Mixed AgBiS2 nanocrystals for photovoltaics and photodetectors

Heavy-metal-free colloidal nanocrystals are gaining due attention as low-cost, semiconducting materials for solution-processed optoelectronic applications. One common limitation of such materials is their limited carrier transport and trap-assisted recombination, which impede the performance of thick photoactive layers. Here we mix small-size and large-size AgBiS2 nanocrystals to judiciously favour the band alignment in photovoltaic and photodetector devices. The absorbing layer of these devices is fabricated in a gradient fashion in order to maximise charge transfer and transport. We implement this strategy to fabricate mixed AgBiS2 thin film solar cells with a power conversion of 7.3%, which significantly surpasses the performance of previously reported devices based on single-batch AgBiS2 nanocrystals. Additionally, this approach allows us to fabricate devices using thicker photoactive layers that show lower dark currents and external quantum efficiencies exceeding 40% over a broad bandwidth – covering the visible and near infrared range beyond 1 μm, thus unleashing the potential of colloidal AgBiS2 nanocrystals in photodetector applications.Peer ReviewedPostprint (published version

High Performance Inverted Organic Photovoltaics Without Hole Selective Contact

A detailed investigation of the functionality of inverted organic photovoltaics (OPVs) using bare Ag contacts as top electrode is presented. The inverted OPVs without hole transporting layer (HTL) exhibit a significant gain in hole carrier selectivity and power conversion efficiency (PCE) after exposure in ambient conditions. Inverted OPVs comprised of ITO/ZnO/poly(3-hexylthiophene-2,5-diyl):phenyl-C61-butyric acid methyl ester (P3HT:PCBM)/Ag demonstrate over 3.5% power conversion efficiency only if the devices are exposed in air for over 4 days. As concluded through a series of measurements, the oxygen presence is essential to obtain fully operational solar cell devices without HTL. Moreover, accelerated stability tests under damp heat conditions (RH=85% and T=65oC) performed to non-encapsulated OPVs demonstrate that HTL-free inverted OPVs exhibit comparable stability to the reference inverted OPVs. Importantly, it is shown that bare Ag top electrodes can be efficiently used in inverted OPVs using various high performance polymer:fullerene bulk heterojunction material systems demonstrating 6.5% power conversion efficiencies

High‐Volume Processed, ITO‐Free Superstrates and Substrates for Roll‐to‐Roll Development of Organic Electronics

The fabrication of substrates and superstrates prepared by scalable roll‐to‐roll methods is reviewed. The substrates and superstrates that act as the flexible carrier for the processing of functional organic electronic devices are an essential component, and proposals are made about how the general availability of various forms of these materials is needed to accelerate the development of the field of organic electronics. The initial development of the replacement of indium‐tin‐oxide (ITO) for the flexible carrier materials is described and a description of how roll‐to‐roll processing development led to simplification from an initially complex make‐up to higher performing materials through a more simple process is also presented. This process intensification through process simplification is viewed as a central strategy for upscaling, increasing throughput, performance, and cost reduction

Organic photovoltaic cells – promising indoor light harvesters for self-sustainable electronics

Photovoltaic cells are attracting significant interest for harvesting indoor light for low power consumption wireless electronics such as those required for smart homes and offices, and the rapidly-growing Internet of Things. Here, we explore the potential of solution processable, small molecule photovoltaic cells as indoor power sources. By optimizing solvent vapour annealing (SVA) time to the photovoltaic layer, a balance between its crystallization and phase separation is obtained, resulting in a record power conversion efficiency of over 28 % under fluorescent lamps of 1000 lux, generating a maximum power density of 78.2 µW/cm2 (>10 % efficiency under AM1.5G). This high indoor performance surpasses silicon based photovoltaic cells, and is similar to gallium arsenide photovoltaic cells. Besides, the ratios of the voltage at maximum power point to the open circuit voltage are similar from indoor lighting to one sun condition, which is unique and allows a less power consuming method to track the maximum power point for a broad range of light intensities (potentially attractive for wearable PV). New insight on the effect of SVA to the indoor and one sun performance is provided by advanced optoelectronic characterization techniques, which shows that the mobility-lifetime products as a function of charge carrier density can be correlated well to the performance at different light levels. Our results suggest that organic photovoltaic cell could be promising as indoor power source for self-sustainable electronics

Seguimiento de las guías españolas para el manejo del asma por el médico de atención primaria: un estudio observacional ambispectivo

Objetivo Evaluar el grado de seguimiento de las recomendaciones de las versiones de la Guía española para el manejo del asma (GEMA 2009 y 2015) y su repercusión en el control de la enfermedad. Material y métodos Estudio observacional y ambispectivo realizado entre septiembre del 2015 y abril del 2016, en el que participaron 314 médicos de atención primaria y 2.864 pacientes. Resultados Utilizando datos retrospectivos, 81 de los 314 médicos (25, 8% [IC del 95%, 21, 3 a 30, 9]) comunicaron seguir las recomendaciones de la GEMA 2009. Al inicio del estudio, 88 de los 314 médicos (28, 0% [IC del 95%, 23, 4 a 33, 2]) seguían las recomendaciones de la GEMA 2015. El tener un asma mal controlada (OR 0, 19, IC del 95%, 0, 13 a 0, 28) y presentar un asma persistente grave al inicio del estudio (OR 0, 20, IC del 95%, 0, 12 a 0, 34) se asociaron negativamente con tener un asma bien controlada al final del seguimiento. Por el contrario, el seguimiento de las recomendaciones de la GEMA 2015 se asoció de manera positiva con una mayor posibilidad de que el paciente tuviera un asma bien controlada al final del periodo de seguimiento (OR 1, 70, IC del 95%, 1, 40 a 2, 06). Conclusiones El escaso seguimiento de las guías clínicas para el manejo del asma constituye un problema común entre los médicos de atención primaria. Un seguimiento de estas guías se asocia con un control mejor del asma. Existe la necesidad de actuaciones que puedan mejorar el seguimiento por parte de los médicos de atención primaria de las guías para el manejo del asma. Objective: To assess the degree of compliance with the recommendations of the 2009 and 2015 versions of the Spanish guidelines for managing asthma (Guía Española para el Manejo del Asma [GEMA]) and the effect of this compliance on controlling the disease. Material and methods: We conducted an observational ambispective study between September 2015 and April 2016 in which 314 primary care physicians and 2864 patients participated. Results: Using retrospective data, we found that 81 of the 314 physicians (25.8%; 95% CI 21.3–30.9) stated that they complied with the GEMA2009 recommendations. At the start of the study, 88 of the 314 physicians (28.0%; 95% CI 23.4–33.2) complied with the GEMA2015 recommendations. Poorly controlled asthma (OR, 0.19; 95% CI 0.13–0.28) and persistent severe asthma at the start of the study (OR, 0.20; 95% CI 0.12–0.34) were negatively associated with having well-controlled asthma by the end of the follow-up. In contrast, compliance with the GEMA2015 recommendations was positively associated with a greater likelihood that the patient would have well-controlled asthma by the end of the follow-up (OR, 1.70; 95% CI 1.40–2.06). Conclusions: Low compliance with the clinical guidelines for managing asthma is a common problem among primary care physicians. Compliance with these guidelines is associated with better asthma control. Actions need to be taken to improve primary care physician compliance with the asthma management guidelines

Towards industrial viability of organic solar cells: ITO-free, green solvents and technological aspects for upscalability

Des de la seva aparició com a alternativa per la conversió d’energia fotovoltaica, el camp de les cel·les solars orgàniques ha experimentat un progrés significatiu, especialment en els darrers 15 anys. El gran interès en la tecnologia fotovoltaica orgànica (OPV, per les sigles en anglès) es deu principalment al seu potencial baix cost. Rellevants avenços científics han empès les eficiències de conversió energètica fins al 12%, fet que encoratja a acostar les OPV al mercat. Tanmateix, altres aspectes decisius per la seva industrialització han estat menys atesos. Aquesta tesi tracta tres qüestions clau que la tecnologia OPV ha d’afrontar per tal d’assolir una transferència fiable del laboratori a la industria. En primer lloc, es necessiten estratègies pel processat i post-processat a gran escala, idealment amb un cost reduït. En aquest treball es presenta una amplia investigació en inkjet printing. És necessari tenir un profund coneixement d’aquesta tècnica compatible amb roll-to-roll per tal d’assolir morfologies de capa adequades. S’ha trobat que la cinètica d’assecat de les capes és especialment crítica. En relació a això, s’ha desenvolupat un nou mètode per determinar patrons d’impressió apropiats per la deposició de la capa activa. A més, s’ha demostrat l’ús d’un tractament alternatiu anomenat vapour printing en dispositius OPV. Utilitzant aquest mètode amb vapor de dissolvent adequat, el tractament de la capa activa es pot assolir en temps molt més curts en comparació a altres tècniques. Un altre aspecte que ha estat poc atès està relacionat amb els dissolvents utilitzats pel processat dels OPV, especialment per la deposició de la capa activa. Típicament s’utilitzen dissolvents halogenats, com el clorbenzè o el diclorbenzè, essent alguns d’ells prohibits per aplicacions industrials. Substituir-los per formulacions verdes és, per tant, una necessitat primordial. Per tal de trobar sistemes aptes de dissolvents verds, s’ha utilitzat un mètode basat en la solubilitat. Aquest mètode, prèviament demostrat per cel·les solars polimèriques, s’estén de manera satisfactòria en aquesta tesi en dispositius basats en petita molècula. També s’aporten nous coneixements sobre la precisió del mètode. L’oxid d’indi i estany (ITO, per les seves sigles en anglès), freqüentment utilitzat com a elèctrode conductor transparent, contribueix de manera important en el cost d’un mòdul OPV. Altres raons per reemplaçar aquest component inclouen la seva modesta flexibilitat i conductivitat, el que pot limitar l’extracció de corrent elèctric en dispositius de gran àrea. Una possible alternativa són les xarxes metàl·liques combinades amb una capa transparent semiconductora. Tot i resoldre l’aspecte de la conductivitat, altres factors limiten encara l’extracció de corrent. El nou mètode utilitzat en aquest treball per preparar aquestes estructures venç aquests factors. Es demostren dispositius eficients lliures de ITO.Desde su aparición como alternativa para la conversión de energía fotovoltaica, el campo de las células solares orgánicas ha experimentado un progreso significativo, especialmente en los últimos 15 años. El gran interés en la tecnología fotovoltaica orgánica (OPV, por sus siglas en inglés) se debe principalmente a su potencial bajo coste. Relevantes avances científicos han empujado las eficiencias de conversión energética hasta el 12%, lo que alienta el acercamiento de las OPV al mercado. Sin embargo, otros aspectos decisivos para su industrialización han sido menos atendidos. Esta tesis trata tres cuestiones clave que la tecnología OPV tiene que afrontar para alcanzar una transferencia fiable del laboratorio a la industria. En primer lugar, se necesitan estrategias para el procesado y post-procesado a gran escala, idealmente con un coste reducido. En este trabajo se presenta una amplia investigación en inkjet printing. Es necesario tener un profundo conocimiento sobre esta técnica compatible con roll-to-roll para obtener morfologías de capa adecuadas. Se ha encontrado que la cinética de secado de la capa es especialmente crítica. En relación a esto, se ha desarrollado un nuevo método para determinar patrones de impresión adecuados para la deposición de la capa activa. Además, se ha demostrado el uso de un tratamiento alternativo llamado vapour printing en dispositivos OPV. Utilizando este método con vapores de disolvente aptos, el tratamiento de la capa activa se puede alcanzar en tiempos mucho más cortos en comparación con otras técnicas. Otro aspecto que ha sido poco atendido está relacionado con los disolventes utilizados en el procesado de las OPV, especialmente en la deposición de la capa activa. Típicamente se emplean disolventes halogenados, como el clorobenceno o diclorobenzeno, estando alguno de ellos prohibidos en aplicaciones industriales. Su substitución por formulaciones verdes es, por tanto, una necesidad primordial. Para encontrar sistemas aptos de disolventes verdes, se ha utilizado un método basado en la solubilidad. Este método, previamente demostrado para células solares poliméricas, se extiende de manera exitosa en esta tesis para dispositivos basados en pequeña molécula. También se aportan nuevos conocimientos sobre la precisión del método. El óxido de indio y estaño (ITO, por sus siglas en inglés), frecuentemente utilizado como electrodo conductor transparente, contribuye de manera importante en el coste de un módulo OPV. Otros motivos para substituir este componente incluyen su modesta flexibilidad y conductividad, lo que puede limitar la extracción de corriente eléctrica en dispositivos de gran área. Una posible alternativa son las redes metálicas combinadas con una capa transparente semiconductora. A pesar de que el aspecto de la conductividad queda solucionado, otros factores limitan aún la extracción de corriente. El nuevo método utilizado en este trabajo para preparar estas estructuras vence estos aspectos. Se demuestran dispositivos eficientes libres de ITO.Since its emergence as an alternative for photovoltaic energy conversion, the field of organic solar cells has experienced significant progress, especially in the last 15 years. The high interest in organic photovoltaics (OPV) technology is mostly due to its lowcost potential. Relevant scientific advances have pushed power conversion efficiencies up to 12%, which is encouraging for bringing OPV to market. However, other decisive aspects for their industrialisation have been less attended. This thesis deals with three key issues that OPV technology has to face in order to achieve a reliable lab-to-fab transfer. First, approaches for large-scale processing and post-processing are needed, ideally with reduced cost. In this work a broad investigation in inkjet printing is presented. A deep understanding on this roll-to-roll compatible technique is necessary to achieve suitable layer morphology. The drying kinetics of the wet film has been found to be especially critical. In relation to this, a new method to determine appropriate printing patterns for active layer deposition has been developed. Moreover, an alternative post-processing treatment called vapour printing is demonstrated for OPV devices. Using this method with suitable solvent vapour, the annealing of the active layer can be achieved in much shorter times as compared to other treatments. Another aspect that has been poorly attended is related to the solvents used for OPV processing, specifically for active layer deposition. Typically halogenated solvents such as chlorobenzene or o-dichlorobenzene are employed, being some of them banned for industrial applications. Their replacement by green formulations is therefore a major need. In order to find suitable green solvent systems, a method based on solubility has been used. This method, previously demonstrated for polymeric solar cells, is successfully extended in this thesis for small molecule based devices. New insights into the accuracy of the method are also provided. A major contributor to the cost of an OPV module is the indium-tin-oxide (ITO), commonly used as a transparent conductive electrode. Further reasons to replace this component include its modest flexibility and conductivity, which may limit current extraction in large area devices. One possible alternative are metallic grids combined with a transparent semiconductor layer. Although the conductivity issue is solved, other factors still limit current extraction. The new method used in this work to prepare such structures overcomes these features. Efficient, ITO-free devices are demonstrated