Synthesis and Characterization of Hole-Transporting and Electroluminescent Polymers

This thesis describes research on synthesis and characterization of electroluminescent and hole-transporting polymers for applications in organic light-emitting diodes (OLEDs). The first part of the project focuses on the synthesis of derivatives of the electroluminescent polymer poly(para-phenylenevinylene) (PPV) using ring-opening metathesis polymerization (ROMP) of substituted barrelenes. Barrelenes (a certain kind of bicyclic olefins) have been prepared through multi-step synthetic procedures, and the existing synthetic route was extended to barrelenes without electron-withdrawing groups. ROMP of barrelenes was explored because this polymerization can be living, which allows the preparation of well-defined polymeric products. A new version of a soluble PPV derivative was prepared via this route. The second part of the project focuses on hole-transporting (HT) polymers. A range of HT polymers were prepared via ROMP and anionic polymerization to explore the influence of different hole mobility and different ionization potential on the performance of a two-layer OLED. OLED devices were fabricated using spin-casting and vacuum vapor deposition, and were characterized in terms of current-voltage behavior and light output. A photo-crosslinkable hole transport layer was demonstrated. The HT polymers have been found to yield improved OLEDs by comparison to analogous small-molecule materials due to better film coverage and better film morphology. The device performance has been found to improve with increasing ionization potential of the hole transport polymer. An optimized device was fabricated, which showed 20 Lm/W efficiency. The best HT polymer was modified further to improve the operational stability of the device by improving the interfacial contact to the anode. A better adhesion to the conducting glass was achieved by preparing trimethoxysilane-containing copolymers via radical polymerization, and developing a procedure to cross-link these copolymers to the anode surface. The appendix describes a project unrelated to the general topic of materials for OLEDs. It presents a study on four chiral molybdenum-based ROMP-initiators with regard to their ability to yield highly stereoregular polymers.</p

Synthesis of high-T_g hole-transporting polymers with different redox potentials and their performance in organic two-layer LEDs

Organic hole transport materials are used in organic LEDs, where they substantially improve device performance if placed as a hole transport layer (HTL) between the anode and the electroluminescent layer (EL). Soluble polymeric hole transport materials with high glass transition temperatures are of particular interest, because they allow for efficient device fabrication through spin casting of the HTL, and high glass transition temperatures have been found to improve thermal and long-term stability of the device. The redox potential of the hole transport material determines the facility of charge injection at the anode/HTL and the HTL/EL interfaces, thus affecting the overall device efficiency. We have synthesized a series of soluble hole-transporting polymers with glass transition temperatures in the range of 130 degrees C to 150 degrees C. The synthetic method allows facile substitution of the hole transport functionality with electron-withdrawing and electron-donating groups, which permits tuning of the redox potential of the polymer. These polymers have been used as HTL in tow-layer devices ITO/HTL/Alq/Mg. The maximum external quantum efficiency increase, if the redox potential is changed to facilitate reduction of the hole transport material at the HTL/EL interface. Electron-deficient derivatives show higher external quantum efficiencies. The device stability, however, follows the opposite trend

Synthesis of Substituted Bicyclo[2.2.2]octatrienes

An efficient route to bicyclo[2.2.2]octatriene, barrelene, and substituted versions of this molecule has been developed starting from the benzene equivalent cis-3,5-cyclohexadiene-1,2-diol. Following the Diels−Alder reaction of this molecule with an activated acetylene, conversion of the diol to the final olefin was accomplished through formation of a thiocarbonate intermediate and subsequent reaction with 1,3-dimethyl-2-phenyl-1,3,2-diazaphospholidine (DPD). The synthesis developed allows a variety of barrelenes to be prepared in as few as three steps from commercially available starting materials

Synthesis of Substituted Bicyclo[2.2.2]octatrienes

An efficient route to bicyclo[2.2.2]octatriene, barrelene, and substituted versions of this molecule has been developed starting from the benzene equivalent cis-3,5-cyclohexadiene-1,2-diol. Following the Diels−Alder reaction of this molecule with an activated acetylene, conversion of the diol to the final olefin was accomplished through formation of a thiocarbonate intermediate and subsequent reaction with 1,3-dimethyl-2-phenyl-1,3,2-diazaphospholidine (DPD). The synthesis developed allows a variety of barrelenes to be prepared in as few as three steps from commercially available starting materials

Synthesis of high-T_g hole-transporting polymers with different redox potentials and their performance in organic two-layer LEDs

Organic hole transport materials are used in organic LEDs, where they substantially improve device performance if placed as a hole transport layer (HTL) between the anode and the electroluminescent layer (EL). Soluble polymeric hole transport materials with high glass transition temperatures are of particular interest, because they allow for efficient device fabrication through spin casting of the HTL, and high glass transition temperatures have been found to improve thermal and long-term stability of the device. The redox potential of the hole transport material determines the facility of charge injection at the anode/HTL and the HTL/EL interfaces, thus affecting the overall device efficiency. We have synthesized a series of soluble hole-transporting polymers with glass transition temperatures in the range of 130 degrees C to 150 degrees C. The synthetic method allows facile substitution of the hole transport functionality with electron-withdrawing and electron-donating groups, which permits tuning of the redox potential of the polymer. These polymers have been used as HTL in tow-layer devices ITO/HTL/Alq/Mg. The maximum external quantum efficiency increase, if the redox potential is changed to facilitate reduction of the hole transport material at the HTL/EL interface. Electron-deficient derivatives show higher external quantum efficiencies. The device stability, however, follows the opposite trend

CO2-Reduktion in der Zement- und Kalkindustrie – Wie vermeidet man unvermeidbare Emissionen?

CO2 reduction in the cement and lime industry - How to avoid unavoidable emissions? CO2 emissions of the cement and lime industry are an especially challenging topic for the climate policy debates, because the process emissions from these industries are unavoidable. To reach the goal of climate neutrality, it is necessary to minimize the consumption of cement clinker and other products made from lime stone, as well as to utilize Carbon Capture and Storage (CCS) to capture and permanently store CO2. In highly developed industrial countries with a projected reduction in population, such as Germany, the demand for cement could drop to half of current consumption. Worldwide, however, a constant demand is expected despite ambitious reduction measures. Therefore, implementation of CCS is key to achieving a climate neutral cement and lime industry. Technical questions are largely solved and main barriers to a fast and wide-spread implementation are mainly a lack of regulatory frame work and a low public acceptance of the technology

Hole Transport Polymers with Improved Interfacial Contact to the Anode Material

New hole transport polymers have been prepared through copolymerization of a fluorinated triphenyl diamine derivative and trimethoxyvinylsilane. The modification with trimethoxysilane groups has resulted in materials which can be cross-linked through hydrolysis and are capable of forming covalent chemical bonds to oxidic surfaces. Organic light-emitting diodes containing these polymers show decreased operating voltages and enhanced operational stability due to improved interfacial contact between the hole transport layer and the anode

Organic Two-Layer Light-Emitting Diodes Based on High-T_g Hole-Transporting Polymers with Different Redox Potentials

A series of soluble arylamine-based hole-transporting polymers with glass transition temperatures in the range of 130−150 °C have been synthesized. The synthetic methodology allows facile substitution of the aryl groups on the amine with electron-withdrawing and electron-donating moieties, which permits tuning of the redox potential of the polymer. These polymers have been used as hole-transport layers (HTLs) in two-layer light-emitting diodes ITO/HTL/Alq/Mg [ITO = indium tin oxide, Alq = tris(8-quinolinato)aluminum]. The maximum external quantum efficiency of the device increases if the redox potential of the HTL is increased to facilitate reduction of the positive charge carriers at the HTL/Alq interface. A fluorinated hole-transport polymer with a relatively large redox potential (390 mV vs ferrocenium/ferrocene) yielded the device with the highest external quantum efficiency of 1.25% photons/e-. The device stability, however, follows the opposite trend. The device with the most electron-rich HTL exhibited the best performance after prolonged usage

Organic Two-Layer Light-Emitting Diodes Based on High-T_g Hole-Transporting Polymers with Different Redox Potentials

A series of soluble arylamine-based hole-transporting polymers with glass transition temperatures in the range of 130−150 °C have been synthesized. The synthetic methodology allows facile substitution of the aryl groups on the amine with electron-withdrawing and electron-donating moieties, which permits tuning of the redox potential of the polymer. These polymers have been used as hole-transport layers (HTLs) in two-layer light-emitting diodes ITO/HTL/Alq/Mg [ITO = indium tin oxide, Alq = tris(8-quinolinato)aluminum]. The maximum external quantum efficiency of the device increases if the redox potential of the HTL is increased to facilitate reduction of the positive charge carriers at the HTL/Alq interface. A fluorinated hole-transport polymer with a relatively large redox potential (390 mV vs ferrocenium/ferrocene) yielded the device with the highest external quantum efficiency of 1.25% photons/e-. The device stability, however, follows the opposite trend. The device with the most electron-rich HTL exhibited the best performance after prolonged usage