X-ray Scintillation in Lead Halide Perovskite Crystals

www.nature.com/scientificreports OPEN X-ray Scintillation in Lead Halide Perovskite Crystals M. D. Birowosuto1,2, D. Cortecchia3,4, W. Drozdowski5, K. Brylew5, W. Lachmanski5, A. Bruno4 & C. Soci2,4,6 received: 18 August 2016 accepted: 26 October 2016 Published: 16 November 2016 Current technologies for X-ray detection rely on scintillation from expensive inorganic crystals grown at high-temperature, which so far has hindered the development of large-area scintillator arrays. Thanks to the presence of heavy atoms, solution-grown hybrid lead halide perovskite single crystals exhibit short X-ray absorption length and excellent detection efficiency. Here we compare X-ray scintillator characteristics of three-dimensional (3D) MAPbI3 and MAPbBr3 and two-dimensional (2D) (EDBE)PbCl4 hybrid perovskite crystals. X-ray excited thermoluminescence measurements indicate the absence of deep traps and a very small density of shallow trap states, which lessens after-glow effects. All perovskite single crystals exhibit high X-ray excited luminescence yields of >120,000 photons/MeV at low temperature. Although thermal quenching is significant at room temperature, the large exciton binding energy of 2D (EDBE)PbCl4 significantly reduces thermal effects compared to 3D perovskites, and moderate light yield of 9,000 photons/MeV can be achieved even at room temperature. This highlights the potential of 2D metal halide perovskites for large-area and low-cost scintillator devices for medical, security and scientific applications. The investigation of X-ray detectors started with the discovery of X-rays by Wilhelm Röntgen, who noticed the glow from a barium platino-cyanide screen placed besides a vacuum tube1,2. Since this discovery, more than one hundred years ago, the development of efficient3–5 and large-area5–7 X-ray detectors has been a topic of continuous interest, targeting a wide range of applications, from crystallography8 to space exploration9. Modern X-ray detectors rely on two main mechanisms of energy conversion. The first is photon-to-current conversion, in which a semiconducting material directly converts the incoming radiation into electrical current4–6; the second is X-ray to UV-visible photon down-conversion, in which a scintillator material is coupled to a sensitive photodetector operating at lower photon energies2. Both methods are equally compelling for practical implementations, although their viability will ultimately depend on the development of new materials to overcome some of the current limitations, such as high cost, small area, and low conversion efficiency of the X-ray absorbers. Recent demonstrations of the use of hybrid metal-halide perovskites for X- and γ-ray detection has spurred great interest in this class of materials7,10–12. Besides their good detection efficiency, solution processing holds great promise for facile integration and development of industrial and biomedical applications. Methylammonium lead trihalide perovskites (MAPbX3 where MA =  CH3NH3 and X = I, Br, or Cl) have demonstrated excellent performance in optoelectronic devices like field effect transistors13, highly sensitive photodetectors for visible region14, and light emitting devices15,16. Moreover, compositional tuning was used to realize tunable-wavelength lasers17. As X-ray detectors, MAPbX3 yield notably large X-ray absorption cross section due to large atomic numbers of the heavy Pb and I, Br, Cl atoms10,11. Thin-film MAPbX3 p-i-n photodiode and lateral photoconductor devices have shown good efficiency for X-ray photon-to-current conversion10,11. However, thin-film X-ray detectors have typically low responsivity at high (keV) photon energies, where the absorption length (~mm) is much larger than the film thickness (~μm); even if thickness is increased to improve detection probability, direct photon-to-current conversion is ultimately hampered by the limited carrier-diffusion length 1 CINTRA UMI CNRS/NTU/THALES 3288, Research Techno Plaza, 50 Nanyang Drive, Border X Block, Level 6, 637553 Singapore. 2Center of Disruptive Photonic Technologies, TPI, SPMS, Nanyang Technological University, 21 Nanyang Link, 637371 Singapore. 3Interdisciplinary Graduate School, Nanyang Technological University, 639798 Singapore. 4 Energy Research Institute @ NTU (ERI@N), Research Techno Plaza, Nanyang Technological University, 50 Nanyang Drive, 637553 Singapore. 5Institute of Physics, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University, Grudziadzka 5, 87-100 Torun, Poland. 6School of Physical and Mathematical Sciences, Division of Physics and Applied Physics, Nanyang Technological University, 21 Nanyang Link, 637371 Singapore. Correspondence and requests for materials should be addressed to M.D.B. (email: ) or C.S. (email: csoci@ntu. edu.sg) Scientific Reports | 6:37254 | DOI: 10.1038/srep37254 1 www.nature.com/scientificreports/ (~1 μm in perovskites)10. Efficient X-ray photon-to-current conversion has been shown recently in single-crystal (thick) perovskite MAPbBr3, but sensitivity is still limited to energies up to 50 keV11. Also, standard γ-photon counting for energies up to 662 keV has been demonstrated in MAPbI312. As opposed to direct photon-to-current conversion detectors, X-ray scintillators do not suffer from limited carrier diffusion length of the absorbing material18,19. Thin films of phenethylammonium lead bromide, PhE-PbBr4, with sub-nanosecond scintillation decay time have been previously tested in X-ray20 and proton21 scintillators, but yielded only 5–6% detection efficiency of 60 keV X-rays, limited by the film thickness (200 μm)21. By combining the good high-energy response with large absorption cross section deriving from large thickness and high mass-density, single crystal perovskite scintillators are therefore expected to improve detection efficiency of keV X- or γ-rays. In this paper, we present a thorough comparative study of the scintillation properties of three-dimensional (3D) and two-dimensional (2D) low-bandgap perovskite single crystals. We have synthesized mm-scale 3D perovskite crystals MAPbI3 and MAPbBr3, and 2D perovskite crystal (EDBE)PbCl4 (EDBE =  2,2′-(ethylenedioxy)bis(ethylammonium)), comprising of alternating organic and inorganic layers which form a multi-quantum-well-like structure. The excellent quality of these crystals is indicated by structural analysis and by the very small density of shallow traps (n0 ~ 105–107 cm−3, E ~ 10–90 meV) determined by X-ray excited thermoluminescence, which reduces after-glow effects. Thanks to their lower bandgap compared to traditional scintillator crystals6, perovskite crystals produce extremely high light yields of >120,000 photons/MeV (as estimated from X-ray-excited luminescence) at low temperature. In 3D perovskites, the light yield is greatly reduced at room temperature (<1,000 photons/MeV) due to strong thermal quenching effects. Conversely, the 2D perovskite crystal is far more robust (...truncated)