| 摘要: | 本論文是在研究鹵化物鈣鈦礦發光二極體(halide perovskite light emitting diode, PeLED)。近年來鹵化鈣鈦礦材料在光電領域迅速發展，在太陽能電池(solar cells, SCs)領域其光電轉換效率達22%以上，而在發光二極體(light emitting diodes, LEDs)領域，它的外部量子效率可達11%，並有持續上升的趨勢。鹵化物鈣鈦礦本身具有高光致發光效率、單色性、涵蓋可見光範圍的發光波長可調性，可使用溶液製程，降低製程成本，是未來顯示技術的新星。
在發光二極體的應用中，當發光層薄膜內的材料結晶顆粒愈小表示有更佳的輻射複合效率。本論文先使用一般常見的旋轉塗佈併用反溶劑法(anti-solvent method)製程，重現主要參考文獻之結果。此文獻是在MAPbBr3前驅物溶液中加入溴化丁基胺(BABr)界面活性劑(surfactant)，使得鹵化鈣鈦礦在旋轉塗佈的過程中可以自發形成量子點(quantum dot)堆疊的薄膜，此量子點是鹵化物鈣鈦礦晶體外面包覆一層長鏈的界面活性劑，稱表面鈍化(surface passivation)，他們改變界面活性劑的量以降低量子點大小，提升發光效率。
本論文第二部分則是利用鹵化物鈣鈦礦在特定溶劑中的反溶解率(inverse solubility)特性，在旋轉塗佈的過程中，使用雷射來加熱基板，使旋轉塗佈中的薄膜溶液溶解度瞬間下降，在整片薄膜中瞬間誘發成核(nucleation)，成核數量愈多表示薄膜中量子點可成長(growth)的大小將會愈小。雷射加熱對材料的熱穩定性要求較高，所以材料改用全無機的鹵化鈣鈦礦(CsPbBr3)。
實驗第一部分結果得到與參考文獻相同的趨勢，但唯因發光二極體元件電洞傳輸層的設計差異，導致薄膜旋塗均勻性與對電子的阻隔能力較差，得到較低的發光效率，外部量子效率0.5%。第二部份結果顯示在旋轉塗佈中利用溶液的反溶解率特性，使用雷射加熱誘發成核的原理是正確可行的，並且此方法製做的發光二極體的發光強度是第一部份結果的2倍，可見極具發展潛力。;The thesis is research of halide perovskite light-emitting diode(PeLED). Halide perovskites have recently emerged as promising for optoelectronic applications. In the field of the solar cells, its power conversion efficiency had been approached to 22%, and for the light-emitting diodes, its external quantum efficiency can higher than 11%. Halide perovskites are the new star of future display technology, they have the properties of high photoluminescence efficiency, high-colour purity, wide colour tunability and feasibility of solution-processing for low costs.
In the application of light-emitting diodes, the smaller crystalline particles in the light emitting layer have the better radiative recombination efficiency. In the first part of our experiments, we use the spin coating with the anti-solvent method to reproduce the results of the main reference. They add the surfactant of butylammonium bromide (BABr) to the perovskite (MAPbBr3) precursor solution to form a quantum dot stacked film by anti-solvent treatment via spontaneous reaction. The surface of the quantum dot is passivated by the long-chain surfactant, that is called surface passivation. They varied the ratio of BABr and MAPbBr3 to decrease the dot size.
The second part of the experiment is to apply the inverse solubility characteristics of the halide perovskite in a specific solvent. In the process of spin coating, the substrate is heated by a laser to induce nucleation of nano-crystalline in the entire film instantaneously via decreasing the solubility instantly. The more nucleus form, the smaller size of crystalline grow. Laser heating requires a high thermal stability of the material, so the material is replaced with an all-inorganic halide perovskite (CsPbBr3).
We reproduced the same trend as the results of the reference, by varied the amount of surfactant added. However, due to the design difference of the hole transport layer of the light-emitting diode, we got the uniformity film with pinholes and bad electron blocking effect, which is resulting in the external quantum efficiency of 0.5%. The second part of the results shows that the principle of using Laser heating to induce nucleation during spin coating via inverse solubility is correct. The luminance of the LED produced by this method is higher 2 times than the first part of the experiment at the same working voltage, showing its huge development potential. |
