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Low-bandgap near-infrared polymers are usually synthesized using the common donor-acceptor (D-A) approach. However, recently polymer chemists are introducing more complex chemical concepts for better fine tuning of their optoelectronic properties. Usually these studies are limited to one or two polymer examples in each case study so far, though. In this study, the dependence of optoelectronic and macroscopic (device performance) properties in a series of six new D-A 1 -D-A 2 low bandgap semiconducting polymers is reported for the first time. Correlation between the chemical structure of single-component polymer films and their optoelectronic properties has been achieved in terms of absorption maxima, optical bandgap, ionization potential, and electron affinity. Preliminary organic photovoltaic results based on blends of the D-A 1 -D-A 2 polymers as the electron donor mixed with the fullerene derivative [6,6]-phenyl-C 71 -butyric acid methyl ester demonstrate power conversion efficiencies close to 4% with short-circuit current densities (J sc ) of around 11 mA cm -2 , high fill factors up to 0.70, and high open-circuit voltages (V oc s) of 0.70 V. All the devices are fabricated in an inverted architecture with the photoactive layer processed in air with doctor blade technique, showing the compatibility with roll-to-roll large-scale manufacturing processes., (© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The synthesis of tetracene- and pentacene-annulated norbornadienes, formed through the Diels-Alder reaction of a dehydroacene with cyclopentadiene is reported. Ring-opening metathesis polymerization (ROMP) leads to polymers that are investigated with respect to their physical, optical, and electronic properties by gel permeation chromatography (GPC), UV-vis spectroscopy, and cyclic voltammetry. The pentacene-containing polymer P1 is successfully integrated into an organic field-effect transistor (OFET); the tetracene-containing polymer P2 is integrated into an organic light-emitting diode (OLED)., (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Due to their high transparency, electrodes fabricated from conductive polymers are often implemented in semitransparent organic solar cells. Opaque solar cells usually employ metal back electrodes with high reflectivity for best photon confinement in the light‐harvesting layer. Herein, a bilayer back electrode comprising conductive polymers and nanofoamed poly(methyl methacrylate) (PMMA) is investigated, the latter of which creates diffuse reflection of the incoming light. By tuning the thickness of the nanofoamed PMMA layer, absorption and transmission of the solar cells can be tailored from opaque to vastly transparent. Due to its diffusive character, this versatile electrode enhances the light absorption in the wavelength regimes with lower absorption coefficient. The solar cells are particularly suited for deployment in frosted window applications. [ABSTRACT FROM AUTHOR]

Abstract: Future low‐cost, high‐throughput production of organic solar cells in roll‐to‐roll printing processes calls for all‐solution‐processable device architectures. Mechanical flexibility and robustness are mandatory to roll the solar foils during printing and to eventually comply with certain end‐user requirements. Here, we report on semitransparent organic solar cells, comprising top and bottom silver nanowire (AgNW) electrodes that were embedded into conductive poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). The devices exhibited excellent robustness in bending experiments with radii of 5 and 2.5 mm as well as upon folding. To avoid short circuits from nanowires that could stick out of the bottom electrodes, the PEDOT:PSS:AgNW layers were flattened by hot‐pressing after deposition. All solar cells were fabricated in air by doctor blading and exhibited a clear (haze‐free) transparency due to the absence of bus bars. On photoactive areas of 0.5 cm2, power conversion efficiencies of 3.8 % were obtained. [ABSTRACT FROM AUTHOR]

ABSTRACT The systematic optimization of the chemical structure of low-bandgap (LBG) donor-acceptor polymeric semiconductors is a challenging task for which accurate guidelines are yet to be determined. Several different structural and molecular parameters are crucial ingredients for obtaining LBG polymers that simultaneously possess high power conversion efficiencies, good processability in common organic solvents, and enhanced stability in organic photovoltaic devices. In this work, we present an extensive structure-optoelectronic properties-solar cell performance study on the emerging class of diketopyrrolopyrrole-based LBG polymers. In particular, we investigate alkyl side chain positioning by introducing linear alkyl side chains into two different positions ( α- and β-), and the distance of the electron rich and electron deficient monomers within the repeat units of the polymer chain. We demonstrate that anchoring linear alkyl side chains to the α-positions and introducing fused moieties into the polymer backbone, can be beneficial toward maintaining photocurrents similar to the unsubstituted derivative, and concurrently exhibit better processabiliy in common organic solvents. These results can provide a design rationale towards further optimization of semiconducting polymers. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 138-146 [ABSTRACT FROM AUTHOR]

For future integration into building facades or overhead glazing, the direct deposition of organic solar modules on glass substrates in sheet-to-sheet processes may be more cost efficient than postproduction lamination. Complying with the special requirements for the deposition of the layer stack on glass substrates, we report on all-doctor-bladed organic solar modules yielding power conversion efficiencies of 4.5 and 3.6 % on photoactive areas of 1 and 20 cm2, respectively. The bottom electrode is doctor bladed from a silver ink atop an adhesion enhancing primer. The top electrode is applied from silver nanowires, dispersed in poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), which thereby avoids any visible bus bars and reduces shading of the active layer. Importantly, all layers are deposited under ambient conditions by using only non-chlorinated, eco-compatible solvents. [ABSTRACT FROM AUTHOR]

A fundamental analysis of the external quantum efficiency (EQE) of organic tandem solar cells with equal absorbers in both subcells (homo-tandem solar cells) is presented. Providing direct access to both subcells by introducing a conductive intermediate polymer electrode into the recombination zone, without changing the optical and electric device properties, the three-terminal device becomes a proxy to the two-terminal tandem solar cell properties. From the spectrally resolved EQE of the subcells in three-terminal configuration wavelength and intensity of suitable bias light as well as bias voltage are determined that in turn allow for accurate EQE measurements of the common two-terminal tandem solar cells. Theoretic considerations allow the prediction of the tandem solar cell's EQE from its subcells' EQEs as well as the prediction of the tandem cell EQE under monochromatic bias light illumination being in excellent agreement with experimental results. All findings discussed herein can be applied to more common hetero-tandem solar cell architectures likewise. [ABSTRACT FROM AUTHOR]

Abstract: Depositing a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) buffer layer or top-electrode from aqueous solution on a non-polar active layer in inverted organic solar cells is commonly considered a very challenging task. In this work we utilize spray deposited PEDOT:PSS seeds to effectively reduce the surface free energy atop the active layer in poly-hexylthiophene polymer solar cells before applying a PEDOT:PSS top-electrode. Though aqueous PEDOT:PSS is repelled from non-polar surfaces, very small droplets can adhere to the surface. The distribution of the sprayed PEDOT:PSS droplets can be controlled via the substrate temperature and the material flow rate. The less time the droplets have to contract along the surface before drying, the better is the surface seed coverage and the more homogenous is the formation of a subsequently deposited PEDOT:PSS electrode. The respective solar cells are semi-transparent and exhibit an overall power conversion efficiency η≈2%. [Copyright &y& Elsevier]

The thermoelectric performance of thin films fabricated from two commercially available, highly conductive polymer formulations based on poly (3,4-ethylendioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) was investigated. In order to enhance the electrical conductivity, the high-boiling solvent dimethyl sulfoxide (DMSO) was added. By changing the content of DMSO the electrical conductivity was increased by a factor of two without changing the Seebeck coefficient or the thermal conductivity. We achieved ZT = 9.2 × 10 at room temperature upon the addition of 5 vol.% DMSO to the PEDOT:PSS formulation. [ABSTRACT FROM AUTHOR]

The design of solution processable multi-layer organic light emitting diodes (OLEDs) is often hampered by the choice of solvents. To avoid the dissolution of the emission layer upon the subsequent deposition of further functional layers, we synthesize and investigate thermo-cleavage in poly[2,7-(3-(9-methyl-9H-fluorene-9-yl)propyl (2-methylhexane-2-yl) carbonate)-alt-4,7-(benzo[c][1,2,5]thiadiazole)] (c-F8BT). Employed in OLEDs, the non-cleaved polymer yields about the same current efficiency as state-of-the-art F8BT. During pyrolysis at 200 °C, the polymer releases its solubility groups, fully maintaining the device efficiency but becoming insoluble. This feature allows to enhance the OLED performance by applying an additional bathophenanthroline hole blocking layer from solution or by incorporating a low-molecular weight electron transport moiety into the affixing polymer matrix. [ABSTRACT FROM AUTHOR]

Highlights: [•] Suppressing molecular aggregation in small-molecule OLEDs. [•] Solution processing of small-molecule layers. [•] Influence of electrical isolating polymers on the OLED performance. [•] STEM-HAADF investigations of small-molecule layers. [ABSTRACT FROM AUTHOR]

Abstract: We present a transparent, fully solution-processed top anode system comprising a thin, conductive polymer interlayer below a silver nanowire mesh for efficient organic electronic devices. We fabricate inverted semi-transparent polymer solar cells exhibiting power conversion efficiencies that are comparable to devices incorporating an opaque electrode. By means of scanning electron microscopy and light beam induced photocurrent measurements we show that the thin polymer interlayer facilitates charge extraction from the active layer and efficient transport to the metallic nanowire mesh. [Copyright &y& Elsevier]

The drying process of the bulk heterojunction (BHJ) layerhas a strong impact on the solar cell performance for the well-investigatedmaterial system P3HT:PC61BM. For higher performing low-bandgappolymers and C71fullerene derivatives, no comprehensivestudies of the BHJ structure evolution during film drying are available.In this work we investigate the structure formation of the low-bandgappolymer poly{[4,40-bis(2-ethylhexyl)dithieno(3,2-b;20,30-d)silole]-2,6-diyl-alt-(2,1,3-benzothidiazole)-4,7-diyl}(PSBTBT) and [6,6]-phenyl C71-butyric acid methyl ester(PC71BM) in the transition from wet to solid by in-situgrazing incidence X-ray diffraction (GIXD) and laser reflectometrysimultaneously. The nucleation and crystallization of PSBTBT differsfrom the interface-induced crystallization of P3HT and occurs partiallyin the solution. It is shown that PSBTBT:PC71BM blend nanomorphologyand optoelectronic device properties are rather insensitive to thedrying process in the investigated temperature range of 40–85°C. This is beneficial for fast drying at elevated temperatureswhich enables high throughput fabrication of efficient organic photovoltaics. [ABSTRACT FROM AUTHOR]

Abstract: The rapidly increasing power conversion efficiencies of organic solar cells are an important prerequisite towards low cost photovoltaic fabricated in high throughput. In this work we suggest indane as a non-halogenated replacement for the commonly used halogenated solvent o-dichlorobenzene. Indane was blended with the higher volatile solvents chloroform or toluene or o-xylene in order to improve wettability and to reduce drying time. The combination of high volatile solvents with the less volatile host solvent indane allows for an increased fabrication speed due to a reduction of the overall drying time and provides films with good light absorption behavior and high polymer crystallinity. For the solvent mixture toluene–indane, solar cell performance is comparable to the o-dichlorobenzene reference device indicating this mixture as a suitable replacement for increased productivity without drawbacks in nanomorphology as investigated by atomic force microscopy (AFM) and grazing incidence X-ray diffraction (GIXD). This study provides a fundamental understanding on solvent mixture drying kinetics and can aid the ink formulation. [Copyright &y& Elsevier]