Publication: Fabricación de nanocontactos para células solares: invisibilidad y resonancias plasmónicas
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2016-07-05
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Universidad Complutense de Madrid
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Abstract
Los dispositivos opto-electrónicos, tales como las células solares, las pantallas planas y los diodos LED (del inglés light emitting diodes), necesitan contactos eléctricos en la cara frontal por la que entra o sale la luz del dispositivo. Estos contactos causan pérdidas por reflexión y absorción de luz (sombra) y por resistencia eléctrica. En una primera aproximación estas pérdidas son contrapuestas, lo que mejora la sombra empeora la resistencia y viceversa. Hasta ahora esto se ha entendido como un compromiso inevitable que limita la eficiencia de conversión energética de los dispositivos opto-electrónicos: disminuir las pérdidas por resistencia eléctrica implica necesariamente aumentar las pérdidas ópticas por sombra. Esta tesis se ha encaminado a tratar de superar esta dificultad a través de la nanoestructuración de la malla de contacto frontal, con especial énfasis en el caso de las células solares de concentración. El objetivo es poder reducir simultáneamente las pérdidas por sombreado y resistencia en serie de la malla. Hemos encontrado, en base a experimentos, teoría y simulaciones, que para tamaños de linea pequeños, en el umbral del régimen de Rayleigh, pero no lo suficientemente pequeños como para que se den las resonancias plasmónicas más intensas (de tipo dipolar), los contactos hacen menos sombra de la que corresponde a su área geométrica. Se puede decir que los contactos se vuelven parcialmente invisibles. En una primera parte de introducción se ha presentado la influencia de la malla en las pérdidas por resistencia en serie producidas en la célula. Se ha analizado el peso de las distintas variables y se ha escogido la reducción del espaciado entre líneas como alternativa a desarrollar. Para no afectar a otras variables, se ha reducido acordemente la anchura de línea manteniendo el factor de sombra geométrico de las células estado del arte. Se ha calculado que para un caso ideal la ganancia puede ser de un 4% absoluto para mallas con líneas de anchura 400-600 nm distribuidas en periodos de 10-20 μm. Se ha visto como otros efectos eléctricos apuntan también a ese rango como óptimo...
Optoelectronic devices such as solar cells, flat panes and LEDs need electrical contacts on the front surface through which light enters or leaves. These contacts cause losses due to light absorption and reflection (shadowing) and electrical resistance. To a first approximation both losses are opposed in the sense that what improves shadowing worsens resistance and viceversa. This has been understood as an unavoidable compromise that limits the final energy conversion efficiency: reducing electrical losses necessarily means increasing optical shadowing losses. This thesis has dealt with the overcoming of this limitation through the nanostructuration of the font contact grid, with special attention to the case of concentrating photovoltaics (CPV). The objective is to simultaneously reduce grid related shadowing and series resistance losses. Based on theory, computer simulations and experiments we have found that for small grid-finger dimensions, on the onset of the Rayleigh regime but not small enough for the more intense (dipolar type) plasmonic resonances to be present, the grid casts less shadow than the corresponding to the geometrical area covered. It can be said that the contacts become partially invisible. On a first introductory part, the influence of the grid on the cell series resistance related losses is presented. Based on the different weight of the parameters analyzed, the reduction of the finger spacing is chosen as the best alternative for efficiency improvement. In order not to affect other cell performance variables, the finger width has to be accordingly reduced keeping the shadowing factor of the state-of-the-art cells unchanged. Calculations made for an ideal case show that for grids made of 400-600 nm wide lines distributed with 10-20 μm period, the absolute efficiency gain can reach the 4%. There are other electrical effects that point to that width range as optimal...
Optoelectronic devices such as solar cells, flat panes and LEDs need electrical contacts on the front surface through which light enters or leaves. These contacts cause losses due to light absorption and reflection (shadowing) and electrical resistance. To a first approximation both losses are opposed in the sense that what improves shadowing worsens resistance and viceversa. This has been understood as an unavoidable compromise that limits the final energy conversion efficiency: reducing electrical losses necessarily means increasing optical shadowing losses. This thesis has dealt with the overcoming of this limitation through the nanostructuration of the font contact grid, with special attention to the case of concentrating photovoltaics (CPV). The objective is to simultaneously reduce grid related shadowing and series resistance losses. Based on theory, computer simulations and experiments we have found that for small grid-finger dimensions, on the onset of the Rayleigh regime but not small enough for the more intense (dipolar type) plasmonic resonances to be present, the grid casts less shadow than the corresponding to the geometrical area covered. It can be said that the contacts become partially invisible. On a first introductory part, the influence of the grid on the cell series resistance related losses is presented. Based on the different weight of the parameters analyzed, the reduction of the finger spacing is chosen as the best alternative for efficiency improvement. In order not to affect other cell performance variables, the finger width has to be accordingly reduced keeping the shadowing factor of the state-of-the-art cells unchanged. Calculations made for an ideal case show that for grids made of 400-600 nm wide lines distributed with 10-20 μm period, the absolute efficiency gain can reach the 4%. There are other electrical effects that point to that width range as optimal...
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Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, Departamento de Física de Materiales, leída el 05/02/2016