Summary Mixed-dimensional 2D/3D hybrid halide perovskites retain the stability of 2D perovskites (formula (A′)₂(A)_n−1Pb_nI3_n+1) and long diffusion lengths of the 3D materials (AMX₃), thereby affording devices with extended stability as well as state-of-the art efficiencies approaching those of the 3D materials. These films are made by spin-coating precursor solutions with an arbitrarily large average layer thickness n (⟨n⟩ > 7) to give films with both 2D and 3D phases. Although the 2D and 3D perovskite film formation mechanisms have been studied, little is understood about composite 2D/3D film formation. We used in-situ grazing-incidence wide-angle scattering with synchrotron radiation to characterize the films fabricated from precursor solutions with stoichiometries of (BA)₂(MA)_n−1Pb_nI_3n+1 (⟨n⟩ = 3, 4, 5, 7, 12, 50, and ∞ (MAPbI₃)). Four different mechanisms are seen depending on the stoichiometry in the precursor solution. Kinetic analysis shows faster and earlier growth of the solvate with increasing ⟨n⟩.

Spectroscopic-grade single crystal detectors can register the energies of individual X-ray interactions enabling photon-counting systems with superior resolution over traditional photoconductive X-ray detection systems. Current technical challenges have limited the preparation of perovskite semiconductors for energy-discrimination X-ray photon-counting detection. Here, this work reports the deployment of a spectroscopic-grade CsPbBr₃ Schottky detector under reverse bias for continuum hard X-ray detection in both the photocurrent and spectroscopic schemes. High surface barriers of ≈1 eV are formed by depositing solid bismuth and gold contacts. The spectroscopic response under a hard X-ray source is assessed in resolving the characteristic X-ray peak. The methodology in enhancing X-ray sensitivity by controlling the X-ray energies and flux, and voltage, is described. The X-ray sensitivity varies between a few tens to over 8000 μC Gyair⁻¹ cm⁻². The detectable dose rate of the CsPbBr₃ detectors is as low as 0.02 nGyair s⁻¹ in the energy discrimination configuration. Finally, the unbiased CsPbBr₃ device forms a spontaneous contact potential difference of about 0.7 V enabling high quality of the CsPbBr₃ single crystals to operate in “passive” self-powered X-ray detection mode and the X-ray sensitivity is estimated as 14 μC Gyair⁻¹ cm⁻². The great potential of spectroscopic-grade CsPbBr₃ devices for X-ray photon-counting systems is anticipated in this work.

The direct detection of high-energy radiation such as X-rays and γ-rays by semiconductors at room temperature is a challenging proposition that requires remarkably pure and nearly perfect crystals. The emergence of metal halide perovskites, defect-tolerant semiconductors, is reviving hope for new materials in this field after an almost 20 year hiatus. Metal halide perovskites, which combine exceptional optoelectronic properties, versatile chemistry and simple synthesis, are challenging traditional approaches for the development of novel semiconductors for detecting hard radiation. We discuss the relevant physical properties, promising materials, fabrication techniques and device architectures for high-performance, low-cost detectors by targeting next-generation semiconductors for radiation detection. We also present a perspective on the impact of such advances in future medical imaging applications.