Mechanistic Insight into Surface Defect Control in Perovskite Nanocrystals: Ligands Terminate the Valence Transition from Pb²⁺ to Metallic Pb⁰

Abstract

Organolead halide perovskite nanocrystals (NCs) have emerged as promising materials for various optoelectronic applications. However, their practical applications have been limited due to low structural integrity and poor luminescence stability associated with fast attachment−detachment dynamics of surface capping molecules during postprocessing. At present, a framework for understanding how the functional additives interact with surface moieties of organolead halide perovskites is not available. Methylammonium lead bromide NCs without surfactants on their surface provide an ideal system to investigate the direct interactions of the perovskite with functional molecules. When the oleic acid is used in a combination with n-octylamine, its contribution to surface passivation is significantly increased by protonating the alkyl amine to the corresponding ammonium ion. Our results demonstrate that the Br vacancies at the nonpassivated surface result in a reduction of Pb 2+ to Pb 0 by trapping electrons generated from the exciton dissociation, which provides a main pathway for exciton trapping.

X-ray stability and degradation mechanism of lead halide perovskites and lead halides

“…This involves the excitation of an electron from the halide dominated valence band edge to the lead dominated conduction band edge 2 and therefore a transfer of electron density from the halide to Pb. The reaction has been shown to be catalysed by the high defect (trap) density 45,46 in the perovskite. This could explain why the reaction only starts after a certain fluence, specifically after 10 19 photons/cm 2 , as the reaction requires the build-up of defects in the film.…”

In-plane stimulated emission of polycrystalline CH3NH3PbBr3 perovskite thin films

“…S3c and d †), as more boundary leads to more defects in crystallization. 29,30 It seems that smaller grains will reduce the in-plane SE. For other perovskite lms, which contain only submicron crystal grains, no obvious in-plane SE can be found at these edges.…”

Solubility‐Controlled Room‐Temperature Synthesis of Cesium Lead Halide Perovskite Nanocrystals

“…[13][14][15] Furthermore, the formation of nanoscale metallic Pb NCs can be promoted at higher temperature (120~150°C) prior to the addition of CsOL in the typical hot-injection method, which create non-radiative pathways of the charge carriers. [16,17] Alternative routes to overcome these limitations were reported such as the solvothermal, [18] ultrasonication, [19] and ligand-assisted reprecipitation (LARP) method. [20,21] In particular, the LARP technique has been widely used to synthesize the organic-inorganic hybrid lead halide perovskites NCs, [9,10,17,22] which does not require heating and inert atmosphere.…”

“…[16,17] Alternative routes to overcome these limitations were reported such as the solvothermal, [18] ultrasonication, [19] and ligand-assisted reprecipitation (LARP) method. [20,21] In particular, the LARP technique has been widely used to synthesize the organic-inorganic hybrid lead halide perovskites NCs, [9,10,17,22] which does not require heating and inert atmosphere. [20,21] The recrystallization of the precursors (dissolved in a good solvent) can be induced by their supersaturation in a poor solvent (e. g. toluene), resulting in the formation of colloidal NCs in the presence of ligands (mainly carboxylic acids and primary amines).…”

“…Although great success to control their chemical composition, size, and morphology have been achieved in hot‐injection method, more practical approach for scalable synthesis with a higher reaction or production yield still remains a challenge due to an inhomogeneous nucleation arising from a drop in the temperature by the injection of large quantities of the precursor solution [13–15] . Furthermore, the formation of nanoscale metallic Pb NCs can be promoted at higher temperature (120∼150 °C) prior to the addition of CsOL in the typical hot‐injection method, which create non‐radiative pathways of the charge carriers [16,17] …”