Donor-acceptor Conjugated Organic Materials for Bulk Heterojunction Solar Cells

• Main Authors: Jen-Hsien Huang, 黃任賢
• Other Authors: Kuo-Chuan Ho
• Format: Others
• Language: en_US
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/81936876756252249535

博士 === 臺灣大學 === 化學工程學研究所 === 98 === Over the past two decades, satisfying the world’s growing demand for energy is one of the most significant challenges facing society. Therefore, the development of solar energy is viewed as an ideal technology for power generation because it is clean and renewable. Although the photovoltaic (PV) technology platforms of silicon-based PV and thin-film PV are now undergoing a rapid expansion in production, the next generation PV—organic solar cells —could soon be playing a major role with the advantages of ultralow production costs, rugged and lightweight. The main purpose of this thesis is to fabricate PV cells via an all-solution-process and investigate the influences of materials and fabrication parameters on the device performance. In the first part of this thesis (Chapter 3 and 4), we prepared nanofiber shaped hole collection layer with highly porous structure by changing the structure of EDOT monomer. The highly porous hole collection layer prepared from electrochemical deposition can offer a great deal of interface between the hole collection layer and active layer leading to a more balanced charge mobility. The power efficiency of the device fabricated with porous hole collection layer can achieve 3.57% so far. Furthermore, we also enhance the conductivity of the hole collection layer (PEDOT) by treating the PEDOT with some polyalchols. From the results, it revealed that the conformation of PEDOT can be changed from coiled structure to linear structure after the treatment leading to a higher conductivity. The highly conductive PEDOT was also applied to fabricate PV cells and the power efficiency is about 4.30%. In the second part (Chapter 5), a novel solution-processed small molecule (DFTh-TP) for use in electron donor has been incorporated into the organic solar cells based on P3HT and PC[70]BM. The combination of DFTh-TP with P3HT and PC[70]BM allows not only a broad absorption but also tuning the inter energy level leading to a higher JSC and VOC. The best performing devices exhibited a power conversion efficiency of 4.50 %. The efficiency is increased of almost 15 % compared with the one without incorporating DFTh-TP. In the third part (Chapter 6), we performed a comprehensive analysis of the 2D nanoscale morphology related to the exciton lifetime by combining confocal optical microscopy with a fluorescence module. The results revealed that the film prepared through rapidly grown process leads to an extremely homogeneous blend. The homogeneous phase cannot offer a continuous pathway for charge transport leading to a serious recombination. In the case of slowly grown film, although not all of these pathways may have been ideal, due to the presence of some terminated channels, this system still offered several connected pathways, leading to an interdigitated nanostructure that was responsible for efficient charge transport and the superior value of JSC. This approach provides much fundamental information that is unavailable when using conventional microscopy techniques in the future. In the fourth part (Chapter7~9), we have fabricated organic photovoltaic devices with blends of F8T2 and fullerene as an electron donor and electron acceptor, respectively. A significant improvement of the photovoltaic efficiency was found in device by using PC[70]BM as active material with complementary spectra. Moreover, we also study the effects of nanomorphological chnages on polymer PV devices with blends of F8T2 and PC[60]BM. The morphological changes of blended films were observed upon thermal annealing temperature near and above glass transition temperature (130 oC). Such microstructural transformations resulted in modified charge transport pathways and therefore grately influenced the device performance. The highest PCE of 2.14 % with an VOC of 0.99 V and a JSC of 4.24 mA/cm2 was achieved by device annealing at 70 oC for 20 min. In the final part (Chapter 10), we modified the printing method by increasing the affinity of PDMS for organic solvent via non-destructive solvent treatment. This stamping method eliminates the necessity of any plasma treatment and any possible damages on the PDMS surface and would give full control over the chemical composition and film thickness of each layer. The multilayer polymer structure also demonstrated for photovoltaic applications.