低溫製程電子傳導層應用於鈣鈦礦太陽能電池之穩定度與效率研究

Abstract

本研究以低溫的電子傳導層材料為主，以利於實現低耗能與大面積製程的願景，並從穩定度以及效率將實驗分成兩部分。 第一部份我們做出了一個穩定的元件，其結構為ITO/ZnO/Perovskite/Spiro-OMeTAD/Au，在此實驗中我們證明高功函數金屬Au電極相較於Al, Ag金屬電極來的更穩定，且平板ZnO電子傳導層也比ZnO與TiO2奈米粒子結構穩定，另外我們首度提出一個能減緩水平方向水氧侵蝕的回泡法，此方法快速又可重複使用，從SEM (Scanning Electron Microscopy), XRD (X-Ray Diffraction) 與電流-電壓曲線的證據也顯示退化60天後的元件可以經由回泡法使退化的碘化鉛回復到鈣鈦礦。經由Au電極與平板ZnO電子傳導層保護住鈣鈦礦垂直方向的水氧侵蝕，並利用回泡法保護住鈣鈦礦水平方向的水氧侵蝕，基於這樣的方法與元件結構，我們成功的延長鈣鈦礦太陽能電池的生命期超過4個月也還能持續使用回泡法，另外這元件的生命期也是目前文獻報導的最高值。 第二部份我們利用低溫製程之二氧化鈦奈米粒子結合金奈米粒子作為電子傳導層，利用金奈米粒子在可見光範圍能吸收的特性，去填補二氧化鈦本身因為深層能階缺陷導致的電子不足，從SCLC (Space Charge Limited Current)的測試結果也證明摻雜金奈米粒子後的二氧化鈦電子遷移率上升一個級數，更利於電子的傳遞。此外，我們也利用可熱交聯 [6,6]-Phenyl-C61-Butyric Styryl Dendron ester (PCBSD) 富勒烯衍生物做為有機支架，在XPS (X-ray Photoelectron Spectroscopy) 的證據中也顯示其具有能承載更多鈣鈦礦的潛力，但因為在XPS的鉛訊號提升可能是來自二步法常見的碘化鉛殘留，我們更進一步的提出利用混合溶劑的方法使碘化鉛全轉化成鈣鈦礦，從XRD的證據顯示利用混合溶劑製備的鈣鈦礦吸光層其碘化鉛的特徵峰完全消失，同時從SEM的上方影像呈現可以明顯的看出不同比例的DMSO (Dimethyl Sulfoxide) 加入對其表面形貌與晶粒大小的影響。最後結合金奈米粒子，C-PCBSD，混合溶劑三者的優點，成功的將基於低溫TiO2做為電子傳導層的鈣鈦礦太陽能電池效率從6.3 %提升到17.2 %。

In this research we focused on using the low-temperatured electron transporting layer to realize high stability and high efficiency in perovskite solar cells. In the first part of this study, a novel method was adopted to recharge and rejuvenate the perovskite solar cells by immersing the device into methyl ammonium iodide (MAI) solution and heated at 70 °C for 40 sec. We demonstrated Au electrode as a robust one than Al and Ag electrode for ZnO Planar structures rather than ZnO and TiO2 nanoparticles (NPs). In addition to this, degradation path of device was discussed. The scanning electron microscopy images and X-ray diffraction spectroscopy evidenced that the perovskite crystals have been regenerated after degradation (60 days) with the help of MAI as a rejuvenation agent. After long-term aging test with rejuvenation in 185 days, its PCE value was still around 11 % as compared to the original one of 11.6 %. In the second part of this study, we used the promising low temperature titanium dioxide as an electron transporting layer which was doped with gold nanoparticles to improve the electron mobility, short current and compensating the lack of electron in titanium dioxide deep defects. The SCLC measurement showed that the electron mobility increased one order of magnitude for titanium dioxide doped the gold nanoparticles. Futhermore, C-PCBSD was adopted as an organic cathode buffer layer (scaffold) to increase the lead contents in the active layer which was proved in the XPS measurement. The result demenstrated that the C-PCBSD scaffold had the potential to load more perovskite. Two steps deposition method generally had PbI2 residue which may lead to the increase of Pb signal in XPS measurement. In this study, we used a cosolvent of DMSO and DMF (Dimethylformamide) in the second step so as to ensure the complete conversion of perovskite. Combing the advantage of Au nanoparticles in TiO2, C-PCBSD scaffold and cosolvent. We were able to fabricate a high efficiency perovskite solar cell with PCE value of 17.2 %.