence Features of an Amphiphilic meso-Pyrimidinylcorrole: Experimental Study and Quantum Chemical Calculations.

Corroles are emerging as an important class of macrocycles with numerous applications because of their peculiar photophysical and metal chelating properties. meso-Pyrimidinylcorroles are easily deprotonated in certain solvents, which changes their absorption and emission spectra as well as their accessible supramolecular structures. To enable control over the formation of supramolecular structures, the dominant corrole species, i.

Remarkable lowering in the synthesis temperature of LiMnOvia citrate solution-gel synthesis facilitated by ethanol.

LiMnO (LMO) is interesting from the viewpoint of its energy storage applications as it is a cathode in lithium ion batteries (LIB), which contains no rare, toxic or expansive elements, while it provides a high theoretical capacity (148 mA h g) at a reasonable voltage (4 V region) and a higher thermal stability compared to cobalt based cathodes and has a good rechargeability and cycling stability due to its spinel structure. Low temperature synthesis routes for cathode materials are currently gaining attention, in order to decrease the ecological footprint of the final LIB. Here, the crystallization temperature of LMO by a citrate based solution-gel synthesis was significantly lowered, to as low as 250 °C by the addition of ethanol to the precursor.

A novel explanation for the increased conductivity in annealed Al-doped ZnO: an insight into migration of aluminum and displacement of zinc.

A combined experimental and first-principles study is performed to study the origin of conductivity in ZnO:Al nanoparticles synthesized under controlled conditions via a reflux route using benzylamine as a solvent. The experimental characterization of the samples by Raman, nuclear magnetic resonance (NMR) and conductivity measurements indicates that upon annealing in nitrogen, the Al atoms at interstitial positions migrate to the substitutional positions, creating at the same time Zn interstitials. We provide evidence for the fact that the formed complex of Al and Zn corresponds to the origin of the Knight shifted peak (KS) we observe in Al NMR.

Steering the Properties of MoOx Hole Transporting Layers in OPVs and OLEDs: Interface Morphology vs. Electronic Structure.

The identification, fine-tuning, and process optimization of appropriate hole transporting layers (HTLs) for organic solar cells is indispensable for the production of efficient and sustainable functional devices. In this study, the optimization of a solution-processed molybdenum oxide (MoOx) layer fabricated from a combustion precursor is carried out via the introduction of zirconium and tin additives. The evaluation of the output characteristics of both organic photovoltaic (OPV) and organic light emitting diode (OLED) devices demonstrates the beneficial influence upon the addition of the Zr and Sn ions compared to the generic MoOx precursor.

Versatile Approach for the Synthesis of Sequence-Defined Monodisperse 18- and 20-mer Oligoacrylates.

Linear monodisperse 18- and 20-mer acrylates are obtained via consecutive synthesis of two sequence-defined acrylate 9- and 10-mers, followed by disulfide coupling utilizing reversible addition-fragmentation chain transfer (RAFT) end group chemistry. The sequence-defined oligoacrylates are accessed via consecutive single (SUMI) and multiple (MUMI) unit monomer insertions through RAFT polymerization, using the extensive acrylate monomer library as functional building blocks. Aminolysis of the trithiocarbonate macroRAFT end group and in situ oxidation of the thiols to form a disulfide bridge lead to the formation of 18- and 20-mer acrylates.

Tuning the optical properties of poly(p-phenylene ethynylene) nanoparticles as bio-imaging probes by side chain functionalization.

Conjugated polymers are versatile bio-imaging probes as their optical properties can be readily fine-tuned. In this manuscript, fluorescent conjugated polymer nanoparticles are fabricated using three different poly(p-phenylene ethynylene) (PPE) derivatives. The polymers have the same backbone but carry different side chains, i.

Ultrasonically spray coated silver layers from designed precursor inks for flexible electronics.

Integration of electronic circuit components onto flexible materials such as plastic foils, paper and textiles is a key challenge for the development of future smart applications. Therefore, conductive metal features need to be deposited on temperature sensitive substrates in a fast and straightforward way. The feasibility of these emerging (nano-) electronic technologies depends on the availability of well-designed deposition techniques and on novel functional metal inks.

Absorption Tails of Donor:C Blends Provide Insight into Thermally Activated Charge-Transfer Processes and Polaron Relaxation.

In disordered organic semiconductors, the transfer of a rather localized charge carrier from one site to another triggers a deformation of the molecular structure quantified by the intramolecular relaxation energy. A similar structural relaxation occurs upon population of intermolecular charge-transfer (CT) states formed at organic electron donor (D)-acceptor (A) interfaces. Weak CT absorption bands for D-A complexes occur at photon energies below the optical gaps of both the donors and the C acceptor as a result of optical transitions from the neutral ground state to the ionic CT state.