二維鹵化物鈣鈦礦薄片的製備與特性

Abstract

本次研究我們採用溶液法，先使用水作為溶劑配置Pb(Ac)_2溶液作為前驅物，使用冰箱控制溫度並搭配旋轉塗佈機，成功在二氧化矽基板上生成大量Pb(Ac)_2的薄片晶體，直徑大小多為6~7μm，厚度大部分為10nm左右。接著透過二步法，配置MAI與MABr溶液，將溶液旋塗在Pb(Ac)_2上得到MAPbI_3與MAPbBr_3的鈣鈦礦，接著我們進一步配置PEAI溶液，用旋塗法把溶液塗佈在先前製成的MAPbI_3鈣鈦礦上合成二維鈣鈦礦，使用XRD、Micro PL量測後得到與文獻對應的PL峰值與XRD圖譜，確認有成功將Pb(Ac)_2轉換成鈣鈦礦。在搭配液態氮做變溫量測時，會由於晶格扭曲的原因，溫度越低PL峰值越高，並且會出現紅移的現象，透過阿瑞尼士方程式，我們得到MAPbI_3的激子束縛能E_b=44.07meV，MAPbBr_3的激子束縛能E_b=94.45meV，(PEA)_2 PbI_4的激子束縛能E_b=54.63meV，可以看出鈣鈦礦結構的侷限程度增加會讓E_b增加。同樣透過二步法，我們將掌性長鏈分子R/S-MBABr旋塗在MAPbBr_3鈣鈦礦之上，並用Micro PL搭配左右旋光測試不同掌性的分子對旋光的選擇性，並使用Micro PL量測材料的圓偏振發光(CPL)，並算出兩者各自的發光不對稱因子g_lum，雖然不同片鈣鈦礦晶體所算出的g_lum並不穩定，但(R-MBA)_2 PbI_4所得到的g_lum均小於0，而(S-MBA)_2 PbI_4所得到的g_lum均大於0，意味著(R-MBA)_2 PbI_4的CPL以右旋光為主，(S-MBA)_2 PbI_4的CPL則是左旋光為主，證明透過二步法所製成的掌性鈣鈦礦具有作為旋光材料的潛力。

In this research, we used solution method to make Pb(Ac)_2 for precursor by using DI water for solvent. We used refrigerator to contain the temperature and spin coater to let the solution distribute uniformly on the SiO_2 substrate. The diameter of most of the flakes is 6~7nm, and the thickness of those is about 10nm.Then, we used two-step method to transfer Pb(Ac)_2 to MAPbI_3 and MAPbBr_3. We made MAI and MABr solution and used spin coater to let the solution on the Pb(Ac)_2 and become perovskites. Furthermore, we made PEAI and R/S-MBAI solution to spin on MAPbI_3 to make two-dimensional perovskite and chiral perovskites. By using Micro PL and XRD, we confirmed that we changed Pb(Ac)_2 into perovskites successfully.As we did temperature dependence PL, we can see that the lower temperature is, the higher the PL peak is. The PL peak also redshift when the temperature decrease. By using Arrhenius equation, we got the excitation binding energy of MAPbI_3 is E_b=44.07meV, MAPbBr_3 is E_b=94.45meV, and (PEA)_2 PbI_4 is E_b=54.63meV. The result seems to tell that the restrict space in the perovskite influences E_b.We used two step method to transfer MAPbI_3 to (R/S-MBA)_2 PbI_4. Then we used Micro PL to measure the CPL of chiral 2D perovskites by right-headed or left-headed circularly polarized light and calculated g_lum. Although the chiral perovskites’ g_lum are not steady, we can still find that the CPL of (R-MBA)_2 PbI_4 is right-headed circularly polarized, and the CPL of (S-MBA)_2 PbI_4 is right-headed circularly polarized. The result proves that the chiral 2D perovskites made by two step method can be good chiral optical materials.