9:00 AM - EN17.13.02
Robust Perovskite Single Crystal Devices for Efficient Gamma-Ray Detection
Jeremy Tisdale1,Michael Yoho1,Shreetu Shrestha1,Kasun Fernando1,Sergei Tretiak1,Duc Vo1,Wanyi Nie1
Los Alamos National Laboratory1
Gamma-ray detection and spectroscopy is the quantitative analysis of gamma energy spectra, and is of critical importance in many applications, such as nuclear safeguards, nuclear forensics, and many more. Recently, single-crystalline, hybrid (and inorganic) perovskites have been proposed as new semiconducting materials for gamma-ray spectroscopy. In just a few short years, early reports have shown promising results for perovskite-based semiconductor gamma detectors. Some of the most impactful results in this new application for perovskite materials include: CsPbBr3 showing gamma-ray spectra with a resolution of 3.8% at room temperature for a 662 keV 137Cs source at room temperature,1 MAPbI3 showing gamma-ray spectra with a resolution of 6.8% at a lower temperature of 2 °C for a 122 keV 57Co source,2 and MAPbBr2.94Cl0.06 showing gamma-ray spectra with a typical resolution of 12% for a 662 keV 137Cs at room temperature.3 Although first reports for this class of materials have shown significant results with high-resolution gamma detectors, many new issues have arisen for this new application of radiation sensing.
High electric field device stability and ion migration are deeply explored to understand the effects of high bias applications in hybrid perovskites and ways to suppress/eliminate the negative effects towards high-resolution, room temperature gamma-spectroscopy. In a Cr/MAPbBr2.85Cl0.15/Cr device, low electric fields (≤25 V/mm) pulses with extremely low rise times (average of 30 to 65 µs). In order to increase the rise time, the device needs to be operated at higher electric fields, (≥ 50 V/mm) which increases the rise time to an average of 15 µs. However, at high electric fields, the signals become noisy in roughly 10 seconds to 1 minute. We directly probed the cause of the noise using long-term high voltage biasing, while studying the hysteretic behavior via IV characteristics. A new Cr/MAPbBr2.85Cl0.15/Cr exhibits pure Ohmic behavior with negligible hysteresis between -200 to +200 V (E = 100 V/mm). However, after biasing the device for only 10 minutes at +200 V, a large hysteresis loop is observed. After letting the device rest in the dark for two days, the hysteresis loop becomes even larger, rather than restoring to its original properties, showing that the interfacial damage caused is non-reversible. Using the same electrodes in the device architecture allows us to use a technique termed voltage cycling to avoid permanent interfacial damage while operating the detectors. The signals from positive and negative polarity are roughly the same in the metal/semiconductor/metal device. Therefore, when noise appears, we are able to switch polarity to eliminate the noise and continue counting for gamma spectra. Cooling the detector to temperatures of -30 °C further increases the speed of the detector pulses by about 30%. However, the standard deviation in the pulse heights and rise times are still quite large, resulting in low resolution for the detectors with about 30-35% resolution for 59.6 keV γ-rays and 20-25% resolution for 662 keV γ-rays. Further development in hybrid (or non-hybrid) perovskite materials, such as CsPbBr3 and MAPbI3, should prove beneficial, as they are more stable under high electric fields required to achieve high resolution γ-ray spectroscopy. Also, further development in areas such as interfacial engineering and pixelated detector designs will be the next required steps in investigating the improvement for single crystalline, perovskite radiation detectors.
1. He, Y., et al., High spectral resolution of gamma-rays at room temperature by perovskite CsPbBr3 single crystals. Nature Communications, 2018. 9(1), 1609.
2. He, Y., et al., Resolving the Energy of γ-Ray Photons with MAPbI3 Single Crystals. ACS Photonics, 2018. 5(10), 4132-4138.
3. Wei, H., et al., Dopant compensation in alloyed CH3NH3PbBr3−xClx perovskite single crystals for gamma-ray spectroscopy. Nature Materials, 2017. 16, 826.