鹵化有機金屬鈣鈦礦－CH3NH3PbI3 於2009 年開始被應用於太陽能電池中、作為高效吸光層材料，到目前為止已發展出多樣的元件結構，其中使用固態電洞傳輸材料作為電解質的元件已可達19.3%的高效率。相對而言，使用傳統含氧化還原對的液態鈣鈦礦太陽能電池雖然具有製程簡單、封裝容易、無須昂貴熱蒸鍍程序等優勢，卻面臨CH3NH3PbI3被含I-/I3-的液態電解質所腐蝕、導致效能衰減的問題，其最高效率僅達6.7%。
為了在不干擾電子傳輸的前提下提升液態鈣鈦礦太陽能電池的效能穩定性，於本研究中使用Spiro-OMeTAD作為CH3NH3PbI3與液態電解質間的保護層，有效讓元件效能穩定性提升。不過，儘管Spiro-OMeTAD保護層有助於穩定性的增進，元件效能衰減與CH3NH3PbI3被腐蝕的問題依舊存在，這除了表示保護層的製備技術須更進一步的改善外，也突顯出瞭解腐蝕現象及其發生的根本原因也相當重要。因此，本研究的後半部分藉由XRD、SEM、EDS、UV-Vis吸收光譜等方式進行分析，得到了以下幾項重要的發現：首先，在LiI/I2（I-/I3-）電解質系統下，對CH3NH3PbI3造成腐蝕的主要來源為I-，I3-則不參與腐蝕反應；其次發現元件裡同時存在有CH3NH3PbI3晶體的溶解與再沉積，使多孔層上出現微米級的巨型晶體；最後，雖然tBP本身極易腐蝕CH3NH3PbI3晶體，但當tBP是以添加劑的方式存在於電解質中時，其反而可填補CH3NH3PbI3晶體上的缺陷、進而穩定晶體，使溶解速率減緩、增進元件效能穩定性。我們認為這些發現，不但有助於理解腐蝕現象的基本原理，亦有利於在未來更進一步提升液態鈣鈦礦太陽能電池的效能與穩定性。

Organometal halide perovskite, CH3NH3PbI3, has been used as light harvester in solar cell since 2009. Perovskite solar cell has been developed diverse structures so far, and the one with solid hole transport material (HTM) as electrolyte has been achieved 19.3% power conversion efficiency. In contrast, liquid electrolyte type perovskite solar cell faces the hurdle of the degradation caused from dissolution of CH3NH3PbI3 by I-/I3--contained electrolyte, even though it possesses several advantages in terms of easy fabrication, simple sealing and no need of expensive vacuum evaporation. Thereby, its highest power conversion efficiency remains only 6.7%.
In this study, we use a commomly-used HTM, Spiro-OMeTAD, as the protecting layer between CH3NH3PbI3 and electrolyte for the purpose of isolating the physical contact of liquid electrolyte and perovskite as well as not interfering the electron transfer from electrolyte to CH3NH3PbI3. This arrangement did enhance device stability significantly but it is also found the corrosion still exists. It not only indicates the coating of protecting layer requires more engineering study but also shows the importance of digging out the root cause for corrosion.
By analyzing the results of XRD, SEM, EDS and UV-Vis spectrum, some important information is concluded. First and foremost, I3- does not involve in the corrosion reaction, while I- is the main origin of corrosion of CH3NH3PbI3 in LiI/I2 (I-/I3-)-contained electrolyte. Besides, dissolution and redeposition of CH3NH3PbI3 take place simutaneously in the device and result in the appearance of giant CH3NH3PbI3 crystals within few micrometers on the mesoporous layer. Last but not least, the common additive, tBP, in electrolyte is found to stabilize CH3NH3PbI3 degradation by filling itself at the defects on crystal, although tBP itself corrodes CH3NH3PbI3. The information discovered in this study is beneficial to understand the fundamentals of corrosion and to further improve the performance of liquid electrolyte type perovskite solar cell.

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