Graphene and Hybrid Perovskite Materials for Electronic and Electrochemical Devices

• Other Authors: Zhou, Shuang (author.)
• Format: Others
• Language: English; Chinese
• Published: 2016
• Online Access: http://repository.lib.cuhk.edu.hk/en/item/cuhk-1292434

為了滿足全球對可持續能源和清潔環境日益增長的需求，發展新材料和有實際應用價值的能源器件是非常意義深遠的。在眾多新興的能源材料中，基於石墨烯的二維（2D）材料以及雜化鈣鈦礦材料在全世界範圍內獲得了廣泛的關注和研究興趣。本博士畢業論文詳細闡述了我在開發新材料的製備方法和基於合成的材料所開拓的電子和電化學器件方面的研究成果。 === 首先，我們使用常壓化學氣相沉積法（APCVD）在銅箔上合成了高質量的二維石墨烯。并展示了利用十八烷基磷酸單分子層修飾的溶液法所製備的雙層金屬氧化物（Al2Oy/TiOx,縮寫為ATO）作為高介電常數的介電層所裝配的低電壓背柵石墨烯場效應晶體管（GFETs）。得益于高質量的介電層和高質量的石墨烯層，器件在一個很小的柵電壓範圍內（-3.0伏到3.0伏）表現出來的空穴載流子遷移率在室溫下可以高達5805 cm2 V-1 s-1,電子遷移率可以達到3232 cm2 V-1 s-1。該研究提出了用一種有效的辦法可以在室溫下實現低電壓高遷移率的石墨烯場效應晶體管器件。此外，基於該器件結構，我們開發了一個策略，通過使用聚乙烯乙胺（PEI）來修飾器件界面以提高電子遷移率。修飾之後的器件顯示出了增強的器件性能，其中電子遷移率已高達6814 cm2 V-1 s-1,同時接觸電阻也降低至45歐姆。根據對比試驗研究，我們發現提高的電子遷移率主要是由PEI對金屬和石墨烯接觸界面的修飾作用決定的。 === 虽然二维石墨烯有很多优势，并能很好的用于电子器件中，但是仍有一应用是需要石墨烯的三维结构的性质。在这一部分，為了實現多孔三維（3D）石墨烯結構，以降低劇烈的層間團聚，我們闡示了一種低溫（650oC）APCVD生長方法，可以在微米級的鎳顆粒上合成高質量的彎曲石墨烯。同時系統地研究了生長溫度和顆粒尺寸對彎曲石墨烯形貌的影響，并可以將實驗結果與之前的石墨烯生長理論模型關聯起來，表明在鎳顆粒上呈現的大量原子級別的台階邊緣可以有效的促進甲烷分解，石墨烯形成和缺陷愈合。得益于彎曲的幾何結構，彎曲石墨烯在用作電極材料時，在KOH電解液中有203.4 F g1的比電容。兩電極測試表現出了出色的電化學性質，其中能量密度高達40.9 Wh kg-1，功率密度高達70 W kg-1，以及擁有長期的穩定性。與此同時，我通過探究彎曲石墨烯在其他過渡金屬顆粒上的生長，指出了另外一個不同的生長機理，以及表明了該生長方法可以用于生長不同3D石墨烯材料的通用性。 === 在第二部分展示的电化学电容器，是一种电化学器件，可以有效的分离离子导电性和电子导电性。所以在本毕业论文的第三部分，我還探究了另外一種新興的能源材料，有機金屬鹵化鈣鈦礦的電化學性質。一種基於有機鉛三碘化鈣鈦礦的薄膜電化學電容器（EC）被展示具有優良的循環性能。通過系統的對不同電解液和不同厚度的鈣鈦礦薄膜的電化學測試研究，鈣鈦礦的雙重傳導（電子傳導和離子傳導）過程被鑒定，并闡釋了鈣鈦礦層不僅能作為電極材料也可以作為一種固體電解液。通過對電化學阻抗譜（EIS）的結果進行電路模擬，鈣鈦礦薄膜中的可移動離子（即離子天然缺陷）密度可以被提取，而該數值比從一般鈣鈦礦電子器件，如太陽能電池估計出來的數值低。該結果表明有機金屬鹵化鈣鈦礦材料中的離子形成和傳輸過程可能更大程度的被自由載流子的流動所激活。 === 本文的最後部分呈現了本博士論文在研究成果和貢獻上的全面總結，并提出了基於二維材料和雜化材料的更多有能源器件的應用方向。 === To fulfill the increasing global demand for sustainable energy and clean environment, it is of great significance to develop not only new materials but also practical energy devices. Among the emerging energy materials, graphene based two-dimensional (2D) materials and hybrid perovskite materials have drawn tremendous attention and research interest around the world. This thesis describes my research efforts in developing new material preparation methods and exploiting the electronic and electrochemical devices based on these materials. === In the first part, high-quality 2D graphene is grown on Cu foil by atmospheric pressure chemical vapor deposition (APCVD) method. A low-voltage back-gated graphene field-effect transistor (GFET) is demonstrated, which employs an octadecylphosphonic acid self-assembled monolayer modified solution-processed bilayer metal oxide (Al2Oy/TiOx, abbrev. as ATO) as the high-k gate dielectric. Owing to the high quality of the gate dielectric as well as the graphene layer, outstanding room-temperature hole mobility up to 5805 cm2 V-1 s-1 and electron mobility of 3232 cm2 V-1 s-1 are obtained in a small gate voltage range from -3.0 V to 3.0 V under vacuum. This study suggests an effective way to realize low-voltage high mobility GFETs at room temperature. Furthermore, based on the device structure, a strategy is developed to enhance the electron mobility with interface modification by poly (ethylene imine) (PEI). The modified device shows an enhanced performance with a high electron mobility (~ 6814 cm2 V-1 s-1) and a low contact resistance (~ 45 ohm). Upon a comparative study, it is found that the high electron mobility is mainly determined by the interface modification at the metal/graphene contact. === Although 2D graphene has a lot of advantages and can be well applied in the electronic devices, there are still some applications that need the three-dimensional (3D) response of graphene based materials. Thus in this part, to achieve porous and 3D graphene structure without severe aggregation, a low-temperature (650 oC) APCVD growth method is demonstrated to synthesize high-quality curved graphene on micron-sized Ni particles. The effects of growth temperature and particle size are systematically studied and the experimental observations can be well correlated with previous theoretical models on graphene growth, suggesting that a large amount of atomic step edges is presented at the Ni particle surface, which facilitate methane decomposition, graphene formation and defect healing. Due to the advantages of curved geometry, the curved graphene used as an electrode material reveals a specific capacitance of 203.4 F g-1 in aqueous KOH electrolyte. Two-electrode supercapacitors (or electrochemical capacitors) constructed with the curved graphene also show outstanding electrochemical properties, such as high energy density (40.9 Wh kg-1) and power density (70 kW kg-1), as well as long-term stability. In addition, other transition metal particles are also explored as the catalysts for the curved graphene growth, and the results indicate a different growth mechanism and the versatility of the present method in producing different kinds of 3D graphene materials. === Electrochemical capacitor, as demonstrated in the second part, is a kind of electrochemical devices, which can effectively decouple the ionic and electronic conduction. Thus in the third part of this thesis, I would like to explore the possibility of such device in the investigation of the ionic properties of an emerging photovoltaic material - organometal halide perovskite. A thin film electrochemical capacitor with excellent cyclability is demonstrated based on organolead triiodide perovskite. With systematical electrochemical characterizations on the cells with different electrolytes and perovskite thickness, dual conduction (electronic and ionic conduction) processes are identified in the perovskite films, revealing that the perovskite serves not only as an electrode but also a solid electrolyte. Through circuit modeling of the electrochemical impedance spectroscopy (EIS) characteristics, the density of mobile ions (i.e. ionic native defects) in the perovskite films is extracted and found lower than those estimated from perovskite electronic devices, e.g., solar cells. The result suggests that the ion formation and transport processes in organometal halide perovskites may largely be activated by the flow of free charge carriers. === In the last part, an overall summary on the findings and contributions of this thesis is present and the future research directions based on graphene and hybrid perovskite materials for electronic and electrochemical devices are proposed. === Zhou, Shuang. === Thesis Ph.D. Chinese University of Hong Kong 2016. === Includes bibliographical references (leaves ). === Abstracts also in Chinese. === Title from PDF title page (viewed on …). === Detailed summary in vernacular field only. === Detailed summary in vernacular field only. === Detailed summary in vernacular field only. === Detailed summary in vernacular field only. === Detailed summary in vernacular field only.