| Having pronounced advantages such as low cost,low energy consumption and capability of mass manufacturing under conventional environment,printing technology has found more and more applications in electronic devices and the related products in recent years.Printed organic light-emitting diodes?OLEDs?,organic photovoltaic cells?OPVs?,organic thin-film field-effect transistors?OFETs?have already become the research hotspots.Solution processability of organic semiconductor materials is recognized as one of the key factors in molecular material design.Compared with materials of small molecules,organic conjugated polymers are considered to be the most promising semiconductor materials for printed electronics not only due to their superior solution processability,but also the excellent film forming properties.Out of the huge varieties of conjugated polymers,the D-A type is being focused on because of its strong polarizing and electron-transferring effects within its mainchains which can drive effectively the mainchains to stack orderly in film,reducing the distance between the stacked polymer layers and ultimately leading to good electronic properties.Most of the studies for high-performance polymer semiconductor materials have been concentrated on the conjugated mainchains,but rarely on sidechains.It is revealed by recent studies that sidechains in conjugated polymers do not only enhance solubility of the polymer and therefore,improve its solution processability,but also influence and even control its spatial stacking state,film forming performance and film quality,and consequently,affect semiconductor and device properties of the polymer.The main work of this thesis is to design and synthesize the NDI-based electron transport type D-A conjugated polymers with fluorine-terminated branched alkyl sidechains and the DPP-based hole transport type D-A conjugated polymers with fluorine-and siloxane-terminated branched alkyl sidechains,respectively,and to study their photophysical,electrochemical and solution processing characteristics.Semiconductor properties of the obtained polymers are characterized through the assessment of the field effect transistors prepared using the obtained polymers.It is hoped that this work can provide useful exploring experiences for the development of printable semiconductor materials.The main works and results are summarized as follows:1.Naphthalenediimide?NDI?-based D-A type conjugated polymers T1-PC8NDIBT and T3-PC8NDIBT with fluorine-terminated branched alkyl side chains are synthesized,and the branching points of the side chains of T3-PC8NDIBT are farther to the mainchain than those of T1-PC8NDIBT.Experimental results indicated that the introduction of the fluorine-terminated sidechains facilitates the formation of closely packed film structures,thereby blocking the diffusion of water and oxygen into the semiconductor film and promoting the stability of the polymers in ambient air.Moreover,due to the interaction between the fluorine-terminated sidechains,interaction of the polymers in film state was enhanced.This facilitated charge transport in the polymers.Electron mobility of the polymer with fluorine-terminated sidechains was 6.0×10-1cm2V-1s-1 or three times higher than that of the cooresponding non-fluoro polymer.The farther the branching point of the side chain to the conjugated mainchain,the more planarity of the conjugated mainchain would be strengthened because of the reduced steric hindrance of the branched sidechains.And T3-PC8NDIBT-1 of smaller molecular weights exhibited the similar level of electron mobility of6.0×10-1cm2V-1s-11 as polymer T1-PC8NDIBT.Due to the expanded conjugated structure,T3-PC8NDIBT-2 of larger molecular weights was of deteriorated solubility and the polymer was prone to precipitate from its solution and the resulted film was of poor continuity.2.Two new series of D-A type diketopyrrolopyrrole?DPP?-based conjugated polymers PCDPPAr-F7and PCDPPAr-F9 with fluorine-terminated branched alkyl side chains were synthesized and their semiconductor properties were studied.The results showed that as the length of the fluorine-terminated sidechain increases,the degree of polymerization and consequently molecular weight of the polymers decrease due to the enhanced interaction between the fluoro-sidechains.Despite of different lengths of the alkyl sidechains,these two types of polymers exhibited almost the same electronic absorption peaks of intramolecular charge transfer and similar structure of energy levels,indicating that the sidechain has less effect on the energy-level structure of the conjugated mainchain.Different donor moieties,however,significantly affected the photophysical and electrochemical properties of the polymers.Due to the interaction between the fluoro-sidechains,PCDPPAr-F9 of longer fluoro-sidechains was found of lower solubilities as compared with PCDPPAr-F7.Intermolecular interactions between the conjugated polymer mainchain are hindered by the branched sidechains of larger steric hindrance,leading to random stacking of the conjugated mainchain in film and consequently,lower charge mobilities.The hole mobility of PC10DPPBT-F7 was found as low as 8.2×10-3cm2V-1s-1.3.Two new series of D-A type diketopyrrolopyrrole?DPP?-based conjugated polymers PC5DPPSe-Si and PC9DPPSe-Si with siloxane-terminated branched alkyl sidechains were synthesized and their semiconductor properties were studied.The results showed that the introduction of siloxane-terminated sidechains greatly improved the solubility of the polymers.Polymers with siloxane-terminated branched alkyl sidechains was found of higher solubilities and film quality as compared with liner sidechains polymers,meanwhile,the molecular weight of polymer with siloxane-terminated sidechains also increased.The spatial stacking state and film morphology of the polymers backbone were changed by the branched sidechains of larger steric hindrance,leading to random stacking of the conjugated mainchain in film and consequently,lower charge mobilities.The hole mobility of PC5DPPSe-Si and PC9DPPSe-Si were found as low as 5.6×10-3cm2V-1s-1 and 6.1×10-3cm2V-1s-1 respectively.However,the excellent solubility,allow the polymers can be fabricated using non-chlorinated solvents.At the same time,they can be prepared as organic electronic inks,and promote the forming of excellent film properties.4.Diketopyrrolopyrrole?DPP?-based D-A type conjugated polymer PDPPF-BT-Si with fluorine-and siloxane-terminated branched alkyl sidechains was synthesized,and its semiconductor properties were studied.The solubility of DPP-based polymer modified by the fluorine-terminated sidechain was improved by the good solubility of the siloxane-terminated sidechain.The results showed that the obtained polymer PPPPF-BT-Si has good solubility in general solvent,which is an important factor for the preparation of electronic ink,and the quality of the film is also greatly improved.The hole mobility of the devices fabricated by dichlorobenzene and low boiling chloroform solution is 6.5×10-3cm2V-1s-11 and 3.0×10-3cm2V-1s-1 respectively.That is a great progress compared to the polymer PCDPPAr-F9,which has no measured properties due to the poor processability of the polymer and the poor continuity of resulted film. |
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