三維石墨烯與矽之蕭基接面於增進光電化學元件穩定度及效能之研究

Three-dimensional Graphene-Silicon Schottky Junctions to Enhance Stability and Performance of Photoelectrochemical Cells

顧哲魁(Che-Kuei Ku)

指導教授 ： 陳俊維

國立臺灣大學/工學院/材料科學與工程學研究所/碩士(2018年)

https://doi.org/10.6342/NTU201803088

摘要

光電化學於水分解的應用為一對環境無害的再生能源，並於近年來受各界的關注，其中，矽自1976以來，因為其較小的能隙以及能帶邊緣與產氫電位匹配，所以廣泛的應用於光電化學的電極材料。近年來，由於單層碳原子所組成的石墨烯擁有出眾的光、電、化學特性，使其成為光電化學元件的組成材料；此外，石墨烯可以與矽形成蕭基接面，高效率的載子分離能力與惰性保護能力，大幅度提升光電化學元件的效能以及穩定度。然而，矽基板本身具有極高的反射率，因此僅有少部分的入射光可以被元件應用，造成效能低落，因此如何降低矽的反射率並增進石墨烯與矽之蕭基光電化學元件的效能將會是我論文的研究主體。在論文的第一部分，我們將石墨烯與矽之蕭基接面建立於抗反射處理過的金字塔型矽基板上，使用新的高分子EVA作為支撐層，讓石墨烯可以與金字塔的各個部分緊密貼合，在藉由微觀下的分析技術，例如掃描式電子顯微鏡、歐傑電子能譜、及掃描穿透式電子顯微鏡，成功並且確切地證明石墨烯與抗反射處理的金字塔矽基板能緊密形成三維度的蕭基接面。第二部分中，將應用這劃時代的蕭基接面於光電化學的量測，因為金字塔型的矽基板增進了入射光的吸收，使得元件的飽和電流上升到42.5 mA/cm2，在經過光觸媒白金的沉積之後，將起始電壓右移至0.3 V vs. RHE。而在長時間的穩定度量測後，我們發現石墨烯的惰性保護能力在金字塔型的矽基板上仍然十分出色。此外，我們也分析了光觸媒白金於三維石墨烯與矽之蕭基接面上的沉積機制，同時也發現了沉積型態的可調控性。

關鍵字

石墨烯 ； 蕭基接面 ； 抗反射 ； 光電化學元件 ； 產氫反應 ； 光陰極 ； 光沉積

並列摘要

Photoelectrochemical (PEC) water splitting has drawn lots of attention as an eco-friendly technology for renewable energy. Since 1976, silicon, whose band gap is smaller, and band edge position overlaps the potential of hydrogen evolution, has been widely used as the electrode in PEC devices. Recently, graphene, an atomic-layered carbon-based material with extraordinary properties, has been introduced to this field to form Schottky junction with silicon. The high efficiency of charge separation and passivation of graphene-silicon Schottky junction indeed enhanced the performance and stability of PEC devices. However, the high reflectivity of silicon substrates has been a big issue in harvesting solar energy. Therefore, how to solve the problem of reflectivity and improve the performance of devices is my thesis topic.At the beginning of my thesis, we try to build graphene-silicon Schottky junction on the anti-reflective pyramid silicon. With the introduction of the EVA transfer method, the quality and integrity of graphene are perfect on the pyramid silicon. The precise analyze, like SEM, AES, and STEM, prove that we successfully create the three-dimensional graphene-silicon Schottky junction on each part of the pyramid silicon. Next, this new epoch-making Schottky junction is utilized to improve the performance of PEC. Due to the increment of harvested incident light, the saturation current reaches 42.5 mA/cm2, and, after the deposition of Pt particles, the onset potential shifts positively to 0.3 V vs. RHE. Graphene layer protects the pyramid silicon very well after we finished a 30-hour-long measurement of stability. Moreover, the tunable morphology of deposited Pt on the graphene/pyramid-silicon is investigated, and we also hypothesize the intriguing mechanism. Due to these result, the three-dimensional graphene-silicon Schottky junction is a promising structure for future utilization of solar energy.

並列關鍵字

graphene ； Schottky junction ； anti-reflection ； photoelectrochemical cell ； hydrogen evolution reaction (HER) ； photocathode ； photo-deposition

參考文獻

REFERENCE

1. Boehm, H.-P., et al., Das adsorptionsverhalten sehr dünner kohlenstoff‐folien. Zeitschrift für anorganische und allgemeine Chemie, 1962. 316(3‐4): p. 119-127.

2. Landau, L., Zur Theorie der phasenumwandlungen II. Phys. Z. Sowjetunion, 1937. 11(545): p. 26-35.

3. Novoselov, K.S., et al., Electric field effect in atomically thin carbon films. science, 2004. 306(5696): p. 666-669.

4. Young, R.J., et al., The mechanics of graphene nanocomposites: A review. Composites Science and Technology, 2012. 72(12): p. 1459-1476.