臺灣博碩士論文加值系統

近年來，有機-無機混成鈣鈦礦因其優異的光學及電學性質受到廣泛的關注及研究，儘管其熱穩定性及大氣穩定性仍有待改進。二維層狀鈣鈦礦因其對水氣及熱擁有較佳的耐受性，近來被視為改善此問題之良好方案。其中，理論研究報導在鈣鈦礦晶格中引入硫氰酸根離子以取代原本的鹵素離子可大幅提升其大氣穩定性，增加了鈣鈦礦實際應用的可能性。然而，唯一被廣泛討論的MA2Pb(SCN)2I2隨後在實際元件應用上的穩定性仍然有限。因此，本論文藉離子替換探討一系列二維硫氰酸根鈣鈦礦A2Pb(SCN)2X2（A=甲脒基、甲基胺基、銫離子，X = 溴離子、碘離子）之結構穩定性。當較小的銫離子置於鈣鈦礦晶格時，整體鈣鈦礦結構因較輕微的晶格扭曲而較甲基銨基形成之結構穩定，且擁有較為優異的光響應特質。此外，一系列混合鹵素之鈣鈦礦Cs2Pb(SCN)2(I1-xBrx)2 (x = 1/3, 1/2, 2/3, 1)亦被證明其較純碘(x=0) 鈣鈦礦優異的穩定性，其薄膜顏色亦可透過鹵素調控呈現各式鮮豔色彩。純溴離子組成之Cs2Pb(SCN)2Br2 則為此系列最為穩定之鈣鈦礦，透過吸收圖譜證實超過72小時仍維持穩定之結構。
Cs2Pb(SCN)2Br2 優異的穩定性及光學性質，結合了石墨烯優良的載子遷移率，被應用於石墨烯-鈣鈦礦複合結構之電晶體式光感測器。元件受益於妥善配置的能級、迅速的載子分離而擁有高光響應度(9.51 x 105 A W−1)及快速的響應時間(1.82 s)。除了探究單層結構的硫氰酸基鈣鈦礦，我們試著利用傳統的旋轉塗佈製程探索多層結構的硫氰酸碘鈣鈦礦及硫氰酸溴鈣鈦礦之可能性。所得之均勻薄膜透過X光繞射、吸收光譜、螢光放射光譜檢視，卻可見明顯的相分離情形，證明所製備的薄膜為僅為單層二維鈣鈦礦及立體鈣鈦礦之混合物。為了嘗試其他偽鹵素置換鹵素於硫氰酸基蓋鈦礦結構之可能性，我們另外使用了與碘離子大小相近的氟硼酸根於結構中。然而，所使用的硼氟化鉛之水溶液性質增加了其配置前驅溶液的困難性，無論使用水及二甲基甲醯胺作為前驅溶液之溶劑均無法得到均質之溶液。我們進而將其析出之透明晶體及清澈溶液部分於乾燥處理後，利用粉末X光繞射檢視其結構組成，藉由與初始物比對圖譜，我們發現所得產物為不同比例之初始物混合物，證明製備二維氟硼酸鈣鈦礦之嘗試失敗。本論文成功展示一系列嶄新的二維硫氰酸鈣鈦礦Cs2Pb(SCN)2(I1-xBrx)2 (x = 0, 1/3, 1/2, 2/3, 1)，亦藉由石墨烯-鈣鈦礦混合結構之光感測電晶體證明其實際應用的潛力。惟他種偽鹵素鈣鈦礦仍須更進一步之研究。

Organic-inorganic hybrid perovskites have attracted wide research interest for their figure of merit toward practical applications, including the superior optical and electronic properties. Nevertheless, both thermal and ambient stabilities await significant improvement. Two dimensional (2D) layered perovskites were lately reported to offer a solution to thermal/moisture vulnerability. Among these rising 2D perovskites, introducing thiocyanate anion (SCN-) to replace halides in the perovskite lattice was verified to effectively enhance the structural stability through theoretical study. However, the experimental investigation aroused concern about ambient stability of (MA)2Pb(SCN)2I2 (MA=CH3NH3+), the only intensely investigated SCN-based perovskite, thus cast a shadow over its potential in further application. In this thesis, we first conducted systematical engineering to the SCN-based perovskites, A2Pb(SCN)2X2 (where A = MA+, Cs+, FA+, X = I- or Br-), and revealed the critical limitation to its constituent ions imposed by linear SCN anion. We demonstrated the smaller Cs+ is a favorable cation choice comparing to MA+ because of the trifling structure torsion and that Cs2Pb(SCN)2I2 also possess better photo response in comparison with MA2Pb(SCN)2I2. Moreover, a series of all inorganic mixed halide perovskites Cs2Pb(SCN)2(I1-xBrx)2 (x = 1/3, 1/2, 2/3, 1) with vivid color, was testified to retain better ambient stability than Cs2Pb(SCN)2I2. Also, when Br fully substituted I, the structure was suggested to have the best stability toward real-time stability test conducted for 72 hr.
The advantage of Cs2Pb(SCN)2Br2 with best stability and excellent photons absorption capability, amalgamated with that of graphene with outstanding carrier mobility, was exploited next in a graphene-perovskite hybrid photodetector. The device achieved an outstanding responsivity of 9.52 × 105 A W−1 decent response rise time of 1.86 s with the assistance of the appropriate energy level alignment and rapid charge separation benefit from the built-in electrical field. Other than the exploration on monolayer SCN-based perovskite, the one with multi-layer 2D framework were also investigated through traditional solution-processing approach in both I and Br system. The attempt was proved to be too reckless since the resultant XRD and optical spectra revealed the spin-coated film was composed by mixed phase of single layer SCN perovskites and 3D perovskites of the existed component. To further achieve the pseudohalide-based perovskite, we utilized another pseudo halogen, tetrafluoroborate (BF4-), to formulate the perovskite lattice as the strategy in SCN-based perovskites beause of its similar spatial size with iodide. The dilemma in BF4-based perovskite is the difficulty in processing precursor in that no plausible solvent was able to dissolve the raw materials. The XRD measurement of both precipitate and dried solution was used to examined the constituent in the obtained substance, yet unfortunately to be a mixture of raw materials. In the thesis, we demonstrated a novel series of 2D Cs2Pb(SCN)2(I1-xBrx)2 (x = 0, 1/3, 1/2, 2/3, 1) and verified their practical application in graphene-perovskite hybrid photodetector, yet the validation of another pseudohalide-based perovskite still demand further research effort.

誌謝………………………………………………………………………………………i
摘要……………………………………………………………………………………...ii
Abstract………………………………………………………………………….............iv
Contents
Table Captions
Figure Captions
Chapter 1. Introduction 1
1.1 Introduction to perovskites 1
1.1.1 Two dimensional (2D) perovskites 1
1.1.2 Pseudo halide perovskites 2
1.2 Photoluminescence mechanism 3
1.2.1 Fluorescence and Phosphorescence 3
1.2.2 Jablonski diagram 4
1.3 Introduction to perovskite photodetectors (PDs) 5
1.3.1 Device structure of photodetectors 5
1.3.2 Graphene-perovskite hybrid PDs 6
1.3.3 Principle operation of hybrid PDs 6
1.3.4 Figure of merits for characterizing PDs 7
1.4 Research Objectives 8
Chapter 2. Stable, Color-Tunable 2D SCN-Based Perovskites: Revealing the Critical Influence of Asymmetric Pseudo-Halide on Constituent Ions 15
2. 1 Introduction 15
2.2 Experiment Section 18
2.2.1 Materials 18
2.2.2 Characterization 19
2.2.3 Device Fabrication and Characterization 20
2.3 Results and discussion 20
2.3.1 Crystal Characterization of A2Pb(SCN)2I2 (A = FA+, MA+, and Cs+) 20
2.3.2 Optical properties of (MA)2Pb(SCN)2I2 and Cs2Pb(SCN)2I2 22
2.3.3 Fabrication and Characterization of Cs2Pb(SCN)2(IxBr1-x)2 26
2.4 Conclusion 29
Chapter 3. Graphene-perovskite hybrid photodetectors with HBC-6ImBr surface modification utilizing 2D Cs2Pb(SCN)2Br2 38
3.1 Introduction 38
3.2 Experiment Section 40
3.2.1 Materials 40
3.2.2 Characterization 40
3.2.3 Device Fabrication and Characterization 41
3.3 Results and discussion 42
3.3.1 Structure design of Graphene-Cs2Pb(SCN)2Br2 photodetector 42
3.3.2 Electronic properties of 2D perovskite Cs2Pb(SCN)2Br2 and graphene 43
3.3.3 Performance of hybrid graphene-perovskite PDs 45
3.4 Conclusion 48
Chapter 4. Tuning composition in psuedo-halide based perovskite 52
4.1 Introduction 52
4.2 Experimental section 53
4.2.1 Materials 53
4.2.2 Characterization 54
4.3 Results and discussion 54
4.3.1 Multi-layer SCN-based perovskite 54
4.3.2 BF4-based perovskite 56
4.4 Conclusion 58
Chapter 5. Conclusion and future work 61
Reference 63

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