Semiconducting polymers are promising materials for next-generation, flexible electronics devices. Over the last decades, various types of polymers have been developed and applied to devices such as light-emitting diodes (OLEDs), photovoltaics (OPVs), and field-effect transistors (OFETs). Conductivity is one of the most important parameters for the device performance since it directly affects charge carrier collection, injection, and transport. Besides, not only bulk conductivity but also interfacial energy barrier is critical for multilayer devices, especially an energy alignment of layers is essential to collect/inject charge carriers smoothly. Therefore reliable systems for both p- and n-type doping are sought after. Chemical doping (molecular doping) is a promising technique to achieve both, to enhance the conductivity in polymers and to shift energy levels by generating charge carriers (holes or electrons) in polymer films. The method enables to transport charge carriers in thin films or between neighboring layers effectively.
This thesis investigates the chemical doping from the nanostructure level, particularly two types of devices where doping plays a crucial role: 1) pressure sensor based on p-doped semiconducting polymer nanopillars, 2) novel n-type doping system for a technologically advantageous thick interlayer in organic solar cells.
In the first part, an application of nanostructured p-doped polymer was explored in a new type of device. While p-type doping is relatively common, especially for P3HT or PEDOT:PSS, in OPVs or OFETs, the potential of semiconducting polymer material, especially its mechanical flexibility and high electrical conductivity, is not fully utilized in these types of devices. Therefore new electronic device, a pressure sensor, is fabricated based on nanopillar structures made of p-doped P3HT by a templating method. The highly flexible and conductive nanostructure was obtained by combining templating and chemical doping. Through utilizing the buckling behavior of nanopillars, the pressure sensor was constructed and used for the detection of finger movement and touch sensing with a robotic gripper. Besides, the templating process can be tuned by annealing conditions, that enable adjusting the length of nanopillars and thus sensing properties. Finally, the sensing mechanism was investigated by finite element modeling and Euler buckling theory.
In the second part, n-type doping in novel polymers was investigated. Generally, n-type doping has relatively limited reports since the n-doped state of commonly used polymers is readily oxidized by oxygen or water in air. A newly synthesized series of naphthalene diimide (NDI)-based conjugated polyelectrolytes (CPEs) contains cations in side chains, which stabilize the generated charge carriers. The stability of conductivity, spectroscopic characteristics, morphology, and the application of CPEs to interlayers in polymer solar cells (PSCs) were investigated. The polymer film showed air-stable high conductivity by introducing self-compensation doping and anion doping methods. The LUMO level of CPEs has a strong correlation with the conductivity in air and long-term stability. Moreover, the work function of the ITO cathode can be shifted by CPEs and the chemical doping, enabling a highly conductive, thick cathode interlayer, applicable to scalable film deposition methods, e.g., the blade-coating method.
For the outlook, various new applications can be realized by combining these techniques and materials for p-/n-doping systems. This research expands the utilization of semiconducting polymer as a nano-structurable, flexible, highly conductive, and air-stable component for future flexible electronics devices.
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:76308 |
| Date | 15 October 2021 |
| Creators | Tsuda, Takuya |
| Contributors | Fery, Andreas, Zschech, Ehrenfried, Technische Universität Dresden |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
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