三重陽離子鉛鹵化物鈣鈦礦藉由光及濕潤氧氣降解機制的研究

Degradation of Triple Cation Lead Halide Perovskite Induced by Light and Ambient Gases

陳聖羱(Sheng-Yuan Chen)

指導教授 ： 楊耀文

國立清華大學/理學院/化學系所/碩士(2017年)

摘要

現今鈣鈦礦太陽能電池的轉換效率提升地非常迅速，其轉換效率已經可以到達22.1%，不幸地是鈣鈦礦材料在大氣中相當不穩定。本研究製作三重陽離子混和鹵素的鈣鈦礦，利用了較為安定的銫離子取代甲脒以及甲基胺離子的位置，然而最優化的銫離子添加比例是10%，即Cs0.1(FA0.83MA0.17)0.9Pb(I0.83Br0.17)3，此元件的表現是最好的，其效率可達15.3%，並以此三重陽離子鈣鈦礦進行降解機制研究。我們將鈣鈦礦置入於不同環境中6小時，環境分別有:乾燥氧氣、濕潤氮氣、濕潤氧氣，並同時以AM15的光照射鈣鈦礦。將處理過後的樣品利用XPS、XRD、UV-vis和SEM來推演鈣鈦礦降解機制。研究結果顯示，碳陽離子甲基胺特別易與水反應而形成氣態胺逃離鈣鈦礦，而甲脒則會進行一連串的水解反應。對於三個陽離子來說，穩定度是銫離子最為安定，再來是甲脒，最後是甲基胺，而中心金屬鉛會被氧氣氧化成氧化鉛，然而在有照光的環境下，鈣鈦礦有明顯的被破壞，其降解速率會增加許多，在許多文獻中也指出了照光後的鈣鈦礦會與氧氣反應成超氧化物(superoxide)，而反應性強的超氧化物與鈣鈦礦進行不可逆的反應，加速地破壞鈣鈦礦結構，在照光的環境下，也發現了碘離子和溴離子會形成氣態碘化氫和溴化氫逃離鈣鈦礦。鈣鈦礦在有水氣和氧氣以及照光的環境下，水氣以及superoxide的破壞是同時進行的。

關鍵字

鈣鈦礦 ； 降解機制 ； 三重陽離子 ； 銫

並列摘要

The power conversion efficiency of hybrid perovskite (PSK) solar cells already exceeds 22%. Unfortunatley, perovskite materials are unstable in ambient operating condition. In this study, we first reported the fabrication of triple-cation, mixed halide PSK materials that contain methylammonium (MA), formamidinium (FA), and cesium with the expected improvement of stability. The stoichiometry of the best film was optimized to be Cs0.1(FA0.83MA0.17)0.9Pb(I0.83Br0.17)3 based on the solar cell performance that reached 15.3%. The comparative stability test was performed with the PSK films irradiated with AM1.5 light while exposed to three types of gaseous ambient for 6 h: dry O2, moist N2, and moist O2, respectively. The as-treated PSK films were then analyzed with XPS, XRD, UV-vis, and SEM in order to derive at the degradation pathway. The degradation products include amines after PSK reaction with O2 and H2O. The relative stabillity of three cations increases from MA to FA and then Cs. The formation of PbO can be identified. Furthermore, the rate of perovskite degradation is accelerated by the superoxide formed from oxygen molecules with electrons generated from light absorption of perovskite. The gaseous HI and HBr are formed after a series of successive reactions. The PSK degradation becomes most severe under the condition where water and oxygen are simultaneously present.

並列關鍵字

perovskite ； degradation ； triple cation ； cesium

參考文獻

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