Solution-processed lead halide perovskite single crystal scintillators

• Main Author: Xie, Aozhen
• Other Authors: Cuong Dang
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2021
• Subjects: Science::Chemistry
• Online Access: https://hdl.handle.net/10356/146786
• Institution: Nanyang Technological University

Perovskite scintillators have been a rising research topic after the zeal on promoting perovskite solar cell efficiency. Heavy element Pb, low fabrication cost and relatively strong emission make some of perovskite scintillators (like (PEA)2PbBr4 and (BA)2PbBr4 in this thesis) potentially competitive in comparison to current commercial scintillators. In this thesis, the focus will be on the how different components, including organic cation, halide anion and dopant affect the scintillator performance. A series of characterizations were systematically carried out to correlate the perovskites’ properties to their behavior and performance. Based on these characterization results, corresponding conclusions and predictions will be provided. To begin with, we synthesized and characterized 3D perovskite MAPbX3 (X=Cl, Br or I) single crystals that have been well studied in solar cell and optoelectronic areas but relatively new in the scintillator field. My first work (Chapter 4) demonstrated the effect of halide anions on thermal quenching behavior of perovskite under X-ray. The thermal quenching activation energy and the ratio between the thermal quenching rate and the radiative transition rate are decreasing from MAPbCl3 to MAPbI3 in 3D MAPbX3 family. The conclusion could be reasonably extrapolated to 3D perovskites beside methylammonium lead halide perovskites. After mastering the synthesis of 3D perovskite crystals and the related characterization analysis, we further explored the 2D perovskite crystals, which were predicted to be better compared to 3D counterpart. In my second work (Chapter 5), we found that Li doping can enhance the scintillating performance of 2D perovskite (PEA)2PbBr4, such as higher light yield and smaller light yield difference caused by temperature change. In addition, for the first time we utilized the Li dopant strategy to extend the detection energy range by demonstrating the detection of alpha particle and thermal neutron with our Li-doped (PEA)2PbBr4 crystals. With such strategy, there are numerous chances to develop new functionalities based on available perovskite scintillators. Furthermore, we explored the similarities and differences in 2D perovskite crystals made of varied cations and anions as my last work (Chapter 6). We synthesized eleven 2D perovskites with different cations and anions to compare the influence they brought. Bromide perovskite crystals are better over the chloride and iodide ones in terms of high chemical stabilities in ambient as well as their emission wavelengths that match the high quantum efficiency ranges of Si-based detectors. Simple linear alkyl and small bulky ring-containing cations tend to introduce (100) type which typically exhibits narrow emission and more likely to show negative thermal quenching behavior (stronger emission upon higher temperature). Cations containing O and N elements (beside ammonium group) usually lead to (110)-orientated perovskites which show broad emissions in visible light range because of self-trapped excitons. We believe our conclusions in this thesis could shed light on similar scintillator design investigations. At last, based on my experimental skills and knowledge learnt from other perovskite scintillator references, I ended up my thesis with the comparison of 2D and 3D perovskite single crystal scintillators. 3D perovskite scintillators (especially thick crystal samples) are easy to obtain due to early synthesis investigations. This provides a good way to predict, modify and test the properties and performances of 3D perovskite scintillators. Ultimately, we should focus on 2D ones due to their theoretically higher performances although the current synthetic method is inefficient. 2D perovskite single crystal scintillators are potential candidates to compete with current commercial scintillators in the future market.