Solar cell research is becoming increasingly important as photovoltaic power is forecast as a growth leader among other alternative energy sources for the next decades. Thin-film solar cells offer the advantages of low cost, light weight, and mechanical flexibility compared to bulk silicon devices used so far.
The goal of this proposal is the development of thin-film solar cells with increased efficiency and reduced cost. In order to increase the efficiency of the devices, we propose to partially cover the top surface of the active layer with a dense regular array of mono-dispersed metallic nanoparticles (e.g., Au, Ag, or Al), which will provide efficient coupling and trapping of light inside the thin active layer via its broad-angle scattering, thereby offering increased light absorption without compromising charge collection. Our objective is to implement this geometry with two different kinds of active layers: organic heterojunction films composed of polymer:fullerene interpenetrating networks and amorphous hydrogenated Si films. The power conversion efficiency of organic solar cells (today: 8.2%) is still below that of inorganic devices, however their remarkable mechanical and optical properties make them ideal for applications in consumer flexible electronics and smart fabrics. Amorphous hydrogenated Si (Si:H) thin-film solar cells offer higher power conversion efficiencies, up to 12%, and use the advantage of the existing infrastructure of Si industry. Both systems are expected to contribute to solar power generation in the future. For reduced cost, we plan to replace ITO, which usually serves as the transparent electrode of the device, by ZnO, which does not contain the expensive and scarce element In. Once we optimize the design and relevant parameters of such a single, model plasmon-enhanced solar cell, we will proceed to using laser scribing for the electrical connections, in view of building monolithic solar cell arrays in the future.
To achieve the goal of the proposal, ZnO-covered glass will be prepared by pulsed laser deposition. Dense arrays of monodispersed Au, Ag, or Al nanoparticles will be deposited on the ZnO electrode for efficient light absorption inside the photo-active amorphous Si:H or photopolymer layers, using femtosecond laser-induced forward transfer or thin-film spinodal decomposition techniques. Organic and amorphous Si:H layers will be prepared by spin coating and pulsed laser deposition, respectively. The metallic back electrode of the device, acting as total mirror, will be functionalized in a similar way as the front electrode with metal nanoclusters, for light scattering into the active medium. After optimizing the efficiency of the device, we will reduce the cost further by employing sol-gel methods for the ZnO electrode deposition and, potentially, thin-film spinodal decomposition for nanoparticle array deposition. Finally, we will employ laser scribing to collect experimental data for the electrical interconnections between cells connected in series for future monolithic arrays.