Online program Overview Session: RTSD-05

Abstract

CsPbBr₃ is a perovskite room-temperature semiconductor crystal, with properties for high-resolution gamma-ray detection. This material has been fabricated in large volumes, with detectors up to 12 mm thick demonstrated to remain stable for up to 4 months under continuous bias, achieving energy resolutions of 1.1%-1.6% FWHM at 662 keV. This research employs depth-of-interaction analysis on a 12 mm-thick pixelated detector to investigate how optimizing digital pulse shaping parameters as a function of interaction depth and pixel electrode can improve energy resolution. Rather than applying a uniform set of shaping parameters across all events, each waveform is processed independently, allowing shaping to be tuned to the charge-transport characteristics specific to each depth bin and pixel pair. Two optimization methods are compared: a Linear 1D approach, in which rise time and flat-top time are constrained to be equal, and a Grid 2D approach, in which both parameters are varied independently across a wider search space. Our results show that both depth-dependent methods consistently outperform uniform shaping across all drift times. The 2D grid method achieves lower energy resolution than the 1D method but at a significantly higher computational cost (up to an order of magnitude slower). Using 1D optimization, per-pixel energy-resolution improvements of 4.1% to 15.4% were observed, with a best achieved resolution of 0.65% FWHM at 662 keV for near-pixel-side events, representing an improvement over previously reported thinner detectors while maintaining comparable stability.

Abstract

This paper outlines the technological steps and methods used to manufacture perovskite semiconductor radiation detectors and compares them with those used in the manufacture of other semiconductor materials, such as HPGe, Si, CZT, CdTe, and TlBr. We analyse the problems and limitations arising when implementing these technologies at this early stage of perovskite detector development. We examine and critique the technologies involved in crystal growth and processing; for example, mechanical (cutting, grinding, polishing...), chemical (etching, washing...), contact deposition and patterning (masking, photolithography) as well as the welding of contacts and micro assembly of detector crystals.

Applying the processes described above to CsPbBr₃ crystals of dimensions of 5´5´3 mm³, we have manufactured a number of radiation detectors with different contact architectures - a planar contact structure, a planar structure with a guard ring and a ring-electrode type structure. The detectors provided FWHM energy resolutions of less than 1% at 662 and 1332 keV (0.79% and 0.86%, respectively) with a peak to Compton ratio of 11, The FWHM energy resolutions at 59.5 keV, 122 keV and 5.9 kV were 2.7 keV (4.5%), 3.9 keV (3.2 %) and ≤2.6 keV, respectively.

Abstract

Metal-halide perovskites are promising low-cost semiconductors for photon-counting X-ray imaging. However, their temporal response is often hindered by ion migration induced field screening, which can lead to an underestimation of charge carrier mobility. Here, charge transport is studied in CsPbBr₃ single-crystal detectors using time-of-flight technique and ²⁴¹Am (60 keV) gamma-counting spectroscopy under direct-current (DC) and alternating-current (AC) bias. In DC operation, polarization effects restrict the extracted hole mobility to ~36 cm²V^-1s^-1. Applying AC bias suppresses ionic accumulation and reveals substantially higher hole mobility, reaching up to ~560 cm²V^-1s^-1. Gamma counting under AC operation preserves energy resolution (~10–11%) while accelerating charge collection: the mean response time decreases from ~460 ns (DC) to ~110 ns (AC). These results show that alternating biasing mitigates ion migration induced field distortion and enables perovskite detectors to approach the response speeds required for fast photon counting.

Abstract

State-of-the-art radiation detectors are based on scintillating crystals mechanically coupled to silicon photodetectors, an architecture that limits applicability in terms of size, cost, and form factor. Here we report vapor-deposited thin-film perovskite photodiodes monolithically integrated onto large-area organic scintillating slabs fabricated by a cell-casting approach, combining direct and indirect detection in a single device. The use of transparent conducting oxides (TCOs) deposited by industrial-scale pulsed laser deposition (PLD) enables both substrate- and superstrate-configuration devices. A polystyrene planarization layer is introduced to ensure uniform thin-film device fabrication on the plastic scintillating substrates. Under X-ray irradiation, the hybrid detectors demonstrate an enhanced radiation response compared to bare perovskite photodiodes, providing a proof-of-concept for an inexpensive, scalable radiation detection platform.

Abstract

Solution-grown lead halide perovskites are promising materials for next-generation radiation detectors. Inverse temperature crystallization (ITC) growth is widely used to obtain large crystals within a relatively short time.  However, the rapid increase in supersaturation during heating promotes spontaneous nucleation, leading to compositional inhomogeneity and elevated defect density. To address this limitation, we investigated the growth of MAPbBr₃ single crystals using a slow solvent evaporation-induced crystallization method performed at a controlled, constant temperature near room temperature. X-ray diffraction confirmed the formation of high-quality single crystals with improved crystallinity compared to our standard ITC-grown crystals.   Detectors fabricated in an Au/MAPbBr₃/Cr planar configuration exhibited reduced dark current and enhanced X-ray sensitivity relative to devices based on ITC-grown crystals. These results demonstrate that this growth strategy provides a viable pathway to improved crystal quality and device performance.

Abstract

Low-dose diagnostic X-ray imaging requires detector materials that combine high stopping power, low electronic noise, fine spatial resolution, and stable operation under clinically relevant X-ray energies. Cadmium telluride currently provides this performance in direct-conversion imagers, but its cost and crystal-growth constraints limit scalability. We report direct conversion detectors working in photovoltaic mode based on solution-grown mixed-cation methylammonium-formamidinium lead triiodide single crystals. The crystals were grown with controlled thicknesses up to 1 mm on charge-selective contacts and patterned indium tin oxide arrays. Optical and X-ray detection characterization shows millimeter-scale charge extraction without an externally applied field, with electron mobility-lifetime products up to 0.17 cm² V^-1 and diffusion lengths of 3.5 mm. The devices achieve single-photon sensitivity and detective quantum efficiency above 90% at 60 keV, while the same growth route enables conformal integration into 40 µm-pitch linear arrays with spatial resolution up to 19-line pairs per millimeter. The detectors also maintain a stable response over up to two years of intermittent operation and storage. These results indicate that solution-grown perovskite single crystals can approach cadmium telluride-level low-dose imaging performance while retaining a scalable low-temperature materials platform for medical and industrial X-ray imaging.

Abstract

We present a scalable and calibrated proton dosimetry platform based on flexible 2D perovskite (PEA₂PbBr₄) thin films, enabling high-resolution beam profiling in clinically relevant conditions. The devices consist of solution-processed thin films deposited on 75 µm Kapton substrates and operated as two-terminal coplanar detectors. Their response has been characterized under therapeutic proton beams (70–200 MeV), showing stable operation, good radiation tolerance up to 20 Gy, and a linear dependence of the collected charge on the total dose. The current response exhibits a reproducible sublinear dependence on dose rate, enabling the definition of calibration protocols. The scalability of the technology is demonstrated through multipixel linear arrays composed of up to 28 devices arranged side-by-side, showing good uniformity with pixel-to-pixel variations below 25% in sheet resistance and 15% in calibration parameters. After calibration, the system enables accurate reconstruction of transverse proton beam profiles in agreement with nominal beam shapes. A key feature of these detectors is their angular-independent response (<2% variation up to 90°), which enables operation in an edge-on configuration and a transition from pixel-pitch-limited to thickness-limited spatial resolution. This concept is extended to a stacked pixel-on-pixel multipixel architecture for high-resolution beam profiling (77 µm). Finally, the devices have been validated in an anthropomorphic phantom under clinical 200 MeV proton irradiation, demonstrating the capability to discriminate beam position shifts and reconstruct dose profiles consistently with radiochromic film and commercial dosimetry measurements. These results highlight the potential of flexible 2D perovskite detectors as a versatile platform for scalable, high-resolution, and real-time proton beam dosimetry.

Abstract

Room-temperature direct-conversion X-ray imagers require sensor materials that combine high stopping power, efficient charge transport, spatially confined charge collection, and stable temporal response. We report an all-inorganic perovskite detector platform in which phase purity of cesium lead bromide (CsPbBr₃, CPB) is used as the central materials control parameter. Low-impurity, spectroscopic-grade CPB crystals were produced by purification and optimized Bridgman growth, milled to nanopowder, and blade-coated into dense sensor films on active-pixel readout arrays at temperatures compatible with backplane electronics. X-ray diffraction of both precursor crystals and sensor films showed the stable orthorhombic Pnma phase with characteristic reflections, indicating preservation of phase through crystal-to-powder-to-film conversion. In contrast, unoptimized starting material contained a CsPb₂Br₅ tetragonal secondary phase, generated nonuniform slurries and aggregate-rich films, and produced degraded X-ray images due to interpixel charge sharing. The optimized CPB sensors demonstrated linear response to 30 keV X-rays, sensitivity of 55,400 μC Gy_air⁻¹ cm⁻² at 0.5 V/μm, a limit of detection of 417 pGy_air s⁻¹, and a hole mobility-lifetime product of 8.0 × 10⁻⁴ cm²/V. Phase-pure CPB also produced low residual lag, reducing detector lag from 8.9% to 1.1%, while enabling 6.9 lp/mm at 20% modulation transfer function on a 100 μm-pitch amorphous-silicon array and 20 lp/mm on a fine-pitch CMOS readout. These results identify phase-pure orthorhombic CPB as a scalable room-temperature semiconductor for low-lag, high-sensitivity, high-resolution X-ray imagers.