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    Aggregation of Organic Semiconductors and Its Influence on Carrier Transport and Solar Cell Performance

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    Hanlin Hu - Dissertation - Final Draft.pdf
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    10.14Mb
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    Type
    Dissertation
    Authors
    Hu, Hanlin cc
    Advisors
    Amassian, Aram cc
    Committee members
    Alshareef, Husam N. cc
    McCulloch, Iain cc
    Michels, Jasper J.
    Program
    Material Science and Engineering
    KAUST Department
    Physical Science and Engineering (PSE) Division
    Date
    2017-08-28
    Permanent link to this record
    http://hdl.handle.net/10754/625509
    
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    Abstract
    Photovoltaic technology based on solution-processable organic solar cells (OSCs) provides a promising route towards a low-cost strategy to address the sharply increasing energy demands worldwide. However, up to date, the vast majority of solar cell reports have been based on spin-cast BHJ layers. Spin coating is not compatible with high speed and scalable coating processes, such as blade-coating and slot-die coating, which require the nanoscale morphology to be reproduced in scalable coating methods. And tolerance for thicker BHJ films would also facilitate high speed scalable coating. In the first part of this thesis, we investigate how pre-aggregating the conjugated polymer in solution impacts the charge transport in polymer films. We use P3HT in a wide range of molecular weights in different solvents of common use in organic electronics to investigate how they impact the aggregation behavior in the ink and in the solid state. By deliberately disentangling polymer chains via sonication of the solution in the presence of solvophobic driving forces, we show a remarkable ability to tune aggregation, which directly impacts charge transport, as measured in the context of field effect transistors. The second part of this thesis looks at the impact of the solution-coating method and the photovoltaic performance gap when applying modern BHJ inks developed for spin coating to scalable coating methods, namely blade coating. We ascribe this to significant differences in the drying kinetics between the processes. Emulating the drying kinetics of spin-coating was found to result in performance parity as well as morphological parity across several systems, resulting in demonstration of PTB7:PC71BM solar cells with efficiency of 9% and 6.5% PCEs on glass and flexible PET substrates, respectively. The last part of this thesis looks into going beyond performance parity by leveraging the differences of the scalable coating method to enable highly efficient thick solar cells which surpass the performance of spin-cast devices. High-speed wire-bar coating (up to 0.25 m/s) was used to produce OPV devices with power conversion efficiency (PCE) >10% and significantly outperforming devices prepared by spin-coating the BHJ layer for thicknesses >100 nm by maintaining a higher fill factor.
    Citation
    Hu, H. (2017). Aggregation of Organic Semiconductors and Its Influence on Carrier Transport and Solar Cell Performance. KAUST Research Repository. https://doi.org/10.25781/KAUST-QDI83
    DOI
    10.25781/KAUST-QDI83
    ae974a485f413a2113503eed53cd6c53
    10.25781/KAUST-QDI83
    Scopus Count
    Collections
    PhD Dissertations; Physical Science and Engineering (PSE) Division; Material Science and Engineering Program

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