- 學位論文
用於光電應用的二維鈣鈦礦的設計和特性
Design and Characterization of Two-Dimensional Perovskites for Optoelectronic Applications
摘要
二維（2D）混合有機-無機鹵化鈣鈦礦逐漸成為具有基礎和技術利益的光伏和光電子材料類別。作為一種相對較新的材料，2D鈣鈦礦仍然具有許多尚不為人所知的特性，因此有很多研究工作需要解決，例如光激發後的物種是自由載體還是激子，以及它們如何相互作用和重組。 本文主要對二維鈣鈦礦的合成，特性進行了簡要介紹。隨之，藉由飛秒瞬態吸收光譜法來研究光激發後的激子動力學、侷限效應以及利用電調製光譜法來了解對於施加電場激發態動力學的影響進行了詳細的研究。 本文的第一部分的研究內容包含電場效用對2D薄膜鈣鈦礦（（C4H9NH3）2Pbl4）的吸收、光致發光（PL）光譜和螢光生命期的影響。在斯塔克位移假設下，利用施加電場吸收光譜（電吸收光譜）分析了室溫及45 K的低溫下，電場對其之影響。然而在施加電場光致發光光譜電場（電致發光光譜）的研究中顯示，此化合物通過施加電場後，螢光會焠滅。電場效應對螢光衰變曲線的結果中顯示，焠滅既是由於發光態的數目減少，也是由於場致壽命的縮短。 本文的第二部分探討光致發光對激發功率的依賴性以及外部電場對二維鈣鈦礦薄膜的影響。在過程中，我們觀察到較小的激發功率對熱激子的離解產生自由載流子的效率有增強的效應，因此我們想到了一個機制。結果揭示了二維鈣鈦礦材料在低光度的光伏設備的應用性，例如室內光伏應用。 除了電調製光譜研究以外，我們還使用泵探針光譜(pump-probe spectroscopy)研究了室溫下，具有不同有機陽離子的鈣鈦礦中激子的動力學。有機陽離子對激子動力學的局限效應結果指出自陷激子(self- trapped exciton)的形成取決於有機陽離子的選擇。
並列摘要
Two-dimensional (2D) hybrid organo−inorganic halide perovskites are emerging as promising classes of materials for photovoltaics and optoelectronics with both fundamental and technological interests. As a relatively new material, the 2D perovskites still have many properties that are not well understood, and a lot of research work is necessary to address the question like whether the photo-excited species are free carriers or excitons, and how they interact and recombine. In this thesis, the author presents a brief introduction about two-dimensional perovskite, synthesis and characterization. Along with this, detailed studies on carrier dynamics following photoexcitation, confinement effect by femtosecond transient absorption spectroscopy, and the influence of applied electric field on excited-state dynamics by electromodulation spectroscopy are studied. The first part of this thesis includes electric field effect on absorption, photoluminescence (PL) spectra and on PL decay profile of 2D perovskite thin films, ((C4H9NH3)2Pbl4). Electric-field-effect on absorption spectra (Electroabsorption spectra) observed at room temperature and at a low temperature of 45 K were analyzed by assuming the Stark shift. Electric field effect on photoluminescence spectra (Electrophotoluminescence spectra) of this compound shows PL quenching by the application of the electric field. Field effects on PL decay profiles show that the quenching results both from the decrease of the population of the emitting state and from the field-induced lifetime shortening. The second part of this thesis includes the discussion on the dependence of photoluminescence on excitation power and the effect of an external electric field on 2D perovskite thin-film. We observed that the efficiency of dissociation of hot excitons to produce free carriers was enhanced with a small excitation power, and we came up with a mechanism. The results shed light on the applications of 2D perovskite materials in photovoltaic devices with dim radiation, for example, indoor PV applications. Aside from the electromodulation spectroscopic studies, we studied the dynamics of excitons in perovskite with different organic cations at room temperature using pump-probe spectroscopy. Confinement effect of organic cations on exciton dynamics indicates that the formation of self- trapped exciton depends upon the choice of an organic cation.
參考文獻
延伸閱讀
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