Single crystals of caesium formamidinium lead halide perovskites: solution growth and gamma dosimetry

Formamidinium (FA)-based hybrid lead halide perovskites (FAPbX3, X=I or Br/I) have recently led to significant improvements in the performance of perovskite photovoltaics. The remaining major pitfall is the instability of α-FAPbI3, causing the phase transition from the desired three-dimensional cubic perovskite phase to a non-perovskite one-dimensional hexagonal lattice. In this work, we report the facile, inexpensive, solution-phase growth of cm-scale single crystals (SCs) of variable composition CsxFA1−xPbI3−yBry (x=0–0.1, y=0–0.6) which exhibit improved phase stability compared to the parent α-FAPbI3 compound. These SCs possess outstanding electronic quality, manifested by a high-carrier mobility–lifetime product of up to 1.2 × 10−1 cm2 V−1 and a low dark carrier density that, combined with the high absorptivity of high-energy photons by Pb and I, allows the sensitive detection of gamma radiation. With stable operation up to 30 V, these novel SCs have been used in a prototype of a gamma-counting dosimeter. A synthesis that upends typical crystallization procedures makes it simpler to construct high-quality semiconductors for gamma-ray detectors. Monitoring for radioactive decay signatures requires materials with heavy atoms, such as lead, since they are strong absorbers of radiation. Maksym Kovalenko and colleagues from ETH Zürich now report that lead halide-based crystals with perovskite structures have advantages over existing radiation detectors. Instead of using typical complex fabrication procedures, the Swiss team grew semiconductors using liquid precursors that, unusually, crystallize faster at higher temperatures. Tweaking the perovskite's structure with formamidinium ions and caesium atoms produced centimetre-scale single crystals of mixed-cation perovskites that exhibited high mobility and low noise levels and were stable against phase transitions to non-perovskite structures for months. A prototype device based on open-source technology allowed sensitive detection of gamma radiation for minimal cost. Here we report an inexpensive, solution-phase growth of cm-scale single crystals of variable composition CsxFA1−xPbI3−yBry (FA=formamidinium, x=0–0.1, y=0–0.6), which exhibit improved phase stability compared to the parent α-FAPbI3 compound. High-carrier mobility–lifetime product of up to 1.2 × 10−1 cm2 V−1 and a low dark carrier density, combined with the high absorptivity of high-energy photons by Pb and I, allow the sensitive detection of gamma radiation. With stable operation up to 30 V, these novel perovskite materials have been used in a prototype of a gamma-counting dosimeter.