不同二氧化鈦奈米結構的合成與鑑識及其在染料敏化與鈣鈦礦太陽能電池之應用

Abstract

使用一種簡單的水熱合成方法來製備二氧化鈦，其中以異丙醇鈦 (TTIP) 作為前驅物，以三乙醇胺 (TEOA) 作為敖合試劑，在一個含二乙胺 (DEA) 的鹼性環境下，來製備尺寸可調控的銳鈦礦二氧化鈦奈米晶體 (HD1-HD5)。DEA 扮演著晶體成長過程中促使兩階段成長的角色。所製備出的銳鈦礦二氧化鈦八面體形貌奈米晶體尺寸為30-400奈米，如果以HD4做為晶種，連續的水熱過程可以得到長410奈米、寬260奈米，特大的HD5八面體單晶二氧化鈦。一般以30奈米的HD1作為主動層，300奈米的HD5作為散射層，來應用在N719染料敏化太陽能電池上。其中HD的元件開路電壓 (VOC) 會比一般的奈米粒 (NP) 來的高，在薄膜厚度為28微米的HD元件轉換效率可以得到10.2 %，而一般的NP元件薄膜厚度只能做到18-20微米，其轉換效率可以得到9.6 %。我們利用瞬態光電與電荷萃取量測來得知HD元件擁有較快的電子傳輸能力與較高的電壓特性，所以HD元件相對於NP元件，會表現出較好的效能。 在另一方面，我們一樣以TTIP作為前驅物，用兩歩驟膠溶/水熱過程來製備二氧化鈦，利用不同的添加物，如乙二胺(EDA)、三嵌段共聚物PEO106-PPO70-PEO106 (F127) 、 溴化十六烷基三甲銨 (CTAB)、油酸 (OA)、 TEOA，來控制異相成長的一維結構，得到一系列共八種不同尺寸及形貌的奈米棒 (NR、SR、LR250、LR500、LR1000、CR250、CR500、CR1000) 並說明大的奈米棒 (LR) 的生成機制。以LR250作為鈣鈦礦太陽能電池 (PSC) 的光陽極骨架，以碘化甲基銨鉛 (CH3NH3PbI3) 為敏化劑，以2,2',7,7'-四[N,N-二(4-甲氧基苯基)氨基]-9,9'-螺二芴 (spiro-MeOTAD) 為電動傳輸材料 (HTM)，所製成的元件效率在模擬AM 1.5G之一個太陽照度下可得到12.2 %，其短路電流 (JSC) 為19.21 mA/cm2 、 VOC為887 mV、填充因子 (FF) 為 0.716。我們以吸收光譜、穿透度量測、瞬態光電與電荷萃取量測來說明LR長度對JSC與VOC之影響。

A simple hydrothermal method with titanium tetraisopropoxide (TTIP) as a precursor and triethanolamine (TEOA) as a chelating agent enabled growth, in the presence of a base (diethylamine, DEA), of anatase titania nanocrystals (HD1-HD5) of controlled size. DEA played a key role to expedite this growth, for which a biphasic crystal-growth mechanism is proposed. The produced single crystals of titania show octahedron-like morphology with sizes in a broad range 30-400 nm; a typical, extra large, octahedral single crystal (HD5) of length 410 nm and width 260 nm was obtained after repeating a sequential hydrothermal treatment using HD3 and then HD4 as a seed crystal. The nanocrystals of size ~30 nm (HD1) and of size ~300 nm (HD5) served as active layer and scattering layer, respectively, to fabricate N719-sensitized solar cells. These HD devices showed greater VOC than devices of conventional nanoparticle (NP) type; the overall device performance of HD attained efficiency 10.2 % of power conversion at total film thickness 28 µm, which is superior to that of a NP-based reference device (η = 9.6 %) optimized at total film thickness 18-20 µm. According to results obtained from transient photoelectric and charge-extraction measurements, this superior performance of HD devices relative to their NP counterparts is due to the more rapid electron transport and greater TiO2 potential. In the other hand, a two-step peptization/hydrothermal processes by using TTIP as a precursor with varied additives, ethylenediamine (EDA), triblock copolymer PEO106-PPO70-PEO106 (F127), cetyltrimethylammonium bromide (CTAB), oleic acid (OA) and TEOA, to control the anisotropic growth of the 1D nanostructures, to propose the formation mechanism of large-nanorods and to synthesize the eight kinds of nanorods for different sizes and morphologies. In the perovskite solar cells (PSCs), report a highly efficient of 12.2 % based on anatase TiO2 large-nanorods (LR250) scaffold with lead iodide perovskite (CH3NH3PbI3) as a sensitizer. Infiltration of spiro-MeOTAD hole transport material (HTM) into the LR250/ CH3NH3PbI3 film demonstrated JSC of 19.21 mA/cm2, VOC of 887 mV, and FF of 0.716 under the simulated AM 1.5G one sun illumination. Photovoltaic performance was dependent on the length of the large-nanorods demonstrated by absorption spectra, transmittance, transient photoelectric and charge-extraction measurements.