The effect of metal nano-composites on the performance of thin film organic solar cells.

Abstract

This thesis examines the role of plasmonic nano-particles in the fabrication of thin film organic solar cells (OSCs). Organic solar cells are made up of conducting polymers blend that are formed as ultrathin layers (a few tens of nanometers thick) on various types of substrates. These conducting polymers, unlike their inorganic counterparts, have high optical absorption coefficients, allowing for the fabrication of ultra-thin solar cells (100–200 nm) in thickness. Moreover, they offer several advantages over other solar cell technologies in terms; mechanical flexibility, cheap device processing using roll-to-roll printing methods and etc. Organic photovoltaics (OPV) is a sector that has been steadily increasing over the last past two decades, with a justifiable power conversion efficiency (PCE) of 17 % to date. However, organic photovoltaic cells whose photo-active material is sandwiched between two differing work functions, are exhibiting relatively low PCE due to poor charge carrier generation and charge transport processes. Several factors can be considered in improving the overall performance of organic solar cells. These include enhancing photon harvesting ability of the absorber layer, reducing energy losses through recombination processes and so on. In recent years, significant advancements in OSCs have been made through the use of metal nano-composites or nano-particles in the solar absorber and transport buffer layers. It is to be noted that the shape and size of the metal nano-composite play an important role to achieve the required impact in OSCs. This investigation emphasizes on the use of tri-metallic nano-composites to assist in improving optical absorption, free charge carrier generation and charge transport processes. The goal of the research was to improve the power conversion efficiency of thin-film organic solar cells by using a trimetal nano-composite in the active layer (P3HT:PCBM). Based on Ce:Co:Ca nano-composites (NCs), the best device enhancements of PCE value of 5.3 % were discovered. The PCE of Ag:Zn:Ni NCs increased by up to 84 % from an initial value of 1.8 %, while Ag:Fe:Ni NCs improved by up to 3.83 % from an initial value of 2.70 %. Metal NCs feature local surface plasmon resonance (LSPR), which improves the power conversion efficiency of solution produced thin film organic solar cells. Because of the interaction with illumination, LSPR creates strong electromagnetic fields in the region of the particles on the one hand, and scattering effects in solar cell devices. However, high concentration of nanoparticles is found to be counter productive in the performance of OSC.