CsPbI3 inorganic perovskite has exhibited some special properties particularly crystal structure distortion and quantum confinement effect, yet the poor phase stability of CsPbI3 severely hinders its applications. Herein, the nature of the photoactive CsPbI3 phase transition from the perspective of PbI6 octahedra is revealed. A facile method is also developed to stabilize the photoactive phase and to reduce the defect density of CsPbI3. CsPbI3 is decorated with multifunctional 4‐aminobenzoic acid (ABA), and steric neostigmine bromide (NGBr) is subsequently used to further mediate the thin films' surface (NGBr‐CsPbI3(ABA)). The ABA or NG cation adsorbed onto the grain boundaries/surface of CsPbI3 anchors the PbI6 octahedra via increasing the energy barriers of octahedral rotation, which maintains the continuous array of corner‐sharing PbI6 octahedra and kinetically stabilizes the photoactive phase CsPbI3. Moreover, the added ABA and NGBr not only interact with shallow‐ or deep‐level defects in CsPbI3 to significantly reduce defect density, but also lead to improved energy‐level alignment at the interfaces between the CsPbI3 and the charge transport layers. Finally, the champion NGBr‐CsPbI3(ABA)‐based inorganic perovskite solar cell delivers 18.27% efficiency with excellent stability. Overall, this work demonstrates a promising concept to achieve highly phase‐stabilized inorganic perovskite with suppressed defect density for promoting its optoelectronic applications.

It is a great challenge to directly grow super long all‐inorganic perovskite monocrystalline wires due to the weak surface energy difference among the low index facets. Here, a one‐pot solution process to grow the aspect ratio over 105 of monocrystalline CsPbBr3 perovskite wires (PWs) and yield up to 70% is reported. A chemical potential dependent surface energy difference amplification strategy is proposed to regulate the surface energy of growing and grown surfaces accordingly to the anisotropic growth of CsPbBr3. The anisotropic growth of wires is derived from the regulation of anti‐solvent diffusion kinetic and the mass transfer kinetic control of the metal halide salts. This experiment demonstrates a 50 times amplification of surface energy difference. As‐produced PWs present a high photodetection responsivity up to 4923 A W−1, external quantum efficiency exceeding 13 784%, and detectivity over 3.6 × 1013 Jones. This work not only reveals the mechanism of surface energy dominated anisotropic growth for CsPbBr3 PWs, but also elucidates the important role of kinetics regulation during the growth process, which may open a new window for the low‐dimensional crystal growth of ionic compounds.

It is extremely challenging to grow single‐crystal halide perovskite films (SCHPFs) with not only desired transport properties but also large lateral size with much thinner thickness. Here, we report the growth of freestanding single crystal CsPbBr3 SCHPFs with thickness less than 100 nm and a lateral size close to centimeter for the first time. A new model for growth kinetics (Ψ=Aexp[−(EA−Es)/(kBT)]) is proposed to address the surface energy and temperature effect on the growth rate of ultrathin CsPbBr3 single‐crystal film. The experimental results and DFT calculations both demonstrated that the surfactant plays a critical role in modifying the surface energy and achieving anisotropic growth. This work opens new opportunities for high‐quality SCHPFs with large lateral size and controllable thickness that may find wide applications for optoelectronic devices.

In less than a decade, metal halide perovskites (MHPs) have been demonstrated as promising solar cell materials because the photoelectric conversion efficiency (PCE) of the representative material CH3NH3PbI3 rapidly increased from 3.8% in 2009 to 25.2% in 2009. However, defects play crucial roles in the rapid development of perovskite solar cells (PSCs) because they can influence the photovoltaic parameters of PSCs, such as the open circuit voltage, short-circuit current density, fill factor, and PCE. Among a series of superior optoelectronic properties, defect tolerance, i.e., the dominate defects are shallow and do not act as strong nonradiative recombination centers, is considered to be a unique property of MHPs, which is responsible for its surprisingly high PCE. Currently, the growth of PCE has gradually slowed, which is due to low concentrations of deep detrimental defects that can influence the performances of PSCs. To further improve the PCE and stability of PSCs, it is necessary to eliminate the impact of these minor detrimental defects in perovskites, including point defects, grain boundaries (GBs), surfaces, and interfaces, because nonradiative recombination centers seriously affect device performance, such as carrier generation and transport. Owing to its defect tolerance, most intrinsic point defects, such as VI and VMA, form shallow level traps in CH3NH3PbI3. The structural and electronic characteristics of the charged point defect VI − are similar to those of the unknown donor center in a tetrahedral semiconductor. It is a harmful defect caused by a large atomic displacement and can be passivated to strengthen chemical bonds and prevent atom migration by the addition of Br atoms. Owing to the ionic nature of MHPs and high ion migration speed, there are a large number of deep detrimental defects that can migrate to the interfaces under an electric field and influence the performance of PSCs. In addition, the ionic nature of MHPs results in surface/interface dangling bonds terminated with cations or anions; thus, deep defects can be passivated through Coulomb interactions between charged ions and passivators. Hence, the de-active deep-level traps resulting from charged defects can be passivated via coordinate bonding or ionic bonding. Usually, surface-terminated anions or cations can be passivated by corresponding cations or anions through ionic bonding, and Lewis acids or bases can be passivated through coordinated bonding. In this review, we not only briefly summarize recent research progress in defect tolerance, including the soft phonon mode and polaron effect, but also strategies for defect passivation, including ionic bonding with cations or anions and coordinated bonding with Lewis acids or bases.

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It is extremely challenging to grow single‐crystal halide perovskite films (SCHPFs) with not only desired transport properties but also large lateral size with much thinner thickness. Here, we report the growth of freestanding single crystal CsPbBr3 SCHPFs with thickness less than 100 nm and a lateral size close to centimeter for the first time. A new model for growth kinetics (Ψ=Aexp[−(EA−Es)/(kBT)]) is proposed to address the surface energy and temperature effect on the growth rate of ultrathin CsPbBr3 single‐crystal film. The experimental results and DFT calculations both demonstrated that the surfactant plays a critical role in modifying the surface energy and achieving anisotropic growth. This work opens new opportunities for high‐quality SCHPFs with large lateral size and controllable thickness that may find wide applications for optoelectronic devices.

The accurate band gap of 2.24 eV for hexagonal WO 3 is obtained by adopting the revised Heyd-Scuseria-Ernzerhof screened hybrid functional. The large band gap is a result of the off-centered symmetry where the W atom forms two short and two long bonds with four neighboring in-plane O atoms. By adding/removing electrons into/from the crystal, the effect of charge doping is investigated. With introducing electrons, the off-centered symmetry gets weakened with a slight narrowing in band gap. However, the doping lifts the Fermi level into the conduction band, inducing an increase in transition energy for electrons. Similarly, the hole doping also results in a remarkable increase in the transition energy. Such band structure modulation can be used in high efficient photoabsorption, photocatalysis and surface-enhanced Raman spectroscopy.

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