Although known since the late 19th century, organic–inorganic perovskites have recently received extraordinary research community attention because of their unique physical properties, which make them promising candidates for application in photovoltaic (PV) and related optoelectronic devices. This review will explore beyond the current focus on three-dimensional (3-D) lead(II) halide perovskites, to highlight the great chemical flexibility and outstanding potential of the broader class of 3-D and lower dimensional organic-based perovskite family for electronic, optical, and energy-based applications as well as fundamental research. The concept of a multifunctional organic–inorganic hybrid, in which the organic and inorganic structural components provide intentional, unique, and hopefully synergistic features to the compound, represents an important contemporary target.

Organic–Inorganic Perovskites: Structural Versatility for Functional Materials Design

VASPKIT: A user-friendly interface facilitating high-throughput computing and analysis using VASP code

Lighting accounts for one-fifth of global electricity consumption1. Single materials with efficient and stable white-light emission are ideal for lighting applications, but photon emission covering the entire visible spectrum is difficult to achieve using a single material. Metal halide perovskites have outstanding emission properties2,3; however, the best-performing materials of this type contain lead and have unsatisfactory stability. Here we report a lead-free double perovskite that exhibits efficient and stable white-light emission via self-trapped excitons that originate from the Jahn–Teller distortion of the AgCl6 octahedron in the excited state. By alloying sodium cations into Cs2AgInCl6, we break the dark transition (the inversion-symmetry-induced parity-forbidden transition) by manipulating the parity of the wavefunction of the self-trapped exciton and reduce the electronic dimensionality of the semiconductor4. This leads to an increase in photoluminescence efficiency by three orders of magnitude compared to pure Cs2AgInCl6. The optimally alloyed Cs2(Ag0.60Na0.40)InCl6 with 0.04 per cent bismuth doping emits warm-white light with 86 ± 5 per cent quantum efficiency and works for over 1,000 hours. We anticipate that these results will stimulate research on single-emitter-based white-light-emitting phosphors and diodes for next-generation lighting and display technologies. After alloying with metal cations, a lead-free halide double perovskite shows stable performance and remarkably efficient white-light emission, with possible applications in lighting and display technologies.

Efficient and stable emission of warm-white light from lead-free halide double perovskites

Methylammonium Chloride Induces Intermediate Phase Stabilization for Efficient Perovskite Solar Cells

All highly-efficient organic–inorganic halide perovskite (OIHP) solar cells to date are made of polycrystalline perovskite films which contain a high density of defects, including point and extended imperfections. The imperfections in OIHP materials play an important role in the process of charge recombination and ion migration in perovskite solar cells (PSC), which heavily influences the resulting device energy conversion efficiency and stability. Here we review the recent advances in passivation of imperfections and suppressing ion migration to achieve improved efficiency and highly stable perovskite solar cells. Due to the ionic nature of OIHP materials, the defects in the photoactive films are inevitably electrically charged. The deep level traps induced by particular charged defects in OIHP films are major non-radiative recombination centers; passivation by coordinate bonding, ionic bonding, or chemical conversion have proven effective in mitigating the negative impacts of these deep traps. Shallow level charge traps themselves may contribute little to non-radiative recombination, but the migration of charged shallow level traps in OIHP films results in unfavorable band bending, interfacial reactions, and phase segregation, influencing the carrier extraction efficiency. Finally, the impact of defects and ion migration on the stability of perovskite solar cells is described.

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Imperfections and their passivation in halide perovskite solar cells

Substituting the toxic lead (Pb) in Pb halide perovskites by less harmful Sn is an attractive approach towards obtaining environment-friendly perovskite solar cells. However, complete substitution of Pb by Sn undermines the stability of perovskite materials and devices. Therefore, partial substitution of Pb by Sn has attracted much interest to balance environmental considerations and device performance. Here, we exploit the Sn ratio to optimize the band alignment in Pb–Sn mixed perovskite solar cells with an inverted structure. The band edge properties of Pb–Sn mixed triple cation perovskites (Cs/MA/FAPb1−xSnxX3, X = Cl, Br, I) for efficient inverted solar cells are studied via simulation and experiment. The optimized solar cell with x = 0.336 shows the highest power conversion efficiency of 16.10% along with negligible hysteresis. We demonstrate that the devices are stable and maintain 93% of the initial PCE under ambient conditions for 30 days. These results suggest that bandgap engineering is a feasible approach to balance the efficiency and stability of Pb–Sn mixed PSCs.

Band alignment of Pb–Sn mixed triple cation perovskites for inverted solar cells with negligible hysteresis

Electrides are unique in the sense that they contain localized anionic electrons in the interstitial regions. Yet they exist with a diversity of chemical compositions, especially under extreme conditions, implying generalized underlying principles for their existence. What is rarely observed is the combination of electride state and superconductivity within the same material, but such behavior would open up a new category of superconductors. Here, we report a hexagonal Nb5Ir3 phase of Mn5Si3-type structure that falls into this category and extends the electride concept into intermetallics. The confined electrons in the one-dimensional cavities are reflected by the characteristic channel bands in the electronic structure. Filling these free spaces with foreign oxygen atoms serves to engineer the band topology and increase the superconducting transition temperature to 10.5 K in Nb5Ir3O. Specific heat analysis indicates the appearance of low-lying phonons and two-gap s-wave superconductivity. Strong electron–phonon coupling is revealed to be the pairing glue with an anomalously large ratio between the superconducting gap Δ
 0 and T
 c, 2Δ
 0/k
 B
 T
 c = 6.12. The general rule governing the formation of electrides concerns the structural stability against the cation filling/extraction in the channel site. Coexistence of electride behavior and superconductivity is observed in a hexagonal phase of a Nb5Ir3 intermetallic with tunable electronic properties by introducing foreign atoms. A team led by Yaoqing Zhang and Hideo Hosono from Japan Science and Technology Agency and Tokyo Institute of Technology report a new hexagonal phase in the phase diagram of Nb–Ir binary intermetallics with interesting interplay of superconductivity and electride state. The electride state is formed by electrons detaching from the atoms but localizing in a one-dimensional channel space. This electride becomes a superconductor below a transition temperature of about 9.4 K, which could be enhanced to 10.5 K upon filling interstitial cavities with foreign oxygens. The results suggest a general rule governing the formation of electrides and form the basis for novel stable functional electrides.

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Electride and superconductivity behaviors in Mn 5 Si 3 -type intermetallics

We report bulk superconductivity of ternary equiatomic pnictides LaMP ($M$ = Ir and Rh; P = P and As) along with the crystal structure and physical properties (resistivity, magnetization, and heat capacity). It crystallized in a noncentrosymmetric structure type (space group $I$4${}_{1}$md, $Z$ = 4), which is an ordered ternary derivative of the centrosymmetric \ensuremath{\alpha}-ThSi${}_{2}$ structure. Three ternary pnictides showed superconductivity at low temperatures, and the highest critical temperature, ${T}_{c}$ = 5.3 K, was observed for LaIrP. The experimental and density functional calculations results suggested that LaMP could be categorized as a Bardeen--Cooper--Schrieffer superconductor with intermediate coupling. Considering the similar Sommerfeld value and Debye temperature, the differences in ${T}_{c}$ were attributed to the difference in the electron-phonon coupling strength in the compounds.

Superconductivity in noncentrosymmetric ternary equiatomic pnictides La MP ( M = Ir and Rh; P = P and As)

SnS is intrinsically a p-type semiconductor, and much effort has been made to attain n-type conduction. In this letter, we performed density functional theory calculations to seek an effective doping route for n-type SnS. It was found that aliovalent doping of SnS by Sb or Bi is not effective due to their high formation enthalpies; while the isovalent Pb-substitution of the Sn sites largely reduces formation enthalpies of Sn and Pb interstitials, which explain the recently demonstrated n-type conduction in the Sn1−xPbxS films fabricated under low H2S pressures.

Route to n-type doping in SnS

Suzuki cross-coupling reactions catalyzed by palladium are powerful tools for the synthesis of functional organic compounds. Excellent catalytic activity and stability require negatively charged Pd species and the avoidance of metal leaching or clustering in a heterogeneous system. Here we report a Pd-based electride material, Y3Pd2, in which active Pd atoms are incorporated in a lattice together with Y. As evidenced from detailed characterization and density functional theory (DFT) calculations, Y3Pd2 realizes negatively charged Pd species, a low work function and a high carrier density, which are expected to be beneficial for the efficient Suzuki coupling reaction of activated aryl halides with various coupling partners under mild conditions. The catalytic activity of Y3Pd2 is ten times higher than that of pure Pd and the activation energy is lower by nearly 35%. The Y3Pd2 intermetallic electride catalyst also exhibited extremely good catalytic stability during long-term coupling reactions.

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Zewen Xiao

Papers

Band alignment of Pb–Sn mixed triple cation perovskites for inverted solar cells with negligible hysteresis

Electride and superconductivity behaviors in Mn 5 Si 3 -type intermetallics

Superconductivity in noncentrosymmetric ternary equiatomic pnictides La MP ( M = Ir and Rh; P = P and As)

Route to n-type doping in SnS

Palladium-bearing intermetallic electride as an efficient and stable catalyst for Suzuki cross-coupling reactions