Shape‐Dependent Kinetics of Halide Vacancy Filling in Organolead Halide Perovskites

Abstract

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...

Electroluminescence of Halide Perovskite Single Crystals Showing Stochastically Active Multiple Emitting Centers

“…The long ON-time cutoff is attributed to bromide vacancy filling and decreases in the rates of trapping–de-trapping and charging–discharging. This result is consistent with PL blinking suppression or PL intensity enhancement by halide vacancy filling in MAPbX 3 . ,, For example, Jin et al demonstrated PL blinking suppression in MAPbI 3 NCs doped with Cl . Also, they observed a longer PL lifetime for the Cl-dopped NCs.…”

Highly Luminescent and Stable Halide Perovskite Nanocrystals by Interfacial Defect Passivation and Amphiphilic Ligand Capping

“…These results substantiate the passivation of halide vacancy in poorly luminescing PNCs by NaBr treatment, leading to an ensemble-averaged increase in Φ of the sample. Recently, we have reported halide vacancy passivation and PL blinking suppression in MAPbX 3 (X = Br, I) single nano- and microcrystals by supplying the samples with excess MAX in an organic solvent. , Nevertheless, our current work emphasizes the stability and improved PL properties of PNCs in water and other polar solvents.…”

Thermodynamically and Kinetically Controlled Nucleation and Growth of Halide Perovskite Single Crystals

“…In the RTC method, the method described in the previous report was modified. [ 31 ] A 1:1 mixture of GBL and 1 m MAPbBr 3 precursor solution was prepared, and 2 µL of this mixture was placed on an ITO‐coated slide glass and left at room temperature for 30 min. After the crystallization of MAPbBr 3 MCs, the surplus solvent was absorbed using filter paper.…”

“…Conversely, several groups reported perovskite crystallization using N ‐cyclohexyl‐2‐pyrrolidone (CHP) as an additive to control the HP crystal shape. [ 28–32 ] Lee et al. prepared a homogeneous perovskite film using CHP as a morphology‐controlling agent.…”

“…Conversely, several groups reported perovskite crystallization using N-cyclohexyl-2-pyrrolidone (CHP) as an additive to control the HP crystal shape. [28][29][30][31][32] Lee et al prepared a homogeneous perovskite film using CHP as a morphology-controlling agent. [28] Garcia-Aboal et al demonstrated uniform shape and size MAPbBr 3 crystal synthesis by spin-coating with adding CHP.…”