甲基胺基碘化鉛（methylammonium lead iodide, MAPbI3）為近年來新興的有機
金屬鹵化鈣鈦礦太陽能電池材料，目前在電阻式記憶體(Resistive Random-Access
Memory, RRAM)上的應用研究也是逐漸興盛，但是 MAPbI3 的穩定性是一大缺點，
大氣環境下的水氣與氧氣都會造成材料的劣化。本研究以導電原子力顯微鏡
(Conductive Atomic Force Microscopy, C-AFM)模式量測甲基胺基碘化鉛薄膜在劣化
過程中微區電流-電壓特性(I-V 特性)的變化，並藉 AFM 的奈米力學(Quantitative
Nanoscale Mechanical, QNM)模式量測不同時間下的楊氏係數變化來輔助說明 CAFM 所觀測的結果。實驗結果發現劣化過程的 I-V 電性變化主要可分成三個階段。
在第一階段初始狀態(3 小時)元件並沒有明顯的電阻切換特性出現，經過 3.5 小時後
材料開始表現出明顯記憶行為(遲滯行為)，推測因為施加電場所導致的(碘)離子遷移，
形成導電細絲通道，使開關比(ON/OFF Ratio)上升。且晶界區域出現較明顯的 Builtin Potential Difference(ΔVB)，可能是晶界區域有較明顯的離子遷移現象所導致。第
二階段的特徵為ΔVB 的消失跟晶界處的電流下降，我們在 QNM 結果中發現整體楊
氏係數下降，可能是低結晶度的碘化鉛覆蓋於表面並屏蔽了晶界區域離子的移動，
使晶界區域的離子遷移效應減弱及導電性下降。同時我們在 I-V 特性中看到了負微
分電阻(Negative Differential Resistance Effect, NDR Effect)效應，基於前人的研究結
果推測原因為劣化過程中有大量碘空位在材料介面生成，使施主型介面(Donor-like
Interface)的發生，導致 NDR 現象。第三階段由 C-AFM 結果看到整體的導電性下降，
以及電阻切換特性下降和 NDR 效應消失，QNM 中發現楊氏係數快速上升，可能為
碘化鉛緻密化所致。
為了改善 MAPbI3的穩定性，本研究導入三甲氧基矽烷((3-
Aminopropyl)trimethoxysilane，APTMS)的製程，在 MAPbI3 的上方或底部分別鍍製II
APTMS 以減緩材料的劣化速度。結果發現，在 MAPbI3 上覆蓋 APTMS 後，劣化過
程中的開關比變異度較純鈣鈦礦試片小，另外初始狀態的 I-V 圖中晶界區域並沒有
ΔVB 的產生，表示 APTMS 在晶界區域的鈍化效果更為顯著。同時在 QNM 結果中
發現鍍製 0.5 天後純 MAPbI3試片的晶粒尺寸會增加約 150 nm，而覆蓋 APTMS 試片
只增加了 20 nm，代表 APTMS 覆蓋於 MAPbI3上方能夠改善 MAPbI3晶面特性並有
助於隔絕水氣。另一方面發生 NDR 機率較純鈣鈦礦的試片低，由於 NDR 的發生可
能與鈣鈦礦的缺陷有關，代表 MAPbI3上方加入 APTMS 後可以抑制材料缺陷的出現。
在底層鍍上 APTMS 後發現 XRD 圖譜中 MAPbI3的繞射峰訊號明顯上升，說明在底
部加入 APTMS 後可以提升材料的結晶度。由電性量測結果我們發現在劣化過程中
整體的開關比分布均在 1~100 的範圍內，較純 MAPbI3 試片的分布範圍集中，另外
在晶界區域並未發現ΔVB 的出現，推測可能原因是 APTMS 中的分子基團特性可以
提升材料的穩定度。同時我們發現在底層加入 APTMS 後試片第三天開始出現 NDR
現象，且 NDR 出現機率較純 MAPbI3試片低，表示在 MAPbI3與 ITO 基板的介面加
入 APTMS 後可以抑制材料中的缺陷產生。在 QNM 結果中發現，楊氏係數開始下降
以及再度上升的時間點較純 MAPbI3 試片延後，顯示高結晶度有助於延遲劣化的發
生。
總結來說，在上方與底部加入 APTMS 後均發生以下現象。從 C-AFM 的結果發
現導入 APTMS 後晶界區域的電流明顯下降，並且在該處沒有出現ΔVb，表示
APTMS 中的極性分子基團對於晶界的影響顯著，能抑制晶界區域離子遷移的現象。
同時加入 APTMS 後可以發現 NDR 現象的出現機率明顯下降，顯示 APTMS 可以抑
制缺陷的發生並鈍化表面。最後，我們將 APTMS 的製程導入 MAPbI3 RRAM 的元
件中，在元件製備完成後第七天的 I-V 量測結果中發現，有加入 APTMS 的元件
ON/OFF Ratio 的變異明顯減少，說明導入 APTMS 後可以增加元件的操作穩定性，
因此日後可望導入 APTMS 製程可以減緩劣化速度並有效提升元件的穩定度。

Methylammonium lead iodide (MAPbI3) is a newly developed solar cell material for the organo-metal halide perovskite. Recently, resistive random access memory (RRAM) is also gradually flourishing. Hence, the stability of MAPbI3 is still a significant drawback because the water vapor and oxygen in the atmospheric environment would cause material degradation. In this study, we apply Conductive Atomic Force Microscopy (C-AFM) to measure the I-V characteristics of the micro area of MAPbI3. The changes of Young's Modulus at different times measured by the Quantitative Nanoscale Mechanical (QNM) mode of AFM are used as supplement of the C-AFM results.
The results show that the degradation of MAPbI3 mainly takes place in three stages. In the initial state, there are no noticeable resistance switching features seen in MAPbI3 thin film. After applying electric fields caused by iodine ion migration, the formation of conductive filament channel makes the ON/OFF Ratio increase according to memory (hysteresis) behavior of MAPbI3 caused by ion migration. In the second stage, lead iodide with low crystallinity is covered on the surface of MAPbI3, shielding the movement of ions in the grain boundary area of MAPbI3, making the disappearance of ΔVB and eventually the current at the grain boundary decrease. Meanwhile, the iodine vacancies on the surface of the MAPbI3 will lead to the appearance of donor-like interfaces. Negative Differential Resistance Effect (NDR Effect) could be found in some I-V curves. In this stage, Young's Modulus in QNM maps also decreases, further confirming the formation of low crystallinity lead iodide.
In the third stage, C-AFM shows that the overall current decrease and the NDR effect disappears. The reason may be lead iodide covering the surface, and become dense theheby blocking the transfer of electrons under electric field. Also, QNM results illustrate that Young's Modulus rapidly increases, thus confirming lead iodide densification.
The process of (3-aminopropyl)trimethoxysilane (APTMS) was introduced in this study to improve the stability and slow down the degradation rate of MAPbI3. APTMS was deposited on the top and bottom of MAPbI3, respectively to see the variation of passivation above and below the active layer.
The results show that APTMS coating on MAPbI3 has a smaller switching Ratio variation than that of the bare perovskite sample in the degradation process. In addition, no ΔVB is found in the grain boundary region in the I-V diagram of the initial state, indicating that APTMS has a more significant passivation effect in the grain boundary region. At the same time, it was found in the QNM results that after 0.5 days of degradation, the grain size of the bare MAPbI3 sample increased by about 150 nm, while at the sample which coated APTMS on top of MAPbI3 only increased by 20 nm, indicating that APTMS covering the top of MAPbI3 can improve the crystal plane properties of MAPbI3 and help to insulate MAPbI3 from water vapor. At the same time, the probability of NDR is lower than that of bare perovskite samples. As mentioned in the previous paragraph, the occurrence of NDR may be related to the defects of perovskite, which means that the addition of APTMS on MAPbI3 film can reduce the occurrence of material defects. Meanwhile, the size of the grain was significantly lower, and it was found in the QNM results that the grain size did not increase significantly after 0.5 days, indicating that the addition of APTMS above MAPbI3 could improve the characteristics of the grain surface and block the entry of moisture. After APTMS coated on the bottom of MAPbI3, it was found that the diffraction peak signal of MAPbI3 and MAPbI3 in XRD results was significantly increased, indicating that APTMS adding on the bottom can improve the crystallinity of the material. In the electrical property measurement results, it was found that the overall switching Ratio distribution was in the range of 1-100 during the degradation process, which was more concentrated than that of bare MAPbI3. In addition, ΔVB was not found in the grain boundary region, which was speculated to be the molecular group properties in APTMS that could increase the stability of the material. At the same time, we found that the occurrence time of NDR in the sample was on the third day of degradation, and the occurrence probability of NDR in this sample was lower than that of bare MAPbI3, indicating that the addition of APTMS at the interface between MAPbI3 and ITO could inhibit the generation of defects in the material.
In summary of the above two paragraphs, the following phenomena occurred after APTMS was added at the top and bottom of MAPbI3. From the C-AFM results, it was found that the current in the grain boundary area decreased significantly after APTMS was introduced, and Δ VB did not appear there, indicating that polar molecular groups in APTMS had a significant influence on grain boundary. It can inhibit ion migration in the grain boundary region. At the same time, the occurrence probability of the NDR phenomenon was significantly reduced after APTMS was added, indicating that APTMS could inhibit the occurrence of defects and passivate the surface.
On the other hand, MAPbI3 was applied to the RRAM device, and the I-V measurement results on the 7 days after the device were prepared showed that the variation of ON/OFF Ratio of the device with APTMS was significantly reduced, indicating that the operating stability of the components can be increased after introducing APTMS. Therefore, it is expected that APTMS will be introduced in the future to slow down the degradation rate and effectively improve the stability of the components.

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