Synthesis, Crystal Growth, and Optoelectronic Characterization of Inorganic Halide Perovskites as Semiconductors for Hard Radiation Detection

McCall, Kyle Matthew

doi:https://doi.org/10.21985/n2-4ty8-0269

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Synthesis, Crystal Growth, and Optoelectronic Characterization of Inorganic Halide Perovskites as Semiconductors for Hard Radiation Detection

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The halide perovskites AMX3 (A = large cation, B = Sn or Pb, and X = halide) have been the subject of intense investigation due to their outstanding optical and electronic properties, which have enabled high solar cell efficiencies thanks to a beneficial electronic structure and long charge carrier lifetimes. One understudied application for these materials is in the field of high-energy radiation detection, which currently is limited to a few semiconductors with inherent difficulties in growth or performance that have thus far limited widespread application. This thesis explores the inorganic halide perovskites (due to their increased stability relative to the organic-inorganic hybrid perovskites) and related compounds for applications in radiation detection. Single crystals of alternative halide perovskites are grown and the optoelectronic and charge transport properties are characterized. This work begins with the investigation of the A3M2I9 (A = Cs, Rb; M = Bi, Sb) defect perovskites, which show response to alpha particle radiation but have limited charge transport due to low mobilities. These low mobilities appear to result from self-trapped excitons in the A3M2I9 compounds identified by steady-state photoluminescence measurements. As an extension of this structural family, halide mixing was attempted to enhance the dimensionality of the 0D Cs3Bi2I9 to the 2D defect perovskite structure, resulting in the new compound Cs3Bi2I6Cl3. However, Cs3Bi2I6Cl3 also exhibits self-trapped exciton luminescence with an increased electron-phonon coupling and therefore had no response even to 405 nm laser. This prompts a return to three-dimensional halide perovskites, as an exhaustive effort is made to find new double perovskites with mixed metals on the M site to yield the formula A2M+M3+X6. The only new compounds of this type which formed were the mixed-valent CsInX3 (X = Br, Cl) which have a unique structure type but prove unstable in ambient conditions and thus are not suitable for radiation detection. Transient reflection and time-resolved photoluminescence measurements are made comparing the Cs3M2I9 compounds with the 3D perovskite CsPbBr3, and show that non- radiative recombination dominates the Cs3M2I9 compounds at room temperature and intrinsically limits the obtainable radiation detector performance, in contrast to the shallow free exciton of CsPbBr3. The defect characterization of CsPbBr3 using photoluminescence and photocurrent spectroscopies is described, and in conjunction with an asymmetric device structure CsPbBr3 is able to achieve high resolution of gamma radiation photopeaks (energy resolution <5 %) for the first time among halide perovskites. The importance of dimensionality and excitonic effects is emphasized throughout this thesis, and these results will guide future development of perovskite detectors towards widespread application.

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