Mechanism of surface passivation of methylammonium lead tribromide single crystals by benzylamine

Abstract

Hybrid organic-inorganic perovskites are semiconductors that have great potential for optoelectronic applications such as light-emitting diodes, photodetectors, and solar cells. In such devices, the surface plays a crucial role in the performance and stability, as it strongly influences the recombination rate of excited charge carriers. It is reported that molecular ligands such as benzylamine are capable of reducing the surface trap state density in thin films. In this work, we aim to clarify the mechanisms that govern the surface passivation of hybrid perovskites by benzylamine. We developed a versatile approach to investigate the influence of benzylamine passivation on the well-defined surface of freshly cleaved hybrid perovskite crystals. We show that benzylamine permanently passivates surface trap states in these single crystals, resulting in enhanced photoluminescence and charge carrier lifetimes. Additionally, we show that exposure to benzylamine leads to the replacement of the methylammonium cations by benzylammonium, thereby creating a thermodynamically more stable two-dimensional (2D) perovskite (BA) 2 PbBr 4 on the surface of the three-dimensional crystal. This conversion to a 2D perovskite drives an anisotropic etching of the crystal surface, with the {100} planes being most prone to etching. Initially, square etching pits appear spread over the surface. As time elapses, these etching pits broaden and merge to yield large flat terraces that are oriented normally to the cleaving plane when they form. A thorough understanding of the mechanisms governing the surface passivation is crucially important to optimize and design novel passivation schemes, with the ultimate goal of further advancing the efficiency of optoelectronic devices based on hybrid perovskites.

Proton-transfer-induced 3D/2D hybrid perovskites suppress ion migration and reduce luminance overshoot

“…methylammonium halide (MAX) and lead halide (PbX 2 )) have been dissolved together in a solvent or a mixed solvent 8,[14][15][16][17][18][19] . Here, unlike the conventional way, we incorporate a liquid-form neutral reagent, benzylamine (BnA) into the methylammonium lead bromide (MAPbBr 3 ) precursor to form 3D/2D hybrid perovskites 20 . Therefore, the synthetic procedure which requires strong hydrohalic acid reagents to obtain the organic ammonium halide salt for 2D perovskites becomes unnecessary.…”

Effects of organic ligands on efficiency and stability of perovskite light-emitting diodes

“…One general strategy to improve the efficiency and operational lifetime of PeLEDs is incorporating various bulky ammonium cations, which could form Ruddlesden-Popper phases (quasi-2D phases) to suppress ion migration, and passivate the surface defect sites of perovskite grains [35][36][37]. The alkylamines, e.g.…”

On the performance of polymer-inorganic perovskite oxide composite light-emitting diodes: The effect of perovskite SrTiO3 additives

“…6 One of the potential inorganic materials that could be blended with polymer materials is perovskite. Perovskite-structured materials have been extensively studied due to their extraordinary optoelectronic characteristics, such as synthetic bandgap tunability, high absorption coefficient, good photoconductivity, and long charge carrier diffusion length with higher lifetimes, [7][8][9] making perovskite materials great for diverse applications, including light-emitting diode (LED), [10][11][12] solar cells, [13][14][15][16] photocatalysis, 17 lasers, 18 and photodetectors. 19 According to recent research, the use of lead (Pb) halide perovskite structured materials in LED devices has been reported to deliver better LED performance.…”