鈣鈦礦在變溫環境下太赫茲光譜的聲子模態與晶相研究

Annealing Temperature Dependence of Phonon Modes and Crystallinity on Perovskites Studied by Terahertz Spectroscopy

陳廷揚(Ting-Yang Chen)

指導教授 ： 安惠榮

國立交通大學/電機學院/光電工程系所/碩士(2019年)

摘要

混合鹵化鈣鈦礦已成為最有前景的太陽能電池材料之一，因為它們具有製造簡單，成本低，吸收強，移動性好等優點。現在鈣鈦礦太陽電池的效率已達到22.5 %以上。最近，二維(2D)鈣鈦礦在發光元件方面備受注目。一些研究指出，二維鈣鈦礦在一班環境下具有更高的穩定性，而熱穩定性是室外應用的另一個非常重要的特性。在本篇論文中，我們採用穿透式時域解析太赫茲光譜研究烷基銨碘化鉛(XAPbI3)的低頻聲子振動模式；乙基銨(EAPbI3)，丙基銨((PA)2PbI4)和丁基碘化鉛碘化物((BA)2PbI4)。我們發現，隨著有機碳鍊長度的增加，使Pb-I鍵合長度發生變化，使得在太赫茲光譜上看到藍移的現象。為了理解層狀鈣鈦礦的熱穩定性，我們測量了不同溫度下的聲子模態。對於三維鈣鈦礦，CH3NH3PbI3 (MAPbI3)，當溫度達到約65 ℃時，觀察到聲子模態有藍移發生，這是因為發生了由四方相位轉變為立方相位的相變。當用單層石墨烯或過渡金屬二硫屬化物覆蓋時，則未觀察到模態頻率的藍移，這意味著鋪上二維材料可以改善其熱穩定性。而溫度升高到100 ℃時，我們發現層狀鈣鈦礦在1.5和2 THz的聲子模態則幾乎不變，這表示2D鈣鈦礦的高熱穩定性。而在 XRD的結果，可以發現二維鈣鈦礦的熱退火改善了有序相的結晶度。

關鍵字

鈣鈦礦 ； 變溫太赫茲光譜 ； 聲子模態 ； 晶相

並列摘要

Hybrid halide perovskites have become one of the most promising solar cell materials, due to their great advantages of simple fabrication, lower cost, strong absorption, and good mobility. There have been tremendous efforts to improve the conversion efficiency of perovskite-based photovoltaic devices and now it reaches over 22.5 %. Recently, two-dimensional (2D) perovskites have attracted great attention in light emitting device community. Some studies have pointed out that 2D perovskites have higher stability under atmospheric environment. The thermal stability is another very important property for the out-door applications. In this work, we employed the broadband time-domain terahertz spectroscopy to study the low frequency phonon vibration mode of the alkylammonium lead iodides (XAPbI3); ethylammonium (EAPbI3), propylammonium ((PA)2PbI4), and butylammonium lead iodide ((BA)2PbI4). We found that the phonon mode corresponding to the bending vibration of I-Pb-I disappears for three layered perovskites and those at 1.5 and 2 THz due to the bonding length variety of Pb-I blueshift as the length of alkylammonium chain increases. In order to understand the thermal stability of layered perovskites, we measured the phonon modes under different thermal annealing temperatures. For three-dimensional perovskite, CH3NH3PbI3 (MAPbI3), the onset of blueshift of phonon mode is observed when the temperature reaches at about 65 ℃, where tetragonal-to-cubic phase transition occurs. When covered with monolayer graphene or transition metal dichalcogenides, the blueshift of mode frequency was not observed, implying the improvement thermal stability. For layered perovskites, the phonon modes at 1.5 and 2 THz is nearly unchanged as the temperature increases upto 100 ℃, indicating high thermal stability of 2D perovskites. The x-ray diffraction measurements show that the thermal annealing of 2D perovskites improves the crystallinity to ordered phase.

並列關鍵字

perovskite ； In-situ terahertz spectroscopy ； phonon mode ； crystallinity

參考文獻

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