Organic solar cell (OSC) is a highly promising research field with a strong potential to realize low cost solar cells with flexibility and light weight. Although OSC power conversion efficiency (PCE) exceeding 9% has been achieved recently, great efforts are still needed to strive a PCE over 10% making OSC ready for commercialization. Besides the demand of high PCE, other considerations, such as easy solution process, stability and large area processing, are also required for mass production in future. With the understanding of key technical issues that still challenge OSC towards widely spread applications, our worksarefocusingon1) applying the solution processed inorganic materials to ameliorate the intrinsic drawback in OSCs; and 2)proposing novel and simple solution process to improve electrical properties of OSCs by controlling the film quality thus the electrical properties during the film formation process. Detailed work is listed below: 1. Incorporating of metal nanoparticles (NPs) for improving OSC efficiency Metal NPs are selected as the candidate for improving OSC efficiency through their unique optical and electrical properties. Our results show that (1a) When meal NPs are incorporated in the hole transport layer (HTL) poly-(3, 4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), the PCE of OSCs are improved due to enhanced conductivity and rough surface. (1b) When metal NPs are embedded in the active layer, OSC performance can be further enhanced due to improvement in light absorption and electrical properties. When we incorporate Au NPs in all organic layers of OSCs, accumulation improvements in OSC performances can be achieved. (1c) When metal NPs are incorporated in electron transport layer of TiO2, the experimental results show that the enhanced charge extraction under solar illumination can be attributing to the UV-excited electrons transfer from TiO2electron transport layer and storage by Au NPs. 2. Solution processed metal oxide thin film for high efficient hole transporting layer (HTL) The solution-processed transition metal oxides (TMOs) have attracted great attention due to their superior air-stability properties and universal energy level alignment with organic materials. In this thesis, we propose a one-step method to synthesize low-temperature solution-processed TMOs such as molybdenum oxide and vanadium oxide, with good film quality, desirable electrical properties, and improved device stability, for HTLs applications. 3. Self-assemble metal oxide for high efficient electron transporting layer (ETL) We propose a self-assemble and solution-processed method in fabricating ETLs composed of TiO2 NPs that can simultaneously achieve good film uniformity and homogeneity, and electron transport properties. We believe this new method will be capable for large-area applications in future. 4. Vertical morphology control for active layer. Besides carrier transport layers, the morphology of the active layer will significantly affect its electrical and optical properties and thus device performance. We propose up-side-down method to modify the nano-morphology blend along vertical direction, which is beneficial to vertical charge transport and thus producing higher OSC performances. The film-growth dynamics of polymer blends is studied, which has been neglected in most study of OSC morphology by others. / published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

Dye sensitized solar cells (DSSCs) have received extensive attention among solar cells in recent years as the production cost is comparatively low and photovoltaic performance is good. Apart from TiO2, SnO2-based DSSCs are of great interest since SnO2 has a wide band gap and high mobility. Though the conversion efficiency of SnO2-based DSSCs is still not comparable to TiO2-based DSSCs, there is room for improvement to fabricate an efficient device. In this study, different commercial SnO2 nanoparticles have been compared. The number of SnO2 layers and paste formulation have been optimized. The effects of TiCl4 and TTIP treatments have been investigated. In order to further optimize the performance of SnO2-based DSSCs, different strategies have been adopted to increase dye loading, facilitate electron transport and enhance photon absorption. Different dopants (Zn, Mg and Ag) have been introduced to SnO2 pastes. It is found that cells with Zn dopants perform the best with increased dye uptake. SnO2 nanorods have been synthesized and mixed with SnO2 nanoparticles. More nanorods result in faster electron transport and hence increase the conversion efficiency. In addition, different gold nanostructures (nanostars, nanorods and nanocubic Au) have been synthesized and incorporated into SnO2 photoanodes to study the plasmonic effects. It can be observed that nanocubic Au demonstrates the largest improvement in conversion efficiency. The obtained results will be discussed in detail. / published_or_final_version / Physics / Master / Master of Philosophy

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published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy

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