| Summary: | 博士 === 國立臺灣大學 === 材料科學與工程學研究所 === 101 === Polymer solar cell has attracted considerable attentions for tackling the energy problem owing to the advantages of solution process, flexibility, light weight, low cost, semi-transparency, etc. Improving power conversion efficiency (PCE) and device stability are the general goals for competing with fossil energy source and other photovoltaic (PV) technologies. In order to achieve the goals, the present research focuses on the topics of control and quantitative characterization of three dimensional nanostructures in polymer/nanoparticle bulk heterojunction (BHJ) solar cells, development of high stability polymer/inorganic hybrid BHJ solar cells, synthesis and development of novel low band gap inorganic nanocrystals, and investigations of tandem device structure.
Various processing strategies have been developed for improving PCE by controlling the 3-D nanostructures of BHJ. However, how the BHJ nanomorphology is tailored and the quantitative correlations to the enhanced PCEs are still limited. We aim to establish a quantitative evaluating methodology with associated fundamental knowledge of BHJ nanostructures. We developed an improved simultaneous grazing incidence wide/small angle X-ray scattering (GIWAXS/GISAXS) analysis technique. This method has been applied to resolve the structural evolutions of self-organized P3HT/PC61BM blends tuned by thermal annealing, solvent-vapor annealing, incorporation of inorganic nanoparticles (INPs) respectively and PCPDTBT/PC71BM blends tuned by solvent additives. We present quantitative studies of the BHJ nanostructures and an evaluating methodology which is helpful for further improving solar cell performance and associated processing design and materials synthesis.
The fullerene based solar cell has the disadvantages of low physical and thermal stability. In order to improve the device stability, the P3HT/TiO2 hybrids are alternatively employed as the BHJ layer that is implemented in inverted device architecture. An all solution processed and air-stable P3HT/TiO2 hybrid inverted hybrid solar cell is successfully developed, showing PCE of 1.2% and significant stability in ambient condition without encapsulation (less than 10% loss over 1000 hours). Furthermore, for addressing the issue of no absorption of TiO2 nanocrystals in visible and near infrared regions, we tried to develop copper zinc tin sulfide (CZTS) nanocrystals with low bandgap. We developed a facile one-pot heat up process to prepare the CZTS nanocrystal suspension which is potential for practical photovoltaic applications.
The tandem structure is promising for further improving the device performance overcoming the trade-off between output current and voltage in single junction devices. Herein the processing and device physics of tandem cells were systematically studied. We started with the fabrication of front sub-cell and addressing the problem of compatibility between inter-connection layer and BHJ layer. Additionally, composites of ZnO nanoparticles and PVP doped by CsCO3 was developed and applied in single and tandem solar cell to reduce the carrier recombination and increase the device performances. A 6.5% PCE of tandem cell was attained with little loss in output voltages from the sub-cells which indicated the successful fabrication of a tandem cell with efficient inter-connection layer. The established processing for tandem cell in the present work is extremely important for the following work aiming on higher power conversion efficiency. It is our hope that the results demonstrated in this dissertation will contribute to the advance of polymer based photovoltaics in the aspects of morphological investigation, materials development and device processing toward practically realizing the organic photovoltaic technology.
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