Manipulating crystallization dynamics through chelating molecules for bright perovskite emitters

Abstract

Molecular additives are widely utilized to minimize non-radiative recombination in metal halide perovskite emitters due to their passivation effects from chemical bonds with ionic defects. However, a general and puzzling observation that can hardly be rationalized by passivation alone is that most of the molecular additives enabling high-efficiency perovskite light-emitting diodes (PeLEDs) are chelating (multidentate) molecules, while their respective monodentate counterparts receive limited attention. Here, we reveal the largely ignored yet critical role of the chelate effect on governing crystallization dynamics of perovskite emitters and mitigating trap-mediated non-radiative losses. Specifically, we discover that the chelate effect enhances lead-additive coordination affinity, enabling the formation of thermodynamically stable intermediate phases and inhibiting halide coordination-driven perovskite nucleation. The retarded perovskite nucleation and crystal growth are key to high crystal quality and thus efficient electroluminescence. Our work elucidates the full effects of molecular additives on PeLEDs by uncovering the chelate effect as an important feature within perovskite crystallization. As such, we open new prospects for the rationalized screening of highly effective molecular additives.

Deep‐Red Perovskite Light‐Emitting Diodes Based on One‐Step‐Formed γ‐CsPbI3 Cuboid Crystallites

“…[41] Recently, works from Zhu et al and Zou et al also reported that the interaction between additive and FAI/PbI 2 will form stable intermediate and retard perovskite nucleation, yielding high-quality crystallites with reduced trap densities. [42,43] These conclusions agree well with our experimental results.…”

Sulfonic Zwitterion for Passivating Deep and Shallow Level Defects in Perovskite Light‐Emitting Diodes

“…This intermediate structure can restrain the chemical interaction of among precursor components, leading to retarding crystallization and enhancing crystallinity with vertical orientation. [6,28] Meanwhile, this slow crystallization is beneficial to form high crystallinity perovskites, as confirmed by the Figure S1 (Supporting Information) and consistent with previous investigations. [6,28] The cross-sectional high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and energy-dispersive X-ray spectroscopy (EDS) mapping measurement suggest that these bulky grains are composite aggregates of perovskite nano-crystallites and APS molecule (Figure S4, Supporting Information).…”

“…Moreover, scanning electron microscope (SEM) images show that the FAPbI 3 film without additive is composed of random shape grains (Figure 1c), [14] while somehow cubic shape perovskite grains is formed with APS additive (Figure 1d and Figure S3, Supporting Information), which is consistent with previous study. [6,28] The change of the crystallinity by APS additive is due to the amino group in zwitterion which can form an intermediate structure with FAI and PbI 2 in the precursor solution. This intermediate structure can restrain the chemical interaction of among precursor components, leading to retarding crystallization and enhancing crystallinity with vertical orientation.…”

Reciprocally Photovoltaic Light‐Emitting Diode Based on Dispersive Perovskite Nanocrystal

“…As shown in Figure A, we found that compared with 5AVA powder, the CO bond (1000–1200 cm −1 ) and the NH bond (3117 cm −1 ) of ZnO/5AVA film moved to high wavenumber, which is the result of the interaction between 5AVA and Zn ions. [ 20 ] Moreover, the X‐ray photoelectron spectroscopy (XPS) test of 5AVA powder and ZnO/5AVA films also showed the same conclusion (Figure S22, Supporting Information). Compared with the binding energy of O 1s at 530.7 and 531.6 eV in 5AVA powder, the binding energy of O 1s in ZnO/5AVA film is 531.0 and 532.5 eV, which shifts to higher energy levels.…”

“…After 3 days, the perovskite gradually decomposed, and the peak of PbI 2 could be seen in XRD. [ 20 ] This is because the perovskite film decomposed into PbI 2 due to instability, and the instability of the perovskite film also directly leads to the decline of the stability of the device.…”