halide vacancies/ions is an important factor in the excitonic and charge carrier properties of perovskites. [4g,h] For example, the hole trap-mediated nonradiative charge recombination in CH 3 NH 3 PbI 3 is correlated with the oxidation state of the iodine vacancy. [4h] While an I V − vacancy does not create a hole trap state, a neutral I V vacancy forms a hole trap near the conduction band and accelerates nonradiative charge recombination. Similarly, an I V + vacancy accelerates nonradiative charge recombination by forming shallow and deep hole traps. Like I vacancies, Cl or Br vacancies with different oxidation states form shallow and deep traps and influence the nonradiative exciton/charge carrier recombination rate. A chemical additive or photoactivation fills these anion vacancies. In the former case, halide ions from halogen gases, [8] halogen compounds AX [9] (A = MA/FA/Cs/Na/K and X = Cl/Br/I), organic pseudohalides, [10] or ligands [11] fill the vacancies. In the latter case, the so-called light soaking effect, molecules like oxygen improve the PL of LHPs by photoinduced defect passivation. [6c,d,12] For example, a superoxide generated by self-sensitization occupies the halide vacancy and improves the optical properties of LHPs. [6c,f ] Also, an oxide layer (e.g., PbO) on the LHP surface increases the sample stability against humidity and decreases the trap-assisted nonradiative recombination rate. [6e] Defect passivation during photoexcitation involves lattice expansion and compositional redistribution through ion migration. [12a,b,h] Crystal shapes and optical properties are equally important for the electro-optical applications of LHPs. [3a,13] Information about the LHP crystal shape-dependent halide vacancy filling by a halide precursor or the light can help optimize the properties and applications of LHPs. Nevertheless, a correlation among the structure, shape, size, defects, and degradation rate of perovskites remains concealed.We report the surface-to-volume (s-t-v) ratio-dependent PL stability, halide vacancy filling, and carrier recombination rates in methylammonium lead bromide (MAPbBr 3 ) single crystals with the cubic, plate, or rod shape. The Br − vacancies are filled by soaking the crystals in a MABr solution or a picosecond laser beam. We discuss the s-t-v ratio-dependent kinetics of Br − vacancy filling from the viewpoint of redistribution in the radiative and nonradiative recombination rates. Results and DiscussionTo understand the shape-dependent halide vacancy filling, we synthesized MAPbBr 3 microrods, microplates, and microcubes.Halide perovskites show high photoluminescence quantum yields and tunable bandgap. While perovskites' optical properties significantly degrade due to the ionic and electronic defects, a correlation among their structure, size, defects, and degradation rate remains concealed. The authors report the crystal shape-and halide vacancy-dependent stability of methylammonium lead bromide single crystals. The vacancies are filled in the cubic-, plate-, and r...

Halide perovskites are materials for future optical displays and solar cells. Electron donor-acceptor perovskite heterostructures with distinguishing halide compositions are promising for transporting and harvesting photogenerated charge carriers. Combined ebeam lithography and anion exchange are promising to develop such heterostructures but challenging to prepare multiple heterojunctions at desired locations in single crystals. We demonstrate swift laser trappingassisted band gap engineering at the desired locations in MAPbBr 3 microrods, microplates, or nanocrystal thin films. The built-in donor-acceptor double and multiheterojunction structures let us transport and trap photogenerated charge carriers from wide-band gap bromide to narrow-band gap iodide domains. We discuss the charge carrier transport and trapping mechanisms from the viewpoints of engineered bands and band continuity. This work offers a convenient method for designing single-, double-and multi-heterojunction donor-acceptor halide perovskites for photovoltaic, photonic, and electronic applications.

Halide perovskites have become the core materials for next‐generation photovoltaic and optoelectronic devices. However, halide vacancies in perovskite crystals adversely affect their optical and electronic properties and stability. The research by Takuya Okamoto, Md. Shahjahan, and Vasudevanpillai Biju (article number 2100355) demonstrates halide vacancy filling by light‐soaking of perovskite crystals soaked in a halide ion solution. The rate of vacancy filling is crystal‐shape and size‐dependent, showing the relationship among the surface‐to‐volume ratio, defect density, and defect passivation rate.

The emission color and bandgap …ofhalide perovskites are routinely tuned by halide mixing or quantum confinement. In their Communication (e202215947), Va sudevanpillai Biju and co-workers demonstrate selective exciton and carrier recombination in donor-acceptor bandgap engineered halide perovskite single crystals or nanocrystal films to show color tuning at desired locations.B yr eal-time stitching of an arrow bandgap iodide domain in aw ide bandgap microrod, microplate or nanocrystal sample,e xcitons and carriers are quantitatively transferred from the green-emitting bromide regions to the red-emitting iodide domain.

Halide perovskites are materials for future optical displays and solar cells. Electron donor‐acceptor perovskite heterostructures with distinguishing halide compositions are promising for transporting and harvesting photogenerated charge carriers. Combined e‐beam lithography and anion exchange are promising to develop such heterostructures but challenging to prepare multiple heterojunctions at desired locations in single crystals. We demonstrate swift laser trapping‐assisted band gap engineering at the desired locations in MAPbBr3 microrods, microplates, or nanocrystal thin films. The built‐in donor‐acceptor double and multi‐heterojunction structures let us transport and trap photogenerated charge carriers from wide‐band gap bromide to narrow‐band gap iodide domains. We discuss the charge carrier transport and trapping mechanisms from the viewpoints of engineered bands and band continuity. This work offers a convenient method for designing single‐, double‐ and multi‐heterojunction donor‐acceptor halide perovskites for photovoltaic, photonic, and electronic applications.