Please use this identifier to cite or link to this item:
In Situ Template Synthesis of Conjugated Polymer/Inorganic Oxide Nanohybrid System at Elevated Pressures: Study on Hybrid Morphology, Optoelectronic Properties and Application in Solar Cells
hybrid solar cells,P3HT,TiO2,ZnO nanoparticles,nanowires,
|Publication Year :||2016|
|Abstract:||有機/無機混成材料因其具有低成本、柔曲性、輕穎性以及便於量化製造的優點，因此是個極具前瞻性的研究主題。然而，要得到較好的功能特性，需仰賴較大的電荷傳導界面及建構良好的傳輸結構來達成，而這樣的控制技術至今仍然是一項待需克服的重要課題。在這本論文裡，我們開發了一項新穎的原位高壓水熱法來製備共軛高分子/無機奈米粒子之混成材料，且此材料具有自組裝成奈米線結構的特性。在第一部分的研究中，聚噻吩高分子(P3HT)和鈦前驅物先相互作用並共組裝成奈米線之結構，再經由水熱法將鈦前驅物直接在P3HT之奈米線上轉化成具結晶性之二氧化鈦(TiO2)奈米顆粒。P3HT奈米線在此混成系統中，除了當作電子提供者外，亦可做為一種模板來達到有效分散二氧化鈦奈米顆粒的目的。特別的是，相較於一般高結晶性二氧化鈦的製備需經過高達450 °C以上的高溫鍛燒，以此高壓水熱法(~7 bars)製備具高結晶度之銳鈦礦型TiO2的製備溫度則可以大幅降低至130 °C。因此，此方法提供了一種可以經由一個步驟的過程，就製備出同時含有高結晶度之P3HT和TiO2混成奈米線。這樣的結構大幅提升了此P3HT/TiO2混成系統中的電子傳輸界面以有效促成激質的分離(exciton dissociation)，而得以獲得較佳的元件表現。相較於非使用此原位合成法製備之奈米混成系統的元件效率而言(PCE: 0.03%)，經由原位高壓法製備之P3HT/TiO2混成元件則具有達0.14%的效率表現，表現出顯著之進步。
第二個部分中，則是以相似的原位高壓水熱法來製備製備P3HT/ZnO奈米粒子之混成材料，此混成材料具有長約500 nm以上，寬約24 nm左右的奈米線結構。P3HT分子鏈上的硫原子可作為一種固定座，用來與鋅前驅物形成錯合物(complex)，再經由高壓水熱法(~9 bars)將鋅前驅物直接在P3HT之奈米線上轉化成具結晶性之氧化鋅(ZnO)奈米顆粒。P3HT和ZnO的配位鍵結力可以帶來控制分散ZnO奈米顆粒的作用，以達到較佳的分散效果。經由此高壓水熱法，可在相對低溫的150 °C就合成出具有高結晶性的纖鋅礦型ZnO奈米顆粒;然而，在常壓下以150 °C加熱合成之ZnO奈米顆粒則仍然幾乎是在非晶相(amorphous)的狀態。特別的是，此原位高壓水熱法不但可以在P3HT奈米線上直接合成出具高結晶性的ZnO奈米顆粒，亦同時可以達到提升P3HT結晶度的效果。藉由光學物理的分析顯示此P3HT/ZnO奈米混成材料的確具有較佳之UV吸收、良好之螢光淬熄(PL quenching)效應，以及較短的激質生命週期。這些光電特性的提升代表著此P3HT/ZnO奈米線結構符合預期地提供了大量的激質分離界面及連續的網絡來傳輸電荷。
在第三個部分裡，一種含有全共軛鏈段之嵌段共聚高分子poly(2,5-dihexyloxy-p-phenylene)-b-poly(3-hexylthiophene) (PPP-b-P3HT)被用來取代先前的P3HT當作線性模板來製備具高規整度之核/殼型奈米線混成系統。PPP-b-P3HT在這個系統中可作為具自組裝能力的模板分子亦可作為有效的電子提供者。同樣的，以此高壓水熱法(~7 bars)亦成功地在相對低溫之130 °C下製備出之具高結晶度之TiO2奈米顆粒。值得注意的是，經由X射線光電子能譜(XPS)的證明，鈦前驅物及TiO2奈米顆粒傾向於和PPP鏈段上的氧原子作用，而不是去和P3HT鏈段上的硫原子作用。此合成出之PPHT/TiO2混成系統會自組裝成為一核/殼型奈米線結構，其線寬約36 nm，而且絕大部分之TiO2奈米顆粒是存在於非晶相的PPP鏈段之中。同時，經由低銳角入射廣角X光散射實驗(GIWAXS)確認了此原位高壓水熱法可以協同性地合成出具有高結晶度的P3HT奈米線以及TiO2奈米顆粒。因此，以此方法製備出的PPHT/TiO2混成材料亦具有大面積的激質分離界面及連續的電荷傳輸網絡，表現出優異的螢光淬熄效應。基於以上之研究開發，這本論文揭示了一種極具潛力的方法以利用原位方式製備有機/無機奈米混成材料，且這樣的材料是可以由各種不同的導電共軛高分子和無機奈米顆粒來搭配組成，可以預期此材料在未來諸多先進光電元件中相當具有應用發展性。
Organic/inorganic hybrid structures are promising systems for a variety of optoelectronic applications because of their low cost, flexibility, light weight, and ease of large-scale production. However, the ability to control the morphology for obtaining large area of interfaces and continuous pathway for enhanced functional properties is still an important issue that needs to be overcome. In this work, we developed a novel in situ high pressure hydrothermal method to fabricate self-assembled π-conjugated polymer/inorganic nanoparticles hybrid nanowires. In the first part, wherein a facile one-step synthetic strategy was utilized to co-organize conducting polymer, poly(3-hexylthiophene) (P3HT), and titanium precursors into highly elongated hybrid nanowires, followed by a hydrothermal process in an autoclave to in situ transform the titanium precursors into crystalline TiO2 nanoparticles on the P3HT nanofibrils. P3HT nanofibrils were utilized as a structure-directing motif to achieve a favorable dispersion of electron acceptor (A) TiO2 nanocrystals of 10-15 nm in diameter embossed along the nanofibrils, as well as an efficient electron donor (D) for the nanohybrid. Particularly, the crystallization temperature of anatase-phase TiO2 nanoparticles with high crystallinity via the hydrothermal method was significantly reduced to 130 °C in an elevated pressure of ~7 bars as compared to the conventional calcination temperature of 450 °C at ambient pressure for TiO2 nanocrystal synthesis, therefore, allowing the synergistic one-step fabrication of both highly crystalline TiO2 nanoparticles embossed on highly crystalline long-range ordered P3HT nanofibrils. As a consequence of the structural development, this P3HT/TiO2 embossed nanohybrids could afford significant improvements in their D/A interfacial contact area for effective charge separation without the need of capping ligands typically used in ex-situ D/A blend systems, as well as efficient pathway for charge transport, leading to enhanced optoelectronic properties and device performance. The highest conversion efficiency of 0.14% was presented from the P3HT/TiO2 embossed hybrid device, which was a remarkable improvement as compared to only 0.03% from an ex-situ P3HT/TiO2 hybrid device.
In the second part, we carried out a systematic investigation using a hydrothermal process to fabricate P3HT/ZnO nanohybrids thin film comprising of ZnO nanocrystals embossed on self-assembly P3HT nanofibrils which were more than 500 nm in length along its fibril long-axis with an average fibril width of ~24 nm. The sulfur atoms at the thiophene ring of the P3HT molecules were used to act as anchoring sites with zinc oxide precursors for the formation of zinc-sulfur complexes, followed by utilizing the hydrothermal crystallization process at an elevated pressure (~9 bars) in an autoclave to grow highly crystalline ZnO nanoparticles in situ on the existing P3HT nanofibrils. The coordinate bonding between P3HT and ZnO nanoparticles carried advantages over a randomly distributed hybrid system, resulting in a better control of morphology to achieve a favorable dispersion of nanocrystals in this hybrid system. The high pressure hydrothermal process demonstrated the ability to synthesize highly crystalline monophasic wurtzite-type ZnO nanoparticles situated on P3HT fibrils under relatively low temperatures (150 °C), while the ZnO nanoparticles in the other P3HT/ZnO hybrid sample prepared via a thermal oxidation treatment at 150 °C in ambient air remained mostly amorphous. In particular, the in situ hydrothermal process can not only be used to synthesize highly ordered ZnO nanocrystals embossed on P3HT nanowires, but also to synergistically enhance the crystallinity of P3HT nanofibrils due to the hydrothermal method at elevated pressure appears to have no adverse effect on the physical and chemical properties of P3HT. Photophysical property analysis showed that the P3HT/ZnO hybrid thin films exhibited enhanced vibronic absorption, photoluminescence quenching, and shorter exciton lifetime. The enhancement in these optoelectronic properties indicated that the ZnO embossed nanofibrillar structure was expected to provide a large area of D/A interfaces for efficient excitons dissociation as well as a continuous pathway for charge transport, thereby improving the optoelectronic properties.
In the third part, an all π-conjugated diblock copolymer poly(2,5-dihexyloxy-p-phenylene)-b-poly(3-hexylthiophene), PPP-b-P3HT was used as a linear nanotemplate for the synthesis to yield nanohybrids with highly ordered donor/acceptor (D/A) core-shell nanowire structure that exhibit enhanced optoelectronic properties. The diblock copolymer of PPP-P3HT was used as both a synergistic long-range ordered structure-directing template and an efficient exciton donor for the nanohybrids. The novel in situ high-pressure hydrothermal process provided us a facilitating way to fabricate PPP-P3HT/TiO2 nanohybrids with highly crystalline TiO2 nanoparticles at a reduced temperature of 130 °C in an elevated pressure of ~7 bars. In particular, as evidenced by the XPS measurements, the titanium precursors and TiO2 nanoparticles were surrounded and interacted with the oxygen atoms on the side chains of PPP block rather than the sulfur atoms of thiophene on main chains in this diblock copolymer/TiO2 hybrid system. Therefore, the synthesized PPP-P3HT/TiO2 nanohybrids self-assembled into a 1-D D/A core-shell nanowire structure of uniform width (~36 nm), wherein the TiO2 nanoparticles were embedded in the amorphous PPP phase mostly. Meanwhile, the GIWAXS results confirmed that the novel high pressure hydrothermal treatment was an effective methodology to synergistically fabricate organic/inorganic hybrid materials with high crystallinity for both the PPP-P3HT copolymer and TiO2 nanoparticles. Thus, the resulting PPP-P3HT/TiO2 hybrid material displayed a considerably enhanced PL quench effect due to the TiO2 embossed nanofibrillar structure could provide enhanced D/A interfacial area for charge separation as well as an efficient pathway for charge transport between the PPP-P3HT copolymer and the confining TiO2 nanoparticles in the desired domain. Base on the promising developments, this work can pave a potential way to apply the in situ approach for fabricating organic/inorganic nanohybrid materials consisting of conjugated polymers with different inorganic nanoparticles for future advanced applications in optoelectronic devices.
|Appears in Collections:||化學工程學系|
Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.