Semi-transparent polymer solar cells

Copyright 2015 Society of Photo Optical Instrumentation Engineers (SPIE). One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this publication for a fee or for commercial purposes, or modification of the contents of the publication are prohibited.Over the last three decades, progress in the organic photovoltaic field has resulted in some device features which make organic cells applicable in electricity generation configurations where the standard silicon-based technology is not suitable, for instance, when a semi-transparent photovoltaic panel is needed. When the thin film solar cell performance is evaluated in terms of the device's visible transparency and power conversion efficiency, organic solar cells offer the most promising solution. During the last three years, research in the field has consolidated several approaches for the fabrication of high performance semi-transparent organic solar cells. We have grouped these approaches under three categories: devices where the absorber layer includes near-infrared absorption polymers, devices incorporating one-dimensional photonic crystals, and devices with a metal cavity light trapping configuration. We herein review these approaches.Peer ReviewedPostprint (author's final draft

Enhanced stability in semi-transparent PTB7/PC71BM photovoltaic cells

© 2015. This version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/We studied the performance over time of opaque and semi-transparent PTB7:PC71BM bulk heterojunction solar cells. For unsealed inverted configuration cells we observe that when the isolation from the environment is improved, the degradation observed is dominated by one single exponential decay. We demonstrate that a dielectric multilayer stack of approximately 550 nm provides an isolation that increases the lifetime of the cell close to ten times. In that event the fill factor appears to be the PV parameter dominating cell degradation resulting from a decrease in the shunt resistance. An Impedance analysis we performed indicates that a Warburg element, attributed to the presence of slowly moving charges such as heavy ions, must be included in the description of the experimental data. The contribution from such element increases as the cell degrades in good agreement with a degradation dominated by the corrosive effects from external agents reaching the active layer of the device.Peer ReviewedPostprint (author's final draft

Catalitzadors de metàtesi recuperables per formació de materials híbrids orgànico-inorgànics

Les reaccions de metàtesi de diens i d'enins catalitzades per espècies carbèniques de ruteni constitueixen poderoses eines àmpliament utilitzades per a la síntesi d'una gran diversitat de productes. La importància de la reacció de metàtesi s'ha posat de manifest amb la concesió del premi Nobel de Química 2005 a Chauvin, Grubbs i Schrock. La recerca de catalitzadors més estables i actius i la preparació de catalitzadors reciclables han merescut els esforços d'un gran nombre de grups durant els últims anys. Grubbs i Hoveyda han introduït carbens N-heterocíclics (NHC) i lligands estirènics quelatants per a la millora dels sistemes catalítics. Una de les estratègies utilitzades per a la recuperació i reciclatge d'aquests sistemes catalítics és l'ancoratge de l'espècie homogènia a un suport polimèric insoluble, sent els polímers orgànics els més comuns. Dins dels inorgànics els treballs són menys nombrosos i corresponen a l'ancoratge a síliques comercials, a sistemes monolítics o a síliques mesoestructurades. La major estabilitat tèrmica, química i mecànica dels polímers inorgànics i les seves elevades àrees superficials els fan alternatives atractives per a la incorporació covalent de lligands orgànics i complexes metàlics. Com a alternativa a l'ancoratge, la part orgànica pot incorporar-se a la matriu inorgànica mitjançant el procés sol-gel. Els híbrids orgànico-inorgànics derivats de sílice obtinguts han experimentat un gran creixement durant la última dècada, amb el desenvolupament de sistemes organitzats en presència de tensioactius. En la present tesi doctoral s'han sintetitzat cinc monòmers diferents de tipus Hoveyda que presenten grups trietoxisilil. El primer és un equivalent del lligand quelatant original de Hoveyda que inclou una cadena espaiadora i un grup trietoxisilil. Altres monòmers són variacions on la cadena espaiadora inclou una urea enlloc d'un carbamat. Un d'ells conté a la seva estructura un grup nitro que ha de potenciar la seva activitat com a catalitzador, mentre que un altre es tracta d'un derivat bisililat, el qual permet la preparació de materials pel procés sol-gel sense que sigui necessària l'addició de tetraetoxisilà (TEOS). A partir dels diferents monòmers s'han sintetitzat materials híbrids orgànico-inorgànics per diversos procediments: procés sol-gel amb diferents quantitats deTEOS i fluorur com a catalitzador, en presència de dodecilamina, que actua com a agent estructurant i com a catalitzador a la vegada i, en el cas del derivat bisililat, també pel procés sol-gel en absència de TEOS. Els mateixos monòmers s'han ancorat a gel de sílice mesoestructurat MCM-41 i a gel de sílice comercial. Tots els materials s'han caracteritzat gràcies a la col·laboració amb el grup de Michel Wong Chi Man de la "Ecole Nationale Superieure de Chimie de Montpellier" mitjançant diferents tècniques: Ressonància magnètica nuclear de silici-29 en estat sòlid (que permet comprovar la unió covalent entre el lligand orgànic i la matriu sililada), mesures d'adorció-desorció de nitrogen pel mètode BET (amb les quals es determina la superfíce específica del material i la distribució dels diàmetres de porus), difracció de raigs X en pols (determinació de la possible estructuració del material), anàlisi elemental (quantitat de matèria orgànica incorporada) i microscopia electrònica de transmissió (TEM). S'observa que els materials presenten superfices específiques majors quan s'han utilitzat agents estructurant i quan la dilució de la part orgànica és major. El tractament dels materials híbrids amb els carbens de Grubbs de primera i/o segona generació ha donat lloc als corresponents catalitzadors suportats. Aquests s'han assajat en reaccions de metàtesi de diens per tal d'obtenir olefines di-, tri- i tetrasubstituides, i també en la metàtesi d'un ení.Dels resultats obtinguts es desprèn que els materials tractats amb el catalitzador de segona generació són els més eficaços i que els catalitzadors heterogènis que provenen de sol-gel són més actius i es reciclen millor que els corresponents a l'ancoratge a MCM-41 o a sílica comercial. En la síntesi de l'1-(4-toluensulfonil)-2,5-dihidro-1H-pirrole s'han realitzat fins a cinc cicles consecutius amb la majoria dels catalitzadors. Aquells materials que contenen el monòmer més semblant al lligand quelatant original de Hoveyda són els que donen una millor capacitat de reciclatge, mentre que els més actius són els que contenen el grup electroatraient nitro. Entre els catalitzadors preparats per sol-gel resulten ser més actius aquells que presenten una major superfície específica i una major dilució del lligand al seu interior. Els materials preparats a partir del monòmer bisililat sense la addició de TEOS presenten, malgrat tenir una superfície nula, una activitat comparable als altament porosos. En la síntesi de l'1-(4-toluensulfonil)-2,5-dihidro-3-metil-1H-pirrole s'han pogut realitzar fins a cinc cicles de catàlisi. Aquests resultats són millors que els descrits a la literatura amb catalitzadors suportats per a aquesta reacció. En la síntesi del 3,4-dimetil-1-(4-toluensulfonil)-2,5-dihidro-1H-pirrole s'han aconseguit realitzar fins a tres cicles amb un dels catalitzadors, i dos amb la majoria. Aquests resultats constitueixen el primer exemple reeixit de preparació d'aquesta olefina tetrasubstituida amb un catalitzador suportat i el primer cas on s'aconsegueix reutilitzar el catalitzador amb un cert èxit. En la metàtesi de l'ení 1-al·liloxi-1,1-difenil-2-propí s'han realitzar fins a cinc cicles amb la majoria dels catalitzadors. Els resultats constitueixen el primer exemple de recuperació d'un catalitzador en una reacció de matàtesi d'enins.The diene and enyne metathesis reactions catalyzed by ruthenium carbene species are powerful tools widely used by organic chemists for the synthesis of a great diversity of compounds. The great importance of the metathesis reaction has been made clear with the award of the Nobel Prize of Chemistry 2005 to Chauvin, Grubbs and Schrock. In the metathesis field a considerable number of groups in the last years have dedicated their efforts to the search of more stable and active carbene complexes and to the preparation of recoverable catalysts. Grubbs and Hoveyda have introduced N-heterocyclic carbenes (NHC) and chelating styrenic ligands for the improvement of catalytic systems. One of the strategies used for the recovery of the mentioned ruthenium and palladium catalytic systems is the anchorage of the homogeneous species to an insoluble polymeric support, organic polymers being the most commonly used. In the case of inorganic polymers the precedents are scarce and correspond to the anchoring to commercial silicas, monolithic systems or mesostructured silicas. The better thermal, chemical and mechanical stability of inorganic polymers and their high surface areas make them attractive alternatives for the covalent incorporation of organic ligands and metallic complexes. As an alternative to the anchoring method, the organic moiety can be incorporated to the inorganic matrix by the sol-gel process. The silica-based organic-inorganic hybrids obtained by sol-gel have experienced a great boom in the last decade, with the development of organized systems in the presence of surfactants. In this doctoral thesis five Hoveyda-type monomers have been synthesized containing a triethoxysilil group. The first one is equivalent to the original Hoveyda quelating ligand, and includes a spacing chain and a triethoxysilil group. Other monomers have a urea instead of a carbamate as the spacing chain. One of them contains a nitro group which is expected to improve the catalyst activity, whereas another one is a bisililated derivative, which can be used to prepare materials through the sol-gel process without addition of TEOS being necessary. These monomers have been used to prepare organic-inorganic hybrid materials through several strategies: sol-gel process with different TEOS amounts and fluoride as catalyst, dodecilamine acting both as structurating agent and catalyst and, in the case of the bisililated monomer, through the sol-gel process without TEOS being added. The same monomers have been anchored to commercial and to mesostructurated MCM-41 silica gel. All of them have been characterized in collaboration with Michel Wong Chi Man, from the "Ecole Nationale Superieure de Chimie de Montpellier" through several techniques: Solid state 29Si-NMR (in order to verify the covalent bond between the organic moiety and the sililated matrix), BET nitrogen adsorption-desorption measures (specific surface area and pore size distribution of the material) X ray diffraction (possible material structuration), elemental analysis (amount of incorporated organic moiety) and transmission electron microscopy (TEM). Higher surface areas are observed when structurating agents have been used and with the higher dilution of the organic moiety. Treatment of the hybrid materials with Grubbs first and/or second generation carbenes has produced the corresponding supported catalysts. They have been used in diene metathesis reactions leading to di-, tri- and tetrasubstituted olefins, and in an enyne metathesis reaction, too. The results show that the materials treated with the second generation catalyst are the most efficient and that those synthesized by the sol-gel process are more active and more reusable than those obtained by anchoring either to MCM-41 or to commercial silica gel. In the synthesis of 1-(4-toluensulfonyl)-2,5-dihidro-1H-pirrole five consecutive runs have been performed with most of the catalysts. Those materials containing the most similar monomer to the Hoveyda quelating ligand show the best recycling capacity, whereas the more active ones are those with the electron withdrawing nitro group. Among the catalysts prepared by sol-gel, those with higher surface areas and higher dilution of the ligand in the sililated matrix are the more active. The materials prepared with the bisililated monomer without TEOS addition, although having no surface area at all, show a similar activity than the highly porous ones. In the synthesis of 1-(4-toluensulfonyl)-2,5-dihidro-3-methyl-1H-pirrole five consecutive runs have been performed. The results are better than those described in the literature with supported catalysts for this reaction. In the synthesis of 3,4-dimethyl-1-(4-toluensulfonyl)-2,5-dihidro-1H-pirrole three runs have been performed with one of the catalysts, and two with most of the other. These results are the first successful example for the preparation of this tetrasubstituted olefin with a supported catalyst and the first where it has been reused with a certain success. In the metathesis of 1-allyloxi-1,1-diphenyl-2-propyne five runs have been performed with most of the catalysts. The results obtained constitute the first example of recycling of a catalyst in an enyne metathesis reaction

Transparent polymer solar cells emplotings a layered light-trapping architecture

Organic solar cells have unique properties that make them very attractive as a renewable energy source. Of particular interest are semi-transparent cells, which have the potential to be integrated into building fac¸ades yet not completely block light. However, making organic cells transparent limits the metal electrode thickness to a few nanometres, drastically reducing its reflectivity and the device photon-harvesting capacity. Here, we propose and implement an ad hoc path for light-harvesting recovery to bring the photon-to-charge conversion up to almost 80% that of its opaque counterpart. We report semi-transparent PTB7:PC71BM cells that exhibit 30% visible light transmission and 5.6% power conversion efficiency. Non-periodic photonic crystals are used to trap near-infrared and near-ultraviolet photons. By modifying the layer structure it is possible to tune the device colour without significantly altering cell performance.Peer Reviewe

Neutral water splitting catalysis with a high FF triple junction polymer cell

This document is the Accepted Manuscript version of a Published Work that appeared in final form in CS catalysis, copyright © American Chemical Society, after peer review and technical editing by the publisher and may be found at http://dx.doi.org/10.1021/acscatal.6b01036We report a photovoltaics-electrochemical (PV-EC) assembly based on a compact and easily processable triple homojunction polymer cell with high fill factor (76%), optimized conversion efficiencies up to 8.7%, and enough potential for the energetically demanding water splitting reaction (V-oc = 2.1 V). A platinum-free cathode made of abundant materials is coupled to a ruthenium oxide on glassy carbon anode (GC-RuO2) to perform the reaction at optimum potential (Delta E = 1.70-1.78 V, overpotential = 470-550 mV). The GC-RuO2 anode contains a single monolayer of catalyst corresponding to a superficial concentration (Gamma) of 0.15 nmol cm(-2) and is highly active at pH 7. The PV-EC cell achieves solar to hydrogen conversion efficiencies (STH) ranging from 5.6 to 6.0%. As a result of the solar cell's high fill factor, the optimal photovoltaic response is found at 1.70 V, the minimum potential at which the electrodes used perform the water splitting reaction. This allows generating hydrogen at efficiencies that would be very similar (96%) to those obtained as if the system were to be operating at 1.23 V, the thermodynamic potential threshold for the water splitting reaction.Peer Reviewe

Semi-transparent polymer solar cells

Copyright 2015 Society of Photo Optical Instrumentation Engineers (SPIE). One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this publication for a fee or for commercial purposes, or modification of the contents of the publication are prohibited.Over the last three decades, progress in the organic photovoltaic field has resulted in some device features which make organic cells applicable in electricity generation configurations where the standard silicon-based technology is not suitable, for instance, when a semi-transparent photovoltaic panel is needed. When the thin film solar cell performance is evaluated in terms of the device's visible transparency and power conversion efficiency, organic solar cells offer the most promising solution. During the last three years, research in the field has consolidated several approaches for the fabrication of high performance semi-transparent organic solar cells. We have grouped these approaches under three categories: devices where the absorber layer includes near-infrared absorption polymers, devices incorporating one-dimensional photonic crystals, and devices with a metal cavity light trapping configuration. We herein review these approaches.Peer Reviewe

Enhanced stability in semi-transparent PTB7/PC71BM photovoltaic cells

© 2015. This version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/We studied the performance over time of opaque and semi-transparent PTB7:PC71BM bulk heterojunction solar cells. For unsealed inverted configuration cells we observe that when the isolation from the environment is improved, the degradation observed is dominated by one single exponential decay. We demonstrate that a dielectric multilayer stack of approximately 550 nm provides an isolation that increases the lifetime of the cell close to ten times. In that event the fill factor appears to be the PV parameter dominating cell degradation resulting from a decrease in the shunt resistance. An Impedance analysis we performed indicates that a Warburg element, attributed to the presence of slowly moving charges such as heavy ions, must be included in the description of the experimental data. The contribution from such element increases as the cell degrades in good agreement with a degradation dominated by the corrosive effects from external agents reaching the active layer of the device.Peer Reviewe

Evaluation of a quality improvement intervention to reduce anastomotic leak following right colectomy (EAGLE): pragmatic, batched stepped-wedge, cluster-randomized trial in 64 countries

Background Anastomotic leak affects 8 per cent of patients after right colectomy with a 10-fold increased risk of postoperative death. The EAGLE study aimed to develop and test whether an international, standardized quality improvement intervention could reduce anastomotic leaks. Methods The internationally intended protocol, iteratively co-developed by a multistage Delphi process, comprised an online educational module introducing risk stratification, an intraoperative checklist, and harmonized surgical techniques. Clusters (hospital teams) were randomized to one of three arms with varied sequences of intervention/data collection by a derived stepped-wedge batch design (at least 18 hospital teams per batch). Patients were blinded to the study allocation. Low- and middle-income country enrolment was encouraged. The primary outcome (assessed by intention to treat) was anastomotic leak rate, and subgroup analyses by module completion (at least 80 per cent of surgeons, high engagement; less than 50 per cent, low engagement) were preplanned. Results A total 355 hospital teams registered, with 332 from 64 countries (39.2 per cent low and middle income) included in the final analysis. The online modules were completed by half of the surgeons (2143 of 4411). The primary analysis included 3039 of the 3268 patients recruited (206 patients had no anastomosis and 23 were lost to follow-up), with anastomotic leaks arising before and after the intervention in 10.1 and 9.6 per cent respectively (adjusted OR 0.87, 95 per cent c.i. 0.59 to 1.30; P = 0.498). The proportion of surgeons completing the educational modules was an influence: the leak rate decreased from 12.2 per cent (61 of 500) before intervention to 5.1 per cent (24 of 473) after intervention in high-engagement centres (adjusted OR 0.36, 0.20 to 0.64; P < 0.001), but this was not observed in low-engagement hospitals (8.3 per cent (59 of 714) and 13.8 per cent (61 of 443) respectively; adjusted OR 2.09, 1.31 to 3.31). Conclusion Completion of globally available digital training by engaged teams can alter anastomotic leak rates. Registration number: NCT04270721 (http://www.clinicaltrials.gov)