Optical properties of ZnO-CdTe electrochemically prepared on a core-shell nanostructure (NS) were studied. Numerical simulations based on effective medium approximation give higher absorption than ZnO-CdS samples and a sensitive dependence on CdTe content. The absorption edges for deep black samples found by transmittance (T(λ)) and diffuse reflectance (Rdiff(λ)) measurements were at 1.33eV and 1.55eV, respectively. A split-off band edge was also found by Rdiff(λ) at ∼2.5eV. The red shift observed in T(λ), previously observed in ZnO-CdS, and may confirm the enhancement of sub-bandgap absorption due to the NS nature of samples.
RESUMENSe estudiaron las Propiedades Ópticas (PO) de Nanovarillas (NV) de ZnO sensibilizadas con diferentes semiconductores en nanoestructuras núcleo-corteza, comparándolas con las PO de NV de ZnO. Las medidas experimentales de Transmitancia y Reflectancia Difusa muestran un incremento en la absorción de luz en el espectro solar y la aparición de nuevos bordes de absorción (BA). Las medidas se compararon con simulaciones numéricas basadas en Aproximación de Medio Efectivo (Bruggeman). Las simulaciones corresponden con las medidas reproduciendo la dependencia con el contenido de sensibilizante. Para CdTe se observa un aumento de la absorción con la cantidad del sensibilizante, siendo los cambios mayores para iguales cambios en las fracciones de llenado respecto al CdS. Las mediciones experimentales muestran corrimientos en las posiciones de los BA entre 2.34 eV y 2.66 eV para CdS. Estos corrimientos no pueden explicarse sólo por cambios en el contenido de sensibilizante o por los efectos de confinamiento en las nanoestructuras. Similar es el comportamiento del BA de muestras sensibilizadas con CdTe que se ubica entre 1.31 eV y 1.36 eV, analizadas por Transmitancia, mientras que para las mismas muestras este BA se encuentra en 1.57 eV y 1.49 eV, respectivamente, según el método de Kubelka-Munk de la Reflectancia. Además se observa el BA de la banda split-off en 2.55 eV y 2.28 eV. Estos corrimientos pueden asociarse a un incremento de la absorción sub-bandgap debido al aumento del recorrido libre medio de la luz en la estructura.Palabras clave: Nanoestructuras, ZnO, Nanohilos, Celdas Solares ABSTRACTThe Optical Properties of ZnO Nanorods (NR) sensitized with different semiconductors in Core-Shell nanostructures were studied, comparing them with those of bare ZnO NR. Experimental measurements of Transmittance and Diffuse Reflectance show an increased light absorption at the solar spectrum and the appearances of new absorption edges (AE). The measurements are compared with numerical simulations based on Bruggeman Effective Medium Approximation. An increased absorption with the sensitizer content is observed. For similar changes in filling fractions, CdTe presents higher changes in absorption than CdS. Shifts in the AE are observed experimentally (e.g. between 2.34 eV and 2.66 eV for CdS). These shifts cannot be assigned to sensitizer content or confinement effects. A similar behaviour is observed for CdTe in which the AE measured by transmittance is between 1.31 eV and 1.36 eV, while the one obtained from Kubelka-Munk analysis of reflectance is, for the same samples, 1.57 eV and 1.49 eV, respectively. Moreover, the split-off AE is also observed at 2.55 eV and 2.28 eV. The observed large red-shifts could be associated with an enhancement of the subbandgap absorption due to an increase in the light free path at the core-shell nanostructure.PEREYRA, C.J.; FERRER, F.; GÓMEZ,C.; CAMPO, L.; MAROTTI, R.E.; MARTIN, F.; LEINEN, D.; BARRADO, J.R.; DALCHIE-LE, E.A. revista Matéria, v.20, n.3, pp. 747 -756, 2015. 748
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