定電流陽極沉積法製備二氧化鈦薄膜及其應用於鈣鈦礦太陽能電池阻隔層之研究

Preparation of Titanium Dioxide Ultra-thin Film by Galvanostatic Anodic Deposition and Its Application on Blocking Layer for Perovskite Solar Cell

蘇子森(Su, Tzu Sen)

指導教授 ： 衛子健

國立清華大學/工學院/化學工程學系/碩士(2015年)

https://doi.org/10.6843/NTHU.2015.00060

摘要

在鈣鈦礦太陽能電池 (Perovskite solar cell, PSC)中，由於FTO玻璃與電洞傳輸材料(Hole transport material, HTM)間為歐姆接觸(Ohmic comtact)。一旦兩者接觸會就會造成嚴重的載子複合，降低元件光電轉換效率。因此在FTO玻璃和二氧化鈦多孔支架層中間製作一層阻隔層，避免FTO玻璃與HTM直接接觸面積並形成蕭基界面(Schotty contact)，抑制逆向電子傳輸，此為製備高效能鈣鈦礦太陽能電池的必要條件之一。
本研究使用陽極定電流沉積法製備薄且緻密的二氧化鈦(TiO2)阻隔層，藉由調控沉積的電流及電量密度來控制TiO2薄膜的形貌與厚度，並探討阻隔層之材料特性與製備條件對鈣鈦礦電池元件光電化學特性的影響。紫外光可見光光譜顯示TiO2薄膜在製備前後幾乎不影響FTO玻璃的穿透度，顯示薄膜是均勻且非常薄的形態；由場發式電子顯微鏡(FESEM)觀察發現，沉積電流密度會影響二氧化鈦薄膜的微結構；以低電流密度進行沉積時，可得到片狀排列的結晶，提高電流密度後則得到顆粒堆疊的結構。此超薄的TiO2薄膜以二次飛行質譜儀(TOF-SIMS)及循環伏安法(CV)檢測後得知，即使TiO2阻隔層的厚度低於30nm但其依舊表現出良好的抑制再結合效果，證實了電沉積TiO2阻隔層具有薄又緻密的優勢。
目前的實驗結果顯示，最適化電沉積阻隔層條件為電流密度20μA/cm2，且電量密度10mC/cm2時，厚度為13.5奈米。循環伏安檢測中發現，相較於常用的旋轉塗佈法，電沉積TiO2阻隔層的薄膜孔隙度約為旋轉塗佈阻隔層的0.7倍，且搭配電沉積阻隔層的最佳元件效率為13.6%，明顯高於旋轉塗佈法之阻隔層元件效率的10.4%。其主要改進在短路電流(JSC)與填充因子(FF)部分，顯示電沉積阻隔層的緻密性能有效抑制FTO界面的再結合反應，提升電子收集效率。

關鍵字

鈣鈦礦太陽能電池 ； 阻隔層 ； 二氧化鈦 ； 定電流陽極沉積法

並列摘要

In perovskite solar cells (PSC), the fluorine-doped tin oxide (FTO) glass and hole transport material (HTM) form ohmic contacts, which lead to recombination of charge carriers and consequently reducing the cell performance seriously. The recombination is effectively reduced via introducing a blocking layer (BL) between FTO glass and titanium dioxide (TiO2) mesoporous layer, which eliminates the contact between FTO and HTM, and results in suppressing the recombination between electrons in FTO and holes in HTM. Therefore, preventing the recombination from direct contact between FTO and HTM layer is crucial for high efficiency PSC.
In this study, an ultra-thin and compact TiO2 BL on FTO glass was prepared by galvanostatic anodic deposition. This electrodeposition (ED) method can control the morphologies and thicknesses of TiO2 film by manipulating the current density and coulomb density. The material properties of BLs preparimg by various deposition conditions and their photoelectrochemical performances were also scrutinized.
Ultraviolet -Visible Spectrometer (UV-Vis) spectra show that the transmittance of FTO substrate is not affected by the ED-BL. FESEM (Field emission scanning electron microscope) images reveal that the structure of the TiO2 film is affected by the depositing current density. As the current density increases, the particle size became smaller. Evidenced by TOF-SIMS (Time-of-flight secondary ion mass spectrometer) and CV (Cyclic voltammogram), it is proved that the interfacial recombination is profoundly suppressed by ED-BL.
Comparing to the commonly used spin coating (SC) method to deposit BL, our study shows that the high quality BL can effectively enhance the performance of perovskite solar cell especially at short circuit current density JSC (mA/cm2) and fill factor FF via decreasing the electrons loss from FTO glass to HTM effectively. As a result, current collection efficiency was enhanced at FTO electrode. The best perovskite cell with ED-BL achieved a higher power conversion efficiency of 13.6% that is higher than SC-BL one of 10.4% by approximately 30%.

並列關鍵字

Perovskite solar cell ； Blocking layer ； Titanium dioxide ； Galvanostatic anodic deposition

參考文獻

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