High performance organic solar cells with interface engineering

Polymer solar cells are considered a promising candidate for renewable energy with low-cost and high volume production capability. The main focus of this dissertation is to investigate the several approaches for improving the efficiency of polymer solar cells. These approaches include understanding of the physics, operation mechanisms, materials and device engineering and optimization of fabrication processes.;A typical polymer solar cell has a sandwiched structure with anode, active material, and cathode. To improve device performances, it is often to introduce interfacial layers between the anode and cathode interfaces. These interfacial layers can be conductive polymers, metal oxides, and other nano-structure materials. In this thesis, we focus on a novel metaloxide derivative. Synthesizing metal oxides through the sol--gel process provides a convenient way of forming nanostructured wide band gap semiconductors. In this dissertation, a doped metal oxide functional interfacial layer is introduced for achieving high performance organic electronic devices. The role of dopants is found to modify the electronic property of the metal oxide. Polymer solar cells and polymer light emitting devices with this functional layer exhibited excellent characteristics. The improved device performance is attributed to an improved polymer/metal contact, more efficient electron extraction, and better hole blocking properties.;Another aspect of polymer solar cells is the potential to double the efficiency by using the tandem structure. Hence, the research on the understanding of tandem structure has become one of the frontiers in the field of organic/polymer photovoltaics. This dissertation discusses the role of the inter-connection layer in the tandem cell. We focus on the understanding and improvement of the interfaces within the interconnection layer, and its role for charge collection and recombination. Based on this understanding, high efficiency tandem cell with a power conversion efficiency close to 5.9% was demonstrated from recently reported low band gap polymer and poly(3-hexylthiophene) (P3HT) systems.;Finally, a functional metal oxide interlayer is employed in the low band gap polymer photovoltaic system for better performance of polymer solar cells. The improvement in device performance is mainly due to reduced electrode-exciton quenching and enhanced electron extraction from the active layer to the electrode.