Electrodeposition of Tunable Zinc Oxide Nanomaterials for Optical Applications

Abstract

<p>Renewable energy technologies and the development of cleaner and more environmentally friendly power have been at the forefront of research for the past few decades. Photovoltaic systems – systems that convert photon energy to electrical energy – are at the center of these research efforts. Decreasing the cost of energy production, through increasing the power conversion efficiency or decreasing the device cost, is a key factor in widespread use of these energy production systems. To increase the energy conversion efficiency, ideally, all useful photons should be absorbed by the solar cell; however, due to the large discontinuity in the refractive index at the solar cell/air interface, a large fraction of incidence light is lost due to reflection (30% loss in crystalline silicon cells). The currently used single and double layer anti-reflection coatings reduce the reflection losses, but their optimal performance is limited to a narrow range of wavelengths and angles of incidence. Moth-eye anti-reflection coatings are composed of patterned single layer films having a gradual decrease in refractive index from the solar cell surface to air. This study is focused on developing an inexpensive method for direct deposition of patterned films – in the form of moth-eye anti-reflection coatings – on solar cell surface.</p> <p>In this research, the creation of moth-eye anti-reflection coatings has been attempted through the process of electrodeposition. ZnO was chosen for the thin film material, and the ability to develop the required moth-eye structure by changing the electrodeposition parameters including temperature, applied potential, type and concentration of solution-borne species, and type of substrate was investigated. Using this method, pyramidal and hemispherical structures with a 100-200 nm diameter and 100-200 nm height were created directly on ITO substrates. Similar structures were also developed on silicon substrates. The anti-reflection properties of ZnO-coated silicon substrates were investigated by comparing their broadband and broad angle reflection-mode UV-VIS spectrum with uncoated silicon. The optimized ZnO-coated silicon substrate showed a reflectance of at most 20% for wavelengths between 400-1500 nm at angles of incidence less than 50^O.</p>