Plasmonic Photocurrent Enhancement in Silicon-on-Insulator Devices Due to Colloidal Silver Nanoparticles
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Plasmonic Photocurrent Enhancement in Silicon-on-Insulator Devices Due to Colloidal Silver Nanoparticles Birol Ozturk1, Eric A. Schiff1, Hui Zhao1, Fehmi Damkaci2, Baojie Yan3, Jeff Yang3 and Subhendu Guha3 1
Department of Physics, Syracuse University, Syracuse, New York 13244, U.S.A. Department of Chemistry, SUNY Oswego, Oswego, New York 13126, U.S.A. 3 United Solar Ovonic LLC, Troy, Michigan 48084, U.S.A. 2
ABSTRACT A layer of silver nanoparticles created by thermal annealing of evaporated silver films can increase the photocurrents in silicon-on-insulator (SOI) devices by fivefold or more, but significant enhancements have been restricted to wavelengths greater than 800 nm. Here we report a significant enhancement of photoconductance at shorter wavelengths (500-750 nm) by using a monolayer of silver nanoparticles transferred from a colloidal suspension. Photocurrents on SOI increased in the 500-750 nm spectral range with the addition of silver nanoparticles, with enhancements more than two times; enhancements at longer wavelengths were small, in contrast to results with annealed silver films. We prepared similar colloidal silver nanoparticle monolayers layers on nanocrystalline silicon solar cells with conducting oxide top layers. There is an overall decrease in the quantum efficiency of these cells with the deposition of silver nanoparticles. We attribute these effects to the substantial substrate-mediated changes in the localized surface plasmon resonance frequencies of the differing nanoparticle configurations. INTRODUCTION Metallic nanostructures are emerging as a new technology for efficiency enhancement in thin-film solar cells. Many researchers in the field are motivated by two separate studies demonstrating substantial enhancement in photocurrents of silicon-oninsulator (SOI) photodetectors with the deposition of silver nanoparticles [1,2]. These nanoparticles were fabricated by thermal annealing of evaporated silver films. Furthermore, a slight reduction was observed in the photocurrent spectra of the SOI devices for wavelengths less than 670 nm [2,3]. This loss was attributed to the absorption of the incident field by smaller diameter silver nanoparticles [3]. As an alternative method to annealed silver films (A-SFs), colloidal nanoparticles possess several advantageous properties such as facile integration to industrial fabrication and better size control. It was previously shown that the deposition of colloidal gold nanoparticles on a thin-film amorphous silicon solar cell does not improve photocurrents substantially [4]. Silver nanoparticles have higher radiative efficiencies compared to gold counterparts [1], but their colloidal form has not (to the best of our knowledge) been previously employed in plasmonic enhancement studies of SOI photodetectors and thinfilm silicon solar cells. In this paper we present our results on the photocurrent enhancement of SOI photodetectors at shorter wavelengths (500-750 nm) after the deposition of colloidal
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