Dielectric constant engineering of organic semiconductors: effect of planarity and conjugation length

Bulk heterojunction organic solar cells continue to show steady photoconversion efficiency improvements. However, single component organic solar cells are a particularly attractive alternative due to the relative simplicity of device manufacture. It has been proposed that organic semiconductors with a high dielectric constant (≈10) could give rise to spontaneous free charge carrier generation upon photoexcitation. In this manuscript, factors are explored that affect the dielectric constant of organic semiconductors, particularly the optical-frequency dielectric constant. The properties of monomers, dimers and trimers of two isoelectronic families of materials that have acceptor units composed of one or two dicyanovinylbenzothiadiazole moieties and one to three donor units are compared. The donor components are composed of either fluorenyl or cyclopentadithiophene moieties with the same glycol-based solubilizing groups. It is found that chromophore planarity and orientation with respect to the substrate, and film density affect the optical and electronic properties of the materials, especially the high-frequency dielectric constant. The results also indicate that delocalization of the highest occupied and lowest unoccupied molecular orbitals is a critical factor. The dimer with two dicyanovinylbenzothiadiazole moieties and two dithienocyclopentadiene units is found to have the highest optical frequency dielectric constant and overall performance

Dielectric constant engineering of organic semiconductors: effect of planarity and conjugation length

Bulk heterojunction organic solar cells continue to show steady photoconversion efficiency improvements. However, single component organic solar cells are a particularly attractive alternative due to the relative simplicity of device manufacture. It has been proposed that organic semiconductors with a high dielectric constant (≈10) could give rise to spontaneous free charge carrier generation upon photoexcitation. In this manuscript, factors are explored that affect the dielectric constant of organic semiconductors, particularly the optical-frequency dielectric constant. The properties of monomers, dimers and trimers of two isoelectronic families of materials that have acceptor units composed of one or two dicyanovinylbenzothiadiazole moieties and one to three donor units are compared. The donor components are composed of either fluorenyl or cyclopentadithiophene moieties with the same glycol-based solubilizing groups. It is found that chromophore planarity and orientation with respect to the substrate, and film density affect the optical and electronic properties of the materials, especially the high-frequency dielectric constant. The results also indicate that delocalization of the highest occupied and lowest unoccupied molecular orbitals is a critical factor. The dimer with two dicyanovinylbenzothiadiazole moieties and two dithienocyclopentadiene units is found to have the highest optical frequency dielectric constant and overall performance

In Memoriam: A Memoir for Our Fallen "Heroes"

This article is made available for unrestricted research re-use and secondary analysis in any form or be any means with acknowledgement of the original source. These permissions are granted for the duration of the World Health Organization (WHO) declaration of COVID-19 as a global pandemic.Even though neurosurgeons exercise these enormous and versatile skills, the COVID-19 pandemic has shaken the fabrics of the global neurosurgical family, jeopardizing human lives, and forcing the entire world to be locked down. We stand on the shoulders of the giants and will not forget their examples and their teachings. We will work to the best of our ability to honor their memory. Professor Harvey Cushing said: “When to take great risks; when to withdraw in the face of unexpected difficulties; whether to force an attempted enucleation of a pathologically favorable tumor to its completion with the prospect of an operative fatality, or to abandon the procedure short of completeness with the certainty that after months or years even greater risks may have to be faced at a subsequent session—all these require surgical judgment which is a matter of long experience.” It is up to us, therefore, to keep on the noble path that we have decided to undertake, to accumulate the surgical experience that these icons have shown us, the fruit of sacrifice and obstinacy. Our tribute goes to them; we will always remember their excellent work and their brilliant careers that will continue to enlighten all of us. This memorial is intended to commemorate our colleagues who succumbed during the first 4 months

Combining computational and experimental approaches to select chromophores to enable the detection of fatty acids: Via HPLC

This paper outlines a protocol, which combines quantum mechanics calculations and experimental synthesis, to enable systematic selection of suitable chromophores based on their stability of fluorescence and efficiency of the chemical reaction. The experimental conditions were optimised for the esterification of fatty acids with the most effective chromophore, 5-(4-(diphenylamine)phenylthiopheny-2-yl)methanol

A non-fullerene electron acceptor based on central carbazole and terminal diketopyrrolopyrrole functionalities for efficient, reproducible and solution-processable bulk-heterojunction devices

A novel, solution-processable non-fullerene electron acceptor, 6,6′-((9-(heptadecan-9-yl)-9H-carbazole-2,7-diyl)bis(thiophene-5,2-diyl))bis(2,5-bis(2-ethylhexyl)-3-(thiophen-2-yl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione) (coded as N7), based on central carbazole and terminal diketopyrrolopyrrole building blocks was designed, synthesized and characterized. N7 displayed excellent solubility, thanks to its design allowing incorporation of numerous lipophilic chains, thermal stability, and afforded a 2.30% power conversion efficiency with a high open-circuit voltage (1.17 V) when tested with the conventional donor polymer poly(3-hexylthiophene) in solution-processable bulk-heterojunction devices. To our knowledge, not only is N7 the first reported chromophore based on carbazole and diketopyrrolopyrrole functionalities but the open-circuit voltage reported here is among the highest values for a single junction bulk-heterojunction device that has been fabricated using a simple device architecture, with reproducible outcomes and with no special treatment

Application of an A-A'-A-Containing acceptor polymer in sequentially deposited all-polymer solar cells

PNNT has been prepared as a polymeric electron acceptor for organic solar cells. The polymer has an A-A'-A acceptor motif linked alternatively with thiophene and vinyl moieties. The A'-unit is a naphthalene diimide, while the A groups are thiazoles. PNNT films were found to have an estimated electron affinity of ≈4.3 eV and an electron mobility of the order of 10 cm V s. Its relatively low solubility in common chlorinated solvents at ambient temperature allowed the manufacture of sequentially deposited (SD) devices, which were found to have significantly higher efficiency than that of bulk heterojunction (BHJ) solar cells containing the same materials. Grazing-incidence wide-angle X-ray scattering measurements indicated that the SD films retained the ordering of the individual polymers to a greater extent compared to the BHJ films. The best SD devices were found to have a power conversion efficiency of up to 4.5%, with stable performance under thermal stress

Effect of capping group on the properties of non-polymeric diketopyrrolopyrroles for solution-processed bulk heterojunction solar cells

Solution-processable non-polymeric organic semiconductors are attractive for opto-electronic applications due to their relatively simple synthetic reproducibility and characterization, and enhanced capability for fine-tuning of their properties. We report the synthesis, charge transport, photophysics, and photovoltaic properties of three non-polymeric materials based upon bisarylthiophenyl diketopyrrolopyrrole [DPP(ThAr)(2)]. The DPP(ThAr)(2) molecules are comprised of solubilizing alkyl groups, 2-ethylhexyl (for 1a) and 2-octyldodecyl (for 1b and 2), which are capped with "electron accepting" moieties -fluorenone (1) or benzothiadiazole (2). While the materials could be prepared under standard SuzukiMiyaura cross-coupling conditions, a simple direct arylation afforded 2 and 1b in good yields. We found 1a with a short alkyl chain lacked sufficient solubility for solution processing but 1b and 2 are solution processable and form good quality films. All three materials exhibited ambipolar charge transport in field effect transistors, with 1b showing balanced charge mobilities of about 10(-3) cm(2) V-1 s(-1). Bulk heterojunction solar cells of 1b or 2 with PC71BM were found to have high opencircuit voltages (up to 0.9 V) with power conversion efficiencies of up to 4.5% and 2.6%, respectively. (C) 2017 Elsevier B.V. All rights reserved