Inverse Optical Cavity Design for Ultrabroadband Light Absorption Beyond the Conventional Limit in Low-Bandgap Nonfullerene Acceptor–Based Solar Cells

In the subwavelength regime, several nanophotonic configurations have been proposed to overcome the conventional light trapping or light absorption enhancement limit in solar cells also known as the Yablonovitch limit. It has been recently suggested that establishing such limit should rely on computational inverse electromagnetic design instead of the traditional approach combining intuition and a priori known physical effect. In the present work, by applying an inverse full wave vector electromagnetic computational approach, a 1D nanostructured optical cavity with a new resonance configuration is designed that provides an ultrabroadband (˜450 nm) light absorption enhancement when applied to a 107 nm thick active layer organic solar cell based on a low-bandgap (1.32 eV) nonfullerene acceptor. It is demonstrated computationally and experimentally that the absorption enhancement provided by such a cavity surpasses the conventional limit resulting from an ergodic optical geometry by a 7% average over a 450 nm band and by more than 20% in the NIR. In such a cavity configuration the solar cells exhibit a maximum power conversion efficiency above 14%, corresponding to the highest ever measured for devices based on the specific nonfullerene acceptor used.Peer ReviewedPostprint (author's final draft

Mononuclear lanthanide(III)-salicylideneaniline complexes: synthetic, structural, spectroscopic and magnetic studies

The reactions of hydrated lanthanide(III) [Ln(III)] nitrates and salicylideneaniline (salanH) have provided access to two families of mononuclear complexes depending on the reaction solvent used. In MeCN, the products are [Ln(NO3)3(salanH)2(H2O)]·MeCN, and, in MeOH, the products are [Ln(NO3)3(salanH)2(MeOH)]·(salanH). The complexes within each family are proven to be isomorphous. The structures of complexes [Ln(NO3)3(salanH)2(H2O)]·MeCN (Ln = Eu, 4·MeCN_Eu, Ln = Dy, 7·MeCN_Dy; Ln = Yb, 10·MeCN_Yb) and [Ln(NO3)3(salanH)2(MeOH)]·(salanH) (Ln = Tb, 17_Tb; Ln = Dy, 18_Dy) have been solved by single-crystal X-ray crystallography. In the five complexes, the LnIII center is bound to six oxygen atoms from the three bidentate chelating nitrato groups, two oxygen atoms from the two monodentate zwitterionic salanH ligands, and one oxygen atom from the coordinated H2O or MeOH group. The salanH ligands are mutually "cis" in 4·MeCN_Eu, 7·MeCN_Dy and 10·MeCN_Yb while they are "trans" in 17_Tb and 18_Dy. The lattice salanH molecule in 17_Tb and 18_Dy is also in its zwitterionic form with the acidic H atom being clearly located on the imine nitrogen atom. The coordination polyhedra defined by the nine oxygen donor atoms can be described as spherical tricapped trigonal prisms in 4·MeCN_Eu, 7·MeCN_Dy, and 10·MeCN_Yb and as spherical capped square antiprisms in 17_Tb and 18_Dy. Various intermolecular interactions build the crystal structures, which are completely different in the members of the two families. Solid-state IR data of the complexes are discussed in terms of their structural features. 1H NMR data for the diamagnetic Y(III) complexes provide strong evidence that the compounds decompose in DMSO by releasing the coordinated salanH ligands. The solid complexes emit green light upon excitation at 360 nm (room temperature) or 405 nm (room temperature). The emission is ligand-based. The solid Pr(III), Nd(III), Sm(III), Er(III), and Yb(III) complexes of both families exhibit LnIII-centered emission in the near-IR region of the electromagnetic spectrum, but there is probably no efficient salanH→LnIII energy transfer responsible for this emission. Detailed magnetic studies reveal that complexes 7·MeCN_Dy, 17_Tb and 18_Dy show field-induced slow magnetic relaxation while complex [Tb(NO3)3(salanH)2(H2O)]·MeCN (6·MeCN_Tb) does not display such properties. The values of the effective energy barrier for magnetization reversal are 13.1 cm−1 for 7·MeCN_Dy, 14.8 cm−1 for 17_Tb, and 31.0 cm−1 for 18_Dy. The enhanced/improved properties of 17_Tb and 18_Dy, compared to those of 6_Tb and 7_Dy, have been correlated with the different supramolecular structural features of the two families. The molecules [Ln(NO3)3(salanH)2(MeOH)] of complexes 17_Tb and 18_Dy are by far better isolated (allowing for better slow magnetic relaxation properties) than the molecules [Ln(NO3)3(salanH)2(H2O)] in 6·MeCN_Tb and 7·MeCN_Dy. The perspectives of the present initial studies in the Ln(III)/salanH chemistry are discussed

Polymorphism in Non-Fullerene Acceptors Based on Indacenodithienothiophene

Financiado para publicación en acceso aberto: Universidade da Coruña/CISUG[Abstract] Organic solar cells incorporating non-fullerene acceptors (NFAs) have reached remarkable power conversion efficiencies of over 18%. Unlike fullerene derivatives, NFAs tend to crystallize from solutions, resulting in bulk heterojunctions that include a crystalline acceptor phase. This must be considered in any morphology-function models. Here, it is confirmed that high-performing solution-processed indacenodithienothiophene-based NFAs, i.e., ITIC and its derivatives ITIC-M, ITIC-2F, and ITIC-Th, exhibit at least two crystalline forms. In addition to highly ordered polymorphs that form at high temperatures, NFAs arrange into a low-temperature metastable phase that is readily promoted via solution processing and leads to the highest device efficiencies. Intriguingly, the low-temperature forms seem to feature a continuous network that favors charge transport despite of a poorly order along the π–π stacking direction. As the optical absorption of the structurally more disordered low-temperature phase can surpass that of the more ordered polymorphs while displaying comparable—or even higher—charge transport properties, it is argued that such a packing structure is an important feature for reaching highest device efficiencies, thus, providing guidelines for future materials design and crystal engineering activities.This work was supported by the Ministerio de Ciencia e Innovacion/FEDER (under Ref. PGC2018-094620-A-I00 and PGC2018-095411-B-I00, CEX2019-000917-S, and PGC2018-095411-B-100) and the Basque Country Government (Ref. PIBA19-0051). S.M. is grateful to POLYMAT for the doctoral scholarship. The authors thank A. Arbe, A. Alonso-Mateo, and L. Hueso for their support and access to characterization tools. The authors also thank the technical and human support provided by SGIker of UPV/EHU and European funding (ERDF and ESF). GIWAXS experiments were performed at BL11 NCD-SWEET beamline at ALBA Synchrotron (Spain) with the collaboration of ALBA staff. J.M and E.F.-G. acknowledge support through the European Union's Horizon 2020 research and innovation program, H2020-FETOPEN 01-2018-2020 (FET-Open Challenging Current Thinking), “LION-HEARTED,” Grant Agreement No. 828984. J.M and N.S. would like to thank the financial support provided by the IONBIKE RISE project, which received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie Grant Agreement No. 823989. N.S., A.K., and A.B. furthermore are grateful to the U.S. National Science Foundation (NSF) for support via Project No. 1905901 within NSF's Division of Materials Research. A.S. and M.C. acknowledge financial support by the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program “HEROIC,” Grant Agreement No. 638059. This work was partially carried out at Polifab, the micro- and nanotechnology center of the Politecnico di Milano. C.M. thanks the Knut and Alice Wallenberg Foundation for funding through the project “Mastering Morphology for Solution-borne Electronics.” A.I. thanks MICINN for a Personal Técnico de Apoyo contract (PTA2017-14359-I) and gratefully acknowledge the financial support of the Basque Government (Research Groups IT-1175-19) and the MICINN (PGC2018-094548-B-I00, MCIU/AEI/FEDER, UE. Funding for open access charge: Universidade da Coruña/CISUG.Gobierno Vasco; PIBA19-0051Gobierno Vasco; IT-1175-19Estados Unidos. National Science Foundation; 190590

Echinoderms from the Museum of Zoology from the Universidad de Costa Rica

El Museo de Zoología de la Universidad de Costa Rica (MZUCR) se funda en 1966 y alberga la colección de organismos vertebrados e invertebrados más completa de Costa Rica. El MZUCR cuenta actualmente con 24 colec-ciones que contienen más de cinco millones de especíme-nes, y más de 13 000 especies identificadas. Las primeras colecciones datan 1960 e incluyen peces, reptiles, anfibios, poliquetos, crustáceos y equinodermos. Para este último grupo, el MZUCR posee un total de 157 especies, en 1 173 lotes y 4 316 ejemplares. Estas 157 especies representan el 54% del total de especies de equinodermos que posee Costa Rica (293 especies). El resto de especies están repar-tidas en las siguientes instituciones: Academia de la Cien-cias de California (CAS) (4.8%), Instituto Oceanográfico Scripps (SIO) (5.2%), en la Colección Nacional de equino-dermos “Dra. Ma. Elena Caso” de la Universidad Nacional Autónoma de México (ICML-UNAM) (12.7%), Museo de Zoología Comparada de Harvard (MZC) (19.2%), y en el Museo Nacional de Historia Natural del Instituto Smithso-niano (USNM) (35.1%). Es posible que haya material de Costa Rica en el Museo de Historia Natural de Dinamarca (NCD) y en el Museo de Historia Natural de los Ángeles (LACM), sin embargo, no hubo acceso a dichas coleccio-nes. A su vez hay 9.6% de especies que no aparecen en ningún museo, pero están reportadas en la literatura. Con base en esta revisión de colecciones se actualizó el listado taxonómico de equinodermos para Costa Rica que consta de 293 especies, 152 géneros, 75 familias, 30 órdenes y cinco clases. La costa Pacífica de Costa Rica posee 153 especies, seguida por la isla del Coco con 134 y la costa Caribe con 65. Holothuria resultó ser el género más rico con 25 especies.The Museum of Zoology, Universidad de Costa Rica (MZUCR) was founded in 1966 and houses the most complete collection of vertebrates and invertebrates in Costa Rica. The MZUCR currently has 24 collections containing more than five million specimens, and more than 13 000 species. The earliest collections date back to 1960 and include fishes, reptiles, amphibians, polychaetes, crustaceans and echinoderms. For the latter group, the MZUCR has a total of 157 species, in 1 173 lots and 4 316 specimens. These 157 species represent 54% of the total species of echino-derms from Costa Rica. The remaining species are distributed in the following institutions: California Academy of Sciences (CAS) (4.8%), Scripps Oceanographic Institute (SIO) (5.2%), National Echinoderm Collection “Dr. Ma. Elena Caso” from the National Autonomous University of Mexico (ICML-UNAM) (12.7%), the National Museum of Natural History, Smithsonian Institute (USNM) (35.1%), and the Harvard Museum of Comparative Zoology (19.2%). There may be material from Costa Rica in the Natural History Museum of Denmark (NCD) and the Natural History Museum of Los Angeles (LACM), however, there was no access to such collections. There are 9.6% that do not appear in museums, but are reported in the literature. Based on this revision, the taxonomic list of echinoderms for Costa Rica is updated to 293 species, 152 genera, 75 families, 30 orders and 5 classes. The Pacific coast of Costa Rica has 153 species, followed by the Isla del Coco with 134 and the Caribbean coast with 65. Holothuria is the most diverse genus with 25 species.UCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de BiologíaUCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Básicas::Centro de Investigación en Ciencias del Mar y Limnología (CIMAR)UCR::Vicerrectoría de Investigación::Unidades de Investigación::Artes y Letras::Museo de la Universidad de Costa Ric

Investigating Thermoelectric Stability under Encapsulation Using PEI-Doped CNT Films as a Model System

The stability of organic semiconductors is an important topic, which in the case of organic thermoelectrics (OTEs), has not yet got the attention it deserves. This work presents a simple method which allows to characterize the stability of OTEs, using patterned ITO substrates to electrically contact encapsulated samples. The method is applied to n‐doped carbon nanotube films, a well‐suited reference system due to their sensitivity to changes in doping level, and used to compare the effectiveness of different encapsulation methods. In the observed films, oxygen adsorption leads to a gradual p‐doping. Among the investigated barrier materials, glass performs best. Flexible alternatives like transferred films of barrier polymers also show promise, while barrier films deposited by dropcast performed worse, likely due to their inhomogeneity. Finally, Raman imaging is shown to be a useful technique to investigate degradation in OTEs.The authors would like to thank Aleksandr Perevedentsev for advice with the EVOH film transfer. The authors acknowledge financial support from the Spanish Ministry of Economy, Industry, and Competitiveness through the “Severo Ochoa” Program for Centers of Excellence in R&D (SEV‐2015‐0496), MAT2015‐70850‐P, and from the Generalitat de Catalunya through AGAUR 2018 PROD 00191; from CSIC through project 201560I032; and from the European Research Council (ERC) under grant agreement no. 648901. F.A., E.‐S.M.D., and H.S.R would like to acknowledge the Ministry of Higher Education (MOHE) of Egypt, the National Bank of Egypt and Banque Misr for funding the fellowship to conduct this study.Peer reviewe

Outdoor operation of small-molecule organic photovoltaics

We measure the diurnal dependence of the operating characteristics of tetraphenyldibenzoperiflanthene (DBP):C70 planar-mixed heterojunction small-molecule organic photovoltaic (OPV) cells with 2,2′,2″-(1,3,5-benzenitryl tris-[1-phenyl-1H-benzimidazole] (TPBi):C70 electron-filtering cathode buffer layers. Over the course of a day, efficiency gradually increases as a result of a concomitant increase in short-circuit current, while the fill factor and open-circuit voltage remain constant. The results are analyzed on the basis of independent measurements of temperature- and intensity-dependent OPV performance. The power conversion efficiency is maximized slightly below 1 sun intensity and at 40 °C, which is beneficial for practical outdoor operation. We attribute the increased short circuit current with temperature to broadening of the absorption spectrum due to population of phonon states along with increased charge mobility, which also results in an increase in fill factor.Peer Reviewe

Structure dependent photostability of ITIC and ITIC-4F†

Strong synthetic and engineering efforts have taken the efficiency of non-fullerene acceptor (NFA) based organic solar cells above 18% in a few years. Nonetheless, a deep understanding of the fundamental properties of this class of molecules is still missing. Here, we systematically investigated the morphological properties of two high efficient indacenodithienothiophene-based NFAs – namely ITIC and ITIC-4F – in order to correlate the hydrogen/fluorination substitutions with the materials structural and stability properties. We confirm that each NFA structurally evolves with increasing temperature into several polymorphs, identifying through spectroscopy their corresponding narrow temperature ranges. We demonstrate that the materials’ response to accelerated stress tests (ASTs) is both substitution and polymorph dependent. ASTs underlined that the most vulnerable molecular segment corresponds to the thienothiophene C[double bond, length as m-dash]C bond along the central backbone, together with the C[double bond, length as m-dash]C linkage between the electron-rich donor and the electron-deficient acceptor moieties, with a degradation process triggered by oxygen and light. ITIC-4F showed lower oxidation capability and a higher bond strength retaining effect compared to ITIC. Lastly, the AST approach employed here allowed for the extrapolation of morphological and stability-related features within a high-throughput framework, and can be considered as a valuable methodological tool for future stability-related studies.The authors would like to thank Dr Tommaso Salzillo and Dr Valentina Bulova for very fruitful scientific discussions. The authors kindly acknowledge the financial support from Ministerio de Economía y Competitividad of Spain through the “Severo Ochoa” Programme for Centres of Excellence in R&D and projects PGC2018-095411-B-I00 and PGC2018-094620-A-I00, as well as the European Research Council (ERC) under grant agreement no. 648901.Peer reviewe

A Liquid-Crystalline Non-Fullerene Acceptor Enabling HighPerformance Organic Solar Cells

cThe use of liquid crystalline (LC) compounds in organic photovoltaics has revealed to be an effective strategy to optimise the bulk heterojunction morphology, repairing structural defects through their self-assembling properties. Nonetheless, the design of LC materials has mostly been limited to donor molecules in previous reports. Here we introduce a Non-Fullerene Acceptor (NFA), 4TICO, characterised by an improved structural flexibility, which is imparted by the alkoxy sidechain and favours the formation of LC phases at high temperature. This structural polymorphism also occurs in films where the 4TICO is blended with the PBTZT-stat-BDTT-8 polymer. The high-temperature LC polymorph brings to the formation of a smooth surface morphology with less structural defects, providing solar cells with improved short-circuit current (Jsc) and fill factor (FF), by 14% and 20% respectively. An in-depth investigation of the NFA structural properties in relation to the solar cells performance and charge transport is carried out in comparison to the 4TIC crystalline isomer.P. M. and F. S. acknowledge the European Union’s Horizon 2020 research and innovation programme under Marie Skłodowska Curie Grant agreement no. 722651 (SEPOMO) for the support in the realization of this work. This work has been supported by the Spanish Government under the project PID2019-110907GB-I00, the “Severo Ochoa” Program for Centres of Excellence in R&D (CEX2019-000917-S) and by the European Union’s Horizon 2020 Research and Innovation Program under grant agreement no. 730872. E.B. and F.S. also acknowledge the Generalitat de Catalunya grant 2017 SGR668. P.M has carried out his work within the framework of the doctoral program (PhD) in Optics and Photonics of Condensed Matter Physics (Department of Physics) at the Chemnitz University of Technology and F. S. in Material Science (Department of Physics) at the Universitat Autònoma de Barcelona (UAB). GIWAXS experiments were performed at NCD-SWEET beamline at ALBA synchrotron (Beamtime ID: 2019093873) with the collaboration of ALBA staff. The authors thank Dr Pascal Kaienburg of the University of Oxford and Dr Mariano Campoy-Quiles of ICMAB for their valuable suggestions and fruitful discussions.Peer reviewe

Water splitting for hydrogen chemisorption in graphene oxide dynamically evolving to a graphane character lattice

Graphane offers a safe and high capacity hydrogen storage. Unfortunately, production of graphane directly from its parent material graphene requires breaking the extended p bond, implying either harsh chemical environments or highly energetic plasmas. In here, we propose to use graphene oxide (GO) to initially have the lattice irregularities and local curvature conferring to some of the carbons a favorable partial negative charge or a sp3 hybridization suitable for C–H bond formation. When GO covers the cathode of a water splitting cell powered at 1.7¿V, we demonstrate an effective hydrogen chemisorption exhibiting a logarithmic growth with time. Such GO undergoes a dynamic evolution, combining a continuous change in the local corrugation and partial charge distribution with deoxygenation, opening additional sites for hydrogen chemisorption. Using density functional theory combined with the experimental parameters we can monitor the H atom gravimetric density increase as the water splitting experiment takes place.Peer ReviewedPostprint (author's final draft