Embedment of metal nanoparticles in GaAs and Si for plasmonic absorption enhancement in intermediate band solar cells

The high near-field enhancement occurring in the vicinity of metallic nanoparticles (MNPs) sustaining surface plasmons can only be fully exploited in photovoltaic devices if the MNPs are placed inside their semiconducting material, in the photoactive region. In this work an experimental procedure is studied to embed MNPs in gallium arsenide (GaAs) and silicon (Si), which can be applied to other semiconductor host materials. The approach consists in spin-coating colloidal MNPs dispersed in solution onto the substrate surface. Then a capping layer of the same material as the substrate is deposited on top to embed the MNPs in the semiconductor. The extinction spectra of silver (Ag) and gold (Au) MNPs embedded in GaAs and Si is modeled with Mie theory for comparison with optical measurements. This contribution constitutes the initial step towards the realization of quantum-dot intermediate band solar cells (QD-IBSC) with MN

Raising the Efficiency Limit of the GaAs-based Intermediate Band Solar Cell Through the Implementation of a Mololithic Tandem with an AlGaAs top Cell.

The high efficiency limit of the intermediate band solar cell (IBSC) corresponds to the case of using as intermediate band (IB) host material a semiconductor with gap in the range of 2 eV. Traditional photovoltaic materials, such as Si and GaAs, are not appropriate to produce IB devices because their gaps are too narrow. To overcome this problem, we propose the implementation of a multi-junction device consisting of an IBSC combined with a single gap cell. We calculate the efficiency limits using the detailed balance model and conclude that they are very high (> 60% under maximum concentration) for any fundamental bandgap from 0.7 to 3.6 eV in the IBSC inserted in the tandem. In particular, the two-terminal tandem of a GaAs-based IBSC current matched to an optimized AlGaAs top cell has an efficiency limit as high as 64%

Componente de indexación de huellas dactilares basado en características globales

The fingerprint orientation field is a widely used feature for developing indexing strategies. Such feature brings stability and decreases the response times during the identification process. The use of attribute relational graphs and dynamic masks can exploit the features provided by the partitioning scheme. The penetration index and the error rate for each of the proposed strategies were determined. To verify the results obtained were used the databases provided by the Fingerprint Verification Competition. Both search schemes reveal the facilities offered by the orientation field for guiding the searching process; reducing the number of comparisons in 53.24%; proving its stability against different fingerprint image qualities. Based on the results, it was proven that the adoption of such indexing strategies will reduce the response time in the identification module proposed by the Identification and Digital Security Center at the University of Informatics Sciences.El campo de orientación de la huella dactilar como característica global es fundamental para el desarrollo de una estrategia de indexación, aportando estabilidad y disminuyendo los tiempos de respuesta durante el proceso de búsqueda de un sistema de identificación basado en huellas dactilares. El empleo de grafos relacionales de atributos y máscaras dinámicas permite explotar las características brindadas por el esquema de particionado para la búsqueda. De cada una de las estrategias propuestas se determinó el índice de penetración de la base de datos, así como el error en que incurren los algoritmos de indexación implementados. Para corroborar los resultados obtenidos fueron empleados los bancos de datos aportados por la Competencia de verificación de huellas dactilares. La implementación computacional de las estrategias de búsquedas propuestas demuestra las virtudes que ofrece el campo de orientación para dirigir el proceso de búsqueda, logrando reducir el número de comparaciones en un 53.24% como promedio, comportándose de manera estable ante imágenes de huellas dactilares de diferente calidad. Basado en los resultados del estudio se concluyó que la adopción de dichas estrategias de indexación permitirá reducir el tiempo de respuesta en el módulo de identificación de individuos basado en patrones de la huella dactilar propuesto por el Centro de Identificación y Seguridad Digital de la Universidad de las Ciencias Informáticas

Modelling and Characterization of Multiple Level Intermediate Band Solar Cell

Intermediate band solar cells (IBSCs) are a new kind of devices capable of surpassing the Shockley Queisser efficiency limit for conventional solar cells. This novel technology requires the use of a new type of material named intermediate band (IB) material which makes a better use of the solar spectrum thanks to the existence of a collection of electronic levels within the band gap of the semiconductor. Quantum Dots (QDs) remain as a feasible technology to implement IB materials. InAs/GaAs QD-IBSCs were manufactured in order to test the validity of the concept, although their real size and shape are far from the optimum. This causes extra electron levels to appear within the nanostructure confining potential, degrading the performance of the device. In this paper, the effect of these extra levels will be studied through a multiple level IBSC model based on the detailed balance, but modified so a term accounting for the non-radioactive recombination (NRR) is also included. The model is completed with constant fitting parameters so the concentration JL-VOC curves (which do not incorporate series resistance effects) can be fitted. Several QD-IBSCs where manufactured, measured and fitted with this model, rendering relevant information about the recombination nature of the QD-IBSC

Modeling and characterization of multiple level intermediate band solar cell

Intermediate band solar cells (IBSCs) are a new kind of devices capable of surpassing the Shockley Queisser efficiency limit for conventional solar cells. This novel technology requires the use of a new type of material named intermediate band (IB) material which makes a better use of the solar spectrum thanks to the existence of a collection of electronic levels within the band gap of the semiconductor. Quantum Dots (QDs) remain as a feasible technology to implement IB materials. InAs/GaAs QD-IBSCs were manufactured in order to test the validity of the concept, although their real size and shape are far from the optimum. This causes extra electron levels to appear within the nanostructure confining potential, degrading the performance of the device. In this paper, the effect of these extra levels will be studied through a multiple level IBSC model based on the detailed balance, but modified so a term accounting for the non-radiative recombination (NRR) is also included. The model is completed with constant fitting parameters so the concentration JL-VOC curves (which do not incorporate series resistance effects) can be fitted. Several QD-IBSCs where manufactured, measured and fitted with this model, rendering relevant information about the recombination nature of the QD-IBSCs

Valoración del interés manifestado por las enfermeras asistenciales acerca de disponer de un cuestionario de evaluación enfermera de las capacidades comunicativas en la afasia

La afasia es el trastorno de los procesos implicados en la expresión y comprensión del lenguaje secundario a un daño cerebral adquirido. La afasia genera un gran impacto sobre la calidad de vida, afectando al desarrollo de las ABVD. Objetivo: evaluar el interés que manifiestan las enfermeras por disponer de un instrumento de fácil aplicación, que evalúe, según áreas de interés para el cuidado, las capacidades comunicativas en pacientes con afasia. Método: estudio descriptivo mediante una encuesta administrada a 70 enfermeras de diferentes ám-bitos de atención. Resultados: el 50% de las enfermeras manifestaron que este instrumento resultaría de bastante utilidad, con un alto nivel de aplicabilidad. Conclusión: este estudio apoya la necesidad de un instrumento enfermero con las características planteadas.Aphasia is the disorder of the processes involved in the formulation and interpreting lan-guage secondary to acquired brain damage. Aphasia has a great impact on quality of life, affecting the development of ABVD. Objective: to explore the interest expressed by nurses in having an easy-to-apply instrument that assesses, according to areas of interest for care, communication skills in patients with aphasia. Method: Descriptive study through a survey administered to 70 nurses from different healthcare settings. Results: 50% of nurses reported that this instrument would be quite useful with a high level of applicability in healthcare practice. Conclusion: This preliminary study supports the need for a nursing instrument with the proposed characteristics

Understanding the operation of quantum dot intermediate band solar cells

In this paper, a model for intermediate band solar cells is built based on the generally understood physical concepts ruling semiconductor device operation, with special emphasis on the behavior at low temperature. The model is compared to JL-VOC measurements at concentrations up to about 1000 suns and at temperatures down to 20 K, as well as measurements of the radiative recombination obtained from electroluminescence. The agreement is reasonable. It is found that the main reason for the reduction of open circuit voltage is an operational reduction of the bandgap, but this effect disappears at high concentrations or at low temperatures

Intermediate band solar energy conversion in ZnTeO

Energy conversion in solar cells incorporating ZnTeO base layers is presented. The ZnTeO base layers incorporate intermediate electronic states located approximately 0.4eV below the conduction band edge as a result of the substitution of O in Te sites in the ZnTe lattice. Cells with ZnTeO base layers demonstrate optical response at energies lower than the ZnTe bandedge, a feature that is absent in reference cells with ZnTe base layers. Quantum efficiency is significantly improved with the incorporation of ZnSe emitter/window layers and transition from growth on GaAs substrates to GaSb substrates with a near lattice match to ZnTe

Self-organized colloidal quantum dots and metal nanoparticles for plasmon-enhanced intermediate-band solar cells

A colloidal deposition technique is presented to construct long-range ordered hybrid arrays of self-assembled quantum dots and metal nanoparticles. Quantum dots are promising for novel opto-electronic devices but, in most cases, their optical transitions of interest lack sufficient light absorption to provide a significant impact in their implementation. A potential solution is to couple the dots with localized plasmons in metal nanoparticles. The extreme confinement of light in the near-field produced by the nanoparticles can potentially boost the absorption in the quantum dots by up to two orders of magnitude. In this work, light extinction measurements are employed to probe the plasmon resonance of spherical gold nanoparticles in lead sulfide colloidal quantum dots and amorphous silicon thin-films. Mie theory computations are used to analyze the experimental results and determine the absorption enhancement that can be generated by the highly intense near-field produced in the vicinity of the gold nanoparticles at their surface plasmon resonance. The results presented here are of interest for the development of plasmon-enhanced colloidal nanostructured photovoltaic materials, such as colloidal quantum dot intermediate-band solar cells