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Lead halide perovskites are promising materials for the development of technologies such as radiation detectors, solar cells, and light-emitting diodes. Their advantages include a high absorption coefficient over a broad spectral range, attributed to the large atomic numbers of their constituent elements, a high mobility–lifetime product, long carrier diffusion lengths, low fabrication costs, and high defect tolerance. However, their practical application is limited by several drawbacks, including gradual degradation of contacts, instability under continuous illumination, and high dark current or environmental instability [1, 2, 3].
In this work, cesium lead bromide (CsPbBr$_3$, CPB), an all-inorganic perovskite grown by the Bridgman method, was studied. The 1.7 mm thick samples were prepared with evaporated square Au electrodes with dimensions of 10 mm x 10 mm. Furthermore, the cathode was a full electrode, while the anode consisted of an 8 mm x 8 mm central electrode (CE), a guard ring (GR) structure with a thickness of 0.5 mm, and a 0.5 mm gap between the CE and GR structure. Regions with inhomogeneities in the sample were observed in charge collection and photocurrent. Two measuring techniques were performed:
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TCT (Transient Current Technique) measurement of a 2D map of charge collection efficiency using a green laser
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photocurrent 2D mapping measurement using a green laser diode
In both cases, the individual responses of CE and GR were measured simultaneously.
The presence of inhomogeneities causes uneven charge collection in various regions of the sample. This further imposes broadening of the detected spectral lines, which decreases the resolution of the perovskite detectors. The origin of the inhomogeneities, or why they are concentrated almost exclusively at the edge of the sample, is still under research. It is proposed that during the growth of the CPB crystal in a quartz ampoule using the Bridgman method, a phase transition occurs in which the volume of the elementary cell increases. This imposes strain on the crystal, resulting in the formation of diagonal stripes (twins) in the crystal. When an external electric field is applied, the charge carriers preferentially drift along these stripes in a diagonal direction, thus accumulating at the edge of the sample.
[1] J. Wei et al., Halide lead perovskites for ionizing radiation detection, Nature Communications, 2019.
[2] S. Shrestha et al., X-ray Detectors Based on Halide Perovskite Materials, Coatings, 2023.
[3] K. Pekárková, R. Grill, M. Ledinský, et al., Light-Induced Surface Recombination Suppression, Carrier Lifetime Improvement, and Deep Defect Formation in Lead Halide Perovskites, Laser Photonics Rev19, no. 18, 2025.