Perovskite Materials for Radiation Detection

Semiconductor materials currently used in radiation detectors are very expensive and require processing at high temperatures. Perovskites, CH₃NH₃PbX₃ (X=Br, I), were chosen to be evaluated for this application due to their unique semiconductor properties such as long diffusion lengths and ambipolar charge transport at a low cost and energy to produce. According to theoretical values, a perovskite between 3 µm and 6 µm is needed to capture a 1.4 MeV alpha particle produced when a neutron from a californium-252 source impacts a boron atom in a conventional conversion layer. In order to reach these thicknesses, initial research was completed on solution processed perovskite active layers (~ 400 nm) for solar cells. It became apparent that the iodide-based solvent processed materials degraded too quickly to be used in a detector. To grow thicker layers without potential solvent-assisted degradation, a two-step solvent free deposition of perovskites was developed using a close space sublimation system. These films easily reach 3 µm and are more stable, but they still possess inherent traits of a thin film. Therefore, perovskite single crystals were grown to have a structurally perfect material with no voids. These crystals are able to be doped with neutron sensitive materials such as boron or gadolinium, and can be grown large enough to capture a thermal neutron and convert it to an alpha particle inside of the crystal, without the use of a conversion layer. The deposition of these perovskite materials has thus been developed and optimized for their use in future radiation detectors.