Ultra-Stable and Robust Response to X-Rays in 2D Layered Perovskite Micro-Crystalline Films Directly Deposited on Flexible Substrate

The demand for large area, low cost and flexible high-energy radiation detection systems for medical imaging and public security, has pushed the research to develop novel detectors combining high sensitivity and low-cost fabrication processes. Recently, lead-halide perovskites emerged as a very promising novel class of materials for X- and gamma-ray detection. Their success can be attributed to the excellent perovskite optoelectronic properties. The presence of heavy elements like Pb, Br or I inside the lead-halide perovskite structure ensures a high effective atomic number, resulting in a high absorption coefficient in the ionizing radiation energy range. For efficient detection, high absorption is not enough. The transport properties of the material also play a crucial role. Carrer diffusion length of over 1μm and long carrier lifetime has been attributed to perovskite even in polycrystalline form. Moreover, these materials can be fabricated at low temperature from solution opening the possibility to low-cost, large-area and flexible detectors. Among the lead-halide perovskite, 2D layered hybrid perovskites have recently attracted increasing attention as active layers in LEDs and UV-Vis photodetector. 2D perovskites crystallize in a natural self-assembled quantum well-like structure and possess several interesting features. Even if the transport properties of 2D perovskite are inferior to the 3D perovskite, they are an interesting alternative because of the superior ambient stability. In this work, we fabricate a direct X-ray detector based on PEA2PbBr4 directly deposited on PET substrate with pre patterned interdigitated metal contacts. The perovskite deposited by single step spin-coating forms a polycrystalline film with an average grain size of 33.5 ± 8.3 μm and thickness of 1.9 ± 0.8 μm. The properties and performances of the devices were tested first under UV light and then under X-ray radiation with different energies, 40-150keV. Under pulsed laser, the material showed a fast response with a rise time of 147 ± 10 ns. The excellent X-ray detection performances are demonstrated by the two figures of merits sensitivity and limit of detection. The devices showed and high sensitivity under 150kVp X-ray radiation with a top value of 806 μC Gy−1 cm−2. The higher bandgap of the material with respect to 3D perovskite leads to dark current values <1pA at 20V. The extremely low and stable dark current allowed to detect very low incident dose rates. We demonstrated a very low limit of detection with values down to 42 nGy s−1. Additionally, the tested devices exhibit exceptionally stable response under constant irradiation and bias, assessing the material robustness. The performances of the X-ray detectors fabricated on flexible substrates have been tested under different bending conditions to assess the effect of the mechanical stress on the perovskite layer.