鈣鈦礦MAPbI3-xBrx兩階段塗佈製程之機制研究

Unraveling two-step growth process of perovskite MAPbI3-xBrx

鍾昀庭(Yun-Ting Chung)

指導教授 ： 王玉麟

共同指導教授 ： 王俊凱(Juen-Kai Wang)

國立臺灣大學/理學院/物理學研究所/碩士(2019年)

https://doi.org/10.6342/NTU201904265

摘要

有機-無機鈣鈦礦材料—甲基胺基碘化鉛(MAPbI3)—因為其擁有良好的光電特性以及簡易的溶液製備流程，在近年來成為一極具潛力的太陽能與光電材料。然而時至今日，該材料製備的生成機制仍不清楚，導致現今對於光電特性、或是半導體元件的研究僅能依靠經驗法則或試誤學習。為了拓展對於反應機制的了解，這份研究採用兩種方法，針對兩階段溶液製程—浸泡碘化鉛（PbI2）於含有甲基碘化胺（MAI）的溶劑中—進行探討。第一，將反應物MAI替換成甲基溴化胺（MABr），溴離子可以幫助區分原先製備過程中，來自於溶液的碘離子以及來自PbI2的碘離子。第二，吸收光譜與X光晶格繞射量測分別檢測了生成的鈣鈦礦材料中溴成分的演變。此兩種方法提供了一致的結果。實驗的證據指出以下三個階段：（１）高溴含量的混和鹵素鈣鈦礦MAPbI3-xBrx快速地在表面生成；（２）隨著反應進行，溶液中的離子逐漸擴散進入深層的PbI2，而形成的MAPbI3-xBrx中溴含量逐漸降低至與碘相當的中等含量；（３）當所有的PbI2都轉換成MAPbI3-xBrx，因為持續進行的離子交換而使溴的含量逐漸增加。我們提出的模型描述了MAPbI3的生成過程：在反應之初，PbI2的碘主導了MAPbI3的生成，而溶液中的碘則透過陽離子交換將殘餘的PbI2轉換成MAPbI3。此外利用溴來解析MAPbI3-xBrx生成過程，也提供了設計混合鹵素鈣鈦礦MAPbI3-xBrx的製備原則。

關鍵字

有機-無機鈣鈦礦 ； 混和鹵素鈣鈦礦 ； 兩階段溶液製程 ； 吸收光譜 ； X光繞射

並列摘要

Methylammonium lead trihalide (MAPbI3) has demonstrated its potential in solar-cell applications and other opto-electronic applications due to its great optical and electrical properties as well as ease of growth with simple solution-processing methods. Given its recent progress, the mechanisms of the solution-processing growth methods remain unclear, making controlling the grown materials still rely on try-and-error. This study aimed to unravel the process of two-step solution-growth method—immersing lead iodide (PbI2) film into methylammonium iodide (MAI) solution—with two measures. First, replacing the MAI solution with methylammonium bromide (MABr) solution would help differentiate the respective roles of the iodide in solution and the iodine atoms in the PbI2 film. Second, optical absorption spectroscopy and X-ray diffraction were used to reveal the evolution of the Br composition of the grown MAPbI3-xBrx. The extracted evolution of the Br composition from the results of optical absorption spectroscopy and X-ray diffraction coincidently agreed. The experimental results showed that the process can be described in three stages: (1) MAPbI3-xBrx with high Br composition is promptly grown on the top layer; (2) the Br composition then decreases in time to reach a medium value as the PbI2 film reacts with the permeated MA cations and Br anions; (3) upon the PbI2 film is converted completely, the Br composition increases in time via iodide-bromide exchange. The proposed model helps reveal the roles of two different sources of iodine: the iodine in the PbI2 film dominates the grown MAPbI3 film initially, while the iodide in solution takes part in the grown film in the end through anion exchange. The extracted evolution of the Br composition in the grown MAPbI3-xBrx provides a guideline to grow MAPbI3-xBrx with a designated bromine composition for specific opto-electronic applications.

並列關鍵字

organic-inorganic perovskite ； mixed-halide perovskite ； two-step solution-growth method ； optical absorption spectroscopy ； X-ray diffraction

參考文獻

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