鈣鈦礦奈米晶體在外加電場效應下之吸收與光致發光之研究

Abstract

於本論文中，將藉由電場引致吸收光譜(Electro-absorption measurement) 與電場引致發光與緩解光譜(Electro-photoluminescence and decay measurement) 針對有機鈣鈦礦材料在外加電場效應下之激發態緩解機制作一系列的探討。 第一部分為探討改變鈣鈦礦之溴含量(MAPbI3-xBrx,x= 0,1,2,3)在外加電場效應下之吸收光譜的變化。藉由改變鈣鈦礦的溴含量，鈣鈦礦材料的吸收光譜、能隙和晶向性會有很大的變化。史塔克效應 (Stark effect)詳細的描述物質在外加電場下電子能階的變化過程，並藉由此理論我們可以用來分析物質激發態與基態的偶極矩和極化率變化。在此實驗的分析中，我們對電場引致吸收光譜進行二次積分，從積分後的光譜中我們可以再次確認激子(exciton)在吸收光譜中的形狀與位置。含溴鈣鈦礦太陽能電池效率表現在此章節也有進行測試並將結果與光譜結果進行比較與討論。 第二部分我們利用場效應下之光致發光光譜與激發態緩解光譜對單一鈣鈦礦材料(MAPbBr3)進行探討。在鈣鈦礦太陽能電池材料中，FTO與ITO玻璃皆能被用作太陽能電池的基板，而FTO與ITO電子能階大約位於含溴鈣鈦礦能隙的中間位置。在沒有額外載子傳輸的材料結構下，載子難以從吸光材料傳遞至FTO或ITO中。在此章節將會呈現改變不同的基板製作樣品，利用電場效應下之發光與緩解光譜了解其中的變化。

Hybrid organic-inorganic perovskites have emerged as highly promising materials for the applications in photovoltaic devices, lasers, light-emitting diodes, photodetectors and so on. The charge transport properties and the responses of charge to an externally applied electric field is an important basic property of semiconductors and other materials, and are critically important with regard to their uses in optoelectronic devices. It is known that the energy of the electronic states is shifted by the application of electric field, depending on the magnitude of electric dipole moment and molecular polarizability, and in the result the photoexcitation dynamics is affected by electric field. Such field effects on photoexcited dynamics can be examined with electroabsorption (E-A) and electrophotoluminescence (E-PL) spectroscopy. In the first part, we have examined the electric field effects on absorption of MAPbI3, MAPbI2Br, MAPbIBr2 and MAPbBr3 thin films. These thin films were developed on an indium-tin-oxide (ITO) coated quartz substrate by a spin-coating method from the n-methyl-2-pyrrolidone (NMP) solution of a mixture of MAI and PbI2, MABr and PbI2, MAI and PbBr2, and MABr and PbBr2, respectively. ITO and Ag films were served as electrodes for E-A measurements. The integral analysis method is use to analyze the E-A spectra, therefore the exciton peak in absorption spectrum can be confirmed. Under the theory of stark effect, the change in dipole moment and polarizability can be determined. In the second part, the E-PL and field-induced PL decay measurement have been examined on MAPbBr3 thin film spin coated on FTO or ITO substrate. The F-doped tin oxide (FTO) and indium tin oxide (ITO) substrate both can be used in perovskite solar cell. The energy state of FTO and ITO substrate are -4.4eV and -4.7eV, respectively, which compare to the energy state of MAPbBr3, their positions are around at the middle of band gap of MAPbBr3. Without any carrier transporting layer, it might be difficult to transport the electron (hole) from light harvesting layer to the ITO or FTO substrate. In this part, the sample structure, as shown in section 3.1.3, by changing the substrate from FTO and ITO substrate, E-PL and field-induced PL decay measurement will be examined.