Speaker
Description
The deployment of metal halide perovskites (MHPs) in radiation detection is still limited by long-term instability, ion migration, and the presence of deep trap states that critically affect charge transport, and signal stability under ionizing radiation. Understanding defect dynamics is therefore essential to enable reliable detector operation.
Here, we investigate defect states and radiation hardness across different perovskite systems, combining studies on 3D and 2D lead halide crystals (MAPbBr₃ and PEA₂PbBr₄) with a mixed-cation, mixed-halide composition, relevant for scalable device architectures. Deep-level defects are probed using Photo-Induced Current Transient Spectroscopy (PICTS), a technique suited for high-resistivity materials and capable of resolving trap activation energies under operating-like conditions.
For the 2D layered perovskite (PEA)₂PbBr₄, PICTS measurements reveal clear fingerprint of deep trap states, with activation energies extracted through Arrhenius analysis. Thanks to the reduced ionic mobility of the 2D structure, these trap levels can be reliably identified and tracked under external stress. Importantly, the defect signature remains stable under thermal cycling, electrical bias, and prolonged X-ray irradiation, demonstrating strong intrinsic radiation tolerance. This behavior contrasts with 3D perovskites, where ion migration dominates the transient response and limits the extraction of defect parameters.
The technique has been further employed to investigate and to assess defect formation in thin film complex compositions. A single dominant trap level is identified, consistent with interstitial halide defects. Time-dependent and bias-dependent measurements indicate a relatively stable defect population, despite the increased compositional disorder. To enhance environmental robustness and ensure stable detector operation, a Cytop capping layer is introduced, effectively reducing interaction with moisture and oxygen and changing the defective levels.
A comparative analysis between single crystals and polycrystalline films highlights the impact of morphology on charge transport and defect sensitivity. Furthermore, X-ray exposure studies suggest a correlation between defect evolution and improved operational stability, potentially linked to radiation-induced defect passivation. Overall, these results provide key insights into defect-controlled charge transport in MHP-based detectors and demonstrate that 2D perovskites and optimized mixed-cation systems offer a viable pathway toward radiation-hard, stable, and scalable direct X-ray detection technologies.