Modulation of photodetection characteristics in MAPbBr3 perovskite NCs via Sn doping

We have synthesized a new class of organolead halide perovskite nanocrystals by a solvent-free mechanochemical green approach. We have developed a new combination of precursor by incorporating nitrate ions into the MAPbBr3 perovskite core. While the presence of nitrate ion is evidenced by Fourier-transform infrared spectra, X-ray diffraction data shows the formation of perovskite nanocrystals. By altering the precursor composition, the morphology of the nanocrystals changes. Photoluminescence properties of these nanocrystals are preserved. Moreover, the stability of these nanocrystals is monitored for a long time, which shows that the incorporation of nitrate ions into the perovskite nanocrystal core does not have any decremental effect on its stability. Nonetheless, this strategy to synthesize perovskite nanocrystals reduces the solvent toxicity.

Despite the excellent optoelectronic properties of halide perovskites, the ionic and electronic defects adversely affect the stability and durability of perovskites and their devices. These defects, intrinsic or produced by environmental factors such as oxygen, moisture, or light, not only cause chemical reactions that disintegrate the structure and properties of perovskites but also induce undesired photoluminescence blinking to perovskite quantum dots and nanocrystals. Blinking is also caused by the nonradiative Auger processes in the photocharged quantum dots or nanocrystals. Herein, we find real-time suppression of halide vacancy-assisted nonradiative exciton recombination and photoluminescence blinking in MAPbBr3 and MAPbI3 perovskite quantum dots by filling the vacancies using halide precursors (MABr and MAI). Also, halide vacancy filling increases the photoluminescence quantum efficiencies and lifetimes of the quantum dots. We estimate the rates of halide vacancy-assisted nonradiative recombination at 1 × 108 s-1 for MAPbBr3 and 1.9 × 109 s-1 for MAPbI3 quantum dots. The real-time blinking suppression using the halide precursors and statistical analysis of the ON/OFF blinking time reveal that the halide vacancies contribute to the type-A blinking through charging and discharging. Conversely, the blinking of the quantum dots after halide vacancy filling is dominated by the type-B mechanism.

The facile preparation, structural tunability, and unique optical properties of halide perovskites have led to great success in solar cells and light-emitting devices. However, due to their instability in low-cost polar solvents (e.g., methanol and water), their application in photocatalysis is currently lagging and usually requires special encapsulation. Herein, we demonstrate that halide perovskite (MAPbBr3, CsPbBr3) nanocrystals are stable for photocatalytic hydrogen production from methanol/water vapor as proton sources without special protection in the presence of Pt cocatalysts. In methanol vapor, an optimal MAPbBr3 perovskite NC film exhibits steady hydrogen evolution for ∼20 h under solar irradiation, reaching a marked hydrogen evolution rate of 424 μmol·g–1·h–1. Notably, time-resolved spectroscopies reveal that the diffusion-limited feeding of electron–hole pairs toward Pt clusters dominates the dynamics of charge transfer. This study shows the potential of directly using halide perovskites for light-driven reactions in polar environments.

Probing the energy transfer process by controlling the morphology of CH3NH3PbBr3 nanocrystals with rhodamine B dye

AuNP Plasmon-boosted MAPbBr3 perovskite nanocrystals for enhanced photoelectrochemical hydrogen evolution reaction