Ihor Cherniukh

Bio: Ihor Cherniukh is an academic researcher from ETH Zurich. The author has contributed to research in topics: Perovskite (structure) & Materials science. The author has an hindex of 6, co-authored 9 publications receiving 700 citations. Previous affiliations of Ihor Cherniukh include Swiss Federal Laboratories for Materials Science and Technology.

Detection of gamma photons using solution-grown single crystals of hybrid lead halide perovskites

Abstract: Cheap and sensitive gamma-ray detectors are desired for defence, medical and research applications. Solid-state gamma-radiation detectors made from solution-grown perovskites have now been demonstrated for multiple practical applications.

Manganese(II) in Tetrahedral Halide Environment: Factors Governing Bright Green Luminescence

Abstract: Finding narrow-band light emitters for the visible spectral region remains an immense challenge. Such phosphors are in great demand for solid-state lighting and display application. In this context...

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

Abstract: 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 Zurich 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.

Perovskite-type superlattices from lead halide perovskite nanocubes

Abstract: Atomically defined assemblies of dye molecules (such as H and J aggregates) have been of interest for more than 80 years because of the emergence of collective phenomena in their optical spectra1–3, their coherent long-range energy transport, their conceptual similarity to natural light-harvesting complexes4,5, and their potential use as light sources and in photovoltaics. Another way of creating versatile and controlled aggregates that exhibit collective phenomena involves the organization of colloidal semiconductor nanocrystals into long-range-ordered superlattices6. Caesium lead halide perovskite nanocrystals7–9 are promising building blocks for such superlattices, owing to the high oscillator strength of bright triplet excitons10, slow dephasing (coherence times of up to 80 picoseconds) and minimal inhomogeneous broadening of emission lines11,12. So far, only single-component superlattices with simple cubic packing have been devised from these nanocrystals13. Here we present perovskite-type (ABO3) binary and ternary nanocrystal superlattices, created via the shape-directed co-assembly of steric-stabilized, highly luminescent cubic CsPbBr3 nanocrystals (which occupy the B and/or O lattice sites), spherical Fe3O4 or NaGdF4 nanocrystals (A sites) and truncated-cuboid PbS nanocrystals (B sites). These ABO3 superlattices, as well as the binary NaCl and AlB2 superlattice structures that we demonstrate, exhibit a high degree of orientational ordering of the CsPbBr3 nanocubes. They also exhibit superfluorescence—a collective emission that results in a burst of photons with ultrafast radiative decay (22 picoseconds) that could be tailored for use in ultrabright (quantum) light sources. Our work paves the way for further exploration of complex, ordered and functionally useful perovskite mesostructures. Through precise structural engineering, perovskite nanocrystals are co-assembled with other nanocrystal materials to form a range of binary and ternary perovskite-type superlattices that exhibit superfluorescence.

Halide Perovskite Photovoltaics: Background, Status, and Future Prospects

Abstract: The photovoltaics of organic–inorganic lead halide perovskite materials have shown rapid improvements in solar cell performance, surpassing the top efficiency of semiconductor compounds such as CdTe and CIGS (copper indium gallium selenide) used in solar cells in just about a decade. Perovskite preparation via simple and inexpensive solution processes demonstrates the immense potential of this thin-film solar cell technology to become a low-cost alternative to the presently commercially available photovoltaic technologies. Significant developments in almost all aspects of perovskite solar cells and discoveries of some fascinating properties of such hybrid perovskites have been made recently. This Review describes the fundamentals, recent research progress, present status, and our views on future prospects of perovskite-based photovoltaics, with discussions focused on strategies to improve both intrinsic and extrinsic (environmental) stabilities of high-efficiency devices. Strategies and challenges regardi...

Methylammonium Chloride Induces Intermediate Phase Stabilization for Efficient Perovskite Solar Cells

Abstract: Summary One of the most effective methods to achieve high-performance perovskite solar cells has been to include additives that serve as dopants, crystallization agents, or passivate defect sites. Cl-based additives are among the most prevalent in literature, yet their exact role is still uncertain. In this work, we systematically study the function of methylammonium chloride (MACl) additive in formamidinium lead iodide (FAPbI3)-based perovskite. Using density functional theory, we provide a theoretical framework for understanding the interaction of MACl with a perovskite. We show that MACl successfully induces an intermediate to the pure FAPbI3 α-phase without annealing. The formation energy is related to the amount of incorporated MACl. By tuning the incorporation of MACl, the perovskite film quality can be significantly improved, exhibiting a 6× increase in grain size, a 3× increase in phase crystallinity, and a 4.3× increase in photoluminescence lifetime. The optimized solar cells achieved a certified efficiency of 23.48%.

High efficiency planar-type perovskite solar cells with negligible hysteresis using EDTA-complexed SnO2

Abstract: Even though the mesoporous-type perovskite solar cell (PSC) is known for high efficiency, its planar-type counterpart exhibits lower efficiency and hysteretic response. Herein, we report success in suppressing hysteresis and record efficiency for planar-type devices using EDTA-complexed tin oxide (SnO2) electron-transport layer. The Fermi level of EDTA-complexed SnO2 is better matched with the conduction band of perovskite, leading to high open-circuit voltage. Its electron mobility is about three times larger than that of the SnO2. The record power conversion efficiency of planar-type PSCs with EDTA-complexed SnO2 increases to 21.60% (certified at 21.52% by Newport) with negligible hysteresis. Meanwhile, the low-temperature processed EDTA-complexed SnO2 enables 18.28% efficiency for a flexible device. Moreover, the unsealed PSCs with EDTA-complexed SnO2 degrade only by 8% exposed in an ambient atmosphere after 2880 h, and only by 14% after 120 h under irradiation at 100 mW cm−2. The development of high efficiency planar-type perovskite solar cell has been lagging behind the mesoporous-type counterpart. Here Yang et al. modify the oxide based electron transporting layer with organic acid and obtain planar-type cells with high certified efficiency of 21.5% and decent stability.

Lead Halide Perovskite Nanocrystals in the Research Spotlight: Stability and Defect Tolerance

Abstract: This Perspective outlines basic structural and optical properties of lead halide perovskite colloidal nanocrystals, highlighting differences and similarities between them and conventional II–VI and III–V semiconductor quantum dots. A detailed insight into two important issues inherent to lead halide perovskite nanocrystals then follows, namely, the advantages of defect tolerance and the necessity to improve their stability in environmental conditions. The defect tolerance of lead halide perovskites offers an impetus to search for similar attributes in other related heavy metal-free compounds. We discuss the origins of the significantly blue-shifted emission from CsPbBr3 nanocrystals and the synthetic strategies toward fabrication of stable perovskite nanocrystal materials with emission in the red and infrared parts of the optical spectrum, which are related to fabrication of mixed cation compounds guided by Goldschmidt tolerance factor considerations. We conclude with the view on perspectives of use of th...

Cs 2 AgBiBr 6 single-crystal X-ray detectors with a low detection limit

Abstract: Sensitive X-ray detection is crucial for medical diagnosis, industrial inspection and scientific research. The recently described hybrid lead halide perovskites have demonstrated low-cost fabrication and outstanding performance for direct X-ray detection, but they all contain toxic Pb in a soluble form. Here, we report sensitive X-ray detectors using solution-processed double perovskite Cs2AgBiBr6 single crystals. Through thermal annealing and surface treatment, we largely eliminate Ag+/Bi3+ disordering and improve the crystal resistivity, resulting in a detector with a minimum detectable dose rate as low as 59.7 nGyair s−1, comparable to the latest record of 0.036 μGyair s−1 using CH3NH3PbBr3 single crystals. Suppressed ion migration in Cs2AgBiBr6 permits relatively large external bias, guaranteeing efficient charge collection without a substantial increase in noise current and thus enabling the low detection limit. Double perovskite Cs2AgBiBr6 single crystals are used to make a sensitive X-ray detector. The device exhibits a high sensitivity of 105 µC Gyair −1 cm−2 and a low detection limit of 59.7 nGyairs−1, and demonstrates long-term operational stability.