The development and applications of metallic nanomaterials-based transparent electrodes on organic thin film solar cells
Date Issued
2015
Date
2015
Author(s)
Xu, Wei-Feng
Abstract
In this dissertation, we propose two kinds of transparent conductive electrodes based on metallic nanomaterials, such as metal thin films and nanowires, to efficiently improve the power conversion efficiency of organic soar cells with indium-tin-oxide-free (ITO) window electrodes by the synergetic effect of light scattering and plasmon-enhanced absorption. We also integrate a light-reflective back electrode featuring a corrugated metal surface with a multilayer-based light-incident front one. In multilayer-based metallic thin films, a transparent electrode consisting of nanoporous silver thin film and molybdenum oxide was developed for transparent anode with advantages of low cost, large-area processing and room-temperature fabrication. High density nanoporous silver film was fabricated by controlling thickness and deposition rate during thermal evaporation. With silver thickness of 10 nm and 5 Å s-1 deposition rate, the MoOx/nanoporous Ag/MoOx multilayer structure achieved ~ 9 Ω sq-1 sheet resistance and ~70% transparency. Compared to the ITO anode, the nanoporous anode/SubPc/C60/BCP/Al photovoltaic device has an enhanced surface-plasmon absorption and a higher fill factor. Although its transparency is lower than ITO, the nanoporous anode achieved 3.45% power conversion efficiency, comparable to ITO-based devices. In metal nanowires, solution-processed transparent electrodes made from silver-nanowires and peroxo-polytitanic (PPT) acid gel were developed for enhancing efficiency of organic solar cells. The electronic and optical properties of multilayer silver nanowires were significantly improved through the interconnection layers of amorphous titanium oxide (TiOx) from PPT acid gel. The AgNW-TiOx composite film showed averaged 92.14% optical transmittance with only 16.01 Ω sq-1 sheet resistance. Combining the transparent electrodes with poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PC61BM) blend, the efficiency of organic solar cells was 1.45 times of devices using ITO electrode. Optical simulations verified that the improvement was attributed to the enhanced near-field absorption and substantial scattering of incident light resulted from the random nature of the AgNW-TiOx core-shell nanostructure. In plasmonic-assisted nanostructured reflective electrodes, nanostructured back reflective electrode with nanobowl-shaped 2D nanohole arrays made from polystyrene (PS) nanosphere template was developed for enhancing efficiency of top-illuminated organic solar cells with MoOx (10 nm)/Ag (10 nm)/MoOx (25 nm) stacks as transparent electrode. The high-performance top electrode with a transmittance of 88.05% at 550 nm and a sheet resistance of 5.93 Ω sq-1 reached an extremely high figure of merit (
Subjects
Transparent electrodes
Organic photovoltaic cell
Metal thin films
Silver nanowires
Surface plasmon resonance
SDGs
Type
thesis