CsSnI3 is a potential lead-free inorganic perovskite for solar energy applications due to its nontoxicity and attractive optoelectronic properties. Despite these advantages, photovoltaic cells using ...CsSnI3 have not been successful to date, in part due to low stability. We demonstrate how gradual substitution of Rb for Cs influences the structural, thermodynamic, and electronic properties on the basis of first-principles density functional theory calculations. By examining the effect of the Rb:Cs ratio, we reveal a correlation between octahedral distortion and band gap, including spin–orbit coupling. We further highlight the cation-induced variation of the ionization potential (work function) and the importance of surface termination for tin-based halide perovskites for engineering high-performance solar cells.
In principle, the induced chirality of hybrid perovskites results from symmetry-breaking within inorganic frameworks. However, the detailed mechanism behind the chirality transfer remains unknown due ...to the lack of systematic studies. Here, using the structural isomer with different functional group location, we deduce the effect of hydrogen-bonding interaction between two building blocks on the degree of chirality transfer in inorganic frameworks. The effect of asymmetric hydrogen-bonding interaction on chirality transfer was clearly demonstrated by thorough experimental analysis. Systematic studies of crystallography parameters confirm that the different asymmetric hydrogen-bonding interactions derived from different functional group location play a key role in chirality transfer phenomena and the resulting spin-related properties of chiral perovskites. The methodology to control the asymmetry of hydrogen-bonding interaction through the small structural difference of structure isomer cation can provide rational design paradigm for unprecedented spin-related properties of chiral perovskite.
Halide perovskites are excellent candidate materials for use in solar cell, LED, and detector devices, in part because their composition can be tuned to achieve ideal optoelectronic properties. ...Empirical efficiency optimization has led the field toward compositions rich in FA (formamidinium) on the A‐site and I on the X‐site, with additional small amounts of MA (methylammonium) or Cs A‐site cations and Br X‐site anions. However, it is not clear how and why the specific compositions of alloyed, that is, mixed component, halide perovskites relate to photo‐stability of the materials. Here, this work combines synchrotron grazing incidence wide‐angle X‐ray scattering, photoluminescence, high‐resolution scanning electron diffraction measurements and theoretical modelling to reveal the links between material structure and photostability. Namely, this work finds that increased octahedral titling leads to improved photo‐stability that is correlated with lower densities of performance‐harming hexagonal polytype impurities. These results uncover the structural signatures underpinning photo‐stability and can therefore be used to make targeted changes to halide perovskites, bettering the commercial prospects of technologies based on these materials.
The long‐term instability of halide perovskite semiconductors hinders their commercial adoption. In this paper, it is found that the magnitude of octahedral tilting in the crystal structures of alloyed formamidinium‐rich halide perovskites can be controlled by their composition, and that greater tilting leads to more photo‐stable films with fewer performance‐limiting hexagonal phase impurities.
The metal halide Cs3Cu2I5 displays anomalous optical properties: an optical absorption onset in the ultraviolet region (∼ 330 nm) with highly efficient luminescence in the blue region (∼ 445 nm). ...Although self-trapped exciton formation has been proposed as the origin of giant Stokes shift, its connection to the photoluminescence quantum yield exceeding 90% remains unknown. Here, we explore the photochemistry of Cs3Cu2I5 from first-principles and reveal a low energy barrier for exciton self-trapping associated with Cu–Cu dimerization. Kinetic analysis shows that the quantum yield of blue emission in Cs3Cu2I5 is sensitive to the excited carrier density due to the competition between exciton self-trapping and band-to-band radiative recombination.
Control of the stability, transport, and confinement of charge carriers (electrons and holes) at interfaces is a key requirement to realize robust halide perovskite devices. The PbS–CsPbBr3 interface ...is atomically matched with low lattice strain, opening the potential for epitaxial growth. We assess the atomic nature of the interface using first-principles density functional theory calculations to identify (1) the thermodynamically stable (100) surface termination of the halide perovskite; (2) the most favorable (100)|(100) contact geometry; (3) the strong interfacial chemical bonding between PbS and CsPbBr3; (4) the type I (straddling) band alignment that enables electron and hole confinement in the lead sulfide layer. The combination of metal halide perovskites and IV–VI semiconductors represents an important platform for probing interfacial chemical processes and realizing new functionality.
Abstract
Over the past decade, metal halide perovskites (MHPs) have received great attention, triggered by the tremendous success of their record‐breaking power conversion efficiency values in solar ...cells. Recently, there have been significant interests in fully utilizing their unique properties by exploring other device applications including thermoelectrics, which is promising due to their ultralow thermal conductivity and high mobility relative to their competitors among solution‐processable materials. However, the performance of MHP thermoelectrics reported so far falls significantly short of theoretical predictions, as the doping levels achieved to date are typically below the optimum values for maximizing the thermoelectric power factor, indicating the need for effective electrical doping strategies. In this critical review, recent studies aimed at enhancing the thermoelectric properties of MHPs are discussed, with a focus on the relatively under‐explored area of electrical doping in MHPs. The underlying charge transport mechanism and doping effect on transport are also examined. Finally, the challenges facing MHP thermoelectrics are highlighted, and potential research visions for achieving highly efficient thermoelectric conversion based on MHPs are offered.
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The behavior of grain boundaries in polycrystalline halide perovskite solar cells remains poorly understood. Whereas theoretical studies indicate that grain boundaries are not active for ...electron–hole recombination, there have been observations of higher nonradiative recombination rates involving these extended defects. We find that iodine interstitial defects, which have been established as a recombination center in bulk crystals, tend to segregate at planar defects in CsPbI3. First-principles calculations show that enhanced structural relaxation of the defects at grain boundaries results in increased stability (higher concentration) and deeper trap states (faster recombination). We show how the grain boundary can be partly passivated by halide mixing or extrinsic doping, which replaces or suppresses the formation of trap states close to the grain boundaries.
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