Thickness-Controlled Large Area (over 2500 cm²) Perovskite Single Crystal for X-Ray Imaging Applications

In recent years, metal halide perovskite (MHP) has been actively studied in the fields of solar cells, light emitting diodes and X-ray detectors due to its excellent optical properties. In particular, large diffusion length, high resistivity, high attenuation coefficients and tunable band gap make MHP as an attractive candidate as a photon-absorber for direct x-ray detector application. Furthermore, MHP in the form of single crystal is attracting a lot of attention due to its lower defect density and higher mobility-lifetime product values than MHP thin films.<br/>However, there still exist several issues to be addressed for MHP single crystal to be incorporated into commercial X-ray detectors. The primary issue is the synthesis of large-area single crystals while keeping its thickness on the order of mm—a thicker absorber will reduce charge collection efficiency and a thinner absorber causes insufficient X-ray absorption. In a conventional solution method of growing MHP single crystal, where a single crystal grows in free-standing configuration, the growth along the lateral dimensions is accompanied by the increase of the thickness. In order to utilize a free-standing single crystal for x-ray imaging, the crystal must be sliced or grinded into a smaller thickness, during which there is a high risk of crack formation or fracture due to highly brittle nature of MHP single crystal. In addition, a considerable amount of the material is wasted.<br/>In this study, we designed a novel growth apparatus that allows us to grow MHP single crystals as large as 50 mm X 50 mm while limiting the thickness to 1 mm with no need for post-processing to reduce the thickness to apply for X-ray detectors. We fabricated X-ray detectors with our large-scale and thin single crystal and they exhibited an excellent sensitivity of 3.0x104 μC Gyair−1 cm−2. Thin film transistor panel integrated X-ray detector was also fabricated for large-scale imaging. The details of the synthesis of MHP single crystals as well as device characterizations will be discussed.