Dual-functional surface passivation of MAPbBr3 nanocrystals: Mechanisms of defect and stability enhancement

Organic-inorganic hybrid perovskite nanocrystals (NCs) exhibit outstanding optoelectronic properties, including high photoluminescence quantum yield, tunable bandgap, and high color purity. They hold immense application potential in next-generation optoelectronic fields such as light-emitting diodes, photodetectors, and solar cells. However, their inherent instability and susceptibility to ion migration severely hinder practical implementation. Surface passivation, a key strategy for enhancing perovskite nanocrystal stability, faces the challenge of resisting water molecule intrusion. This work proposes a passivation strategy based on the bifunctional ligand 3-mercaptoacetic acid (MPA). Mediated by MPA, a non-lead metal salt, Zn(CH 3 COO) 2 , forms a passivation layer on the surface of MAPbBr 3 nanocrystals.Density functional theory (DFT) calculations at the Perdew–Burke–Ernzerhof (PBE) level elucidate this dual-functional mechanism at the molecular level. Molecular electrostatic potential analysis reveals that the sulfur atom in MPA's thiol group (-SH) acts as a nucleophilic center, strongly bonding with Pb 2 + to eliminate surface halide vacancies and passivate interface defects, which is supported by a high adsorption energy of −2.21 eV. Simultaneously, the oxygen atoms in its carboxyl group (-COOH), carrying a strong negative charge, effectively chelate Zn 2+ . This interaction exhibits a lower adsorption energy (−0.037 eV), which helps to lower the deposition barrier and guides the uniform, conformal coverage of Zn(CH 3 COO) 2 over the perovskite surface. This interfacial chemical design achieves near-defect-free interface bonding while constructing a dense hydrophobic barrier to address perovskite's water sensitivity—passivated modified nanocrystals maintained over 60 % of their initial photoluminescence intensity after 6 days of pure water immersion, significantly outperforming unmodified pristine nanocrystals. When applied as color conversion and light-absorbing layers in optoelectronic devices: the white light-emitting diode (WLED) achieved 130.6 % NTSC and 97.5 % Rec. 2020 wide color gamut output; the planar solar cell attained 15.1 % power conversion efficiency, a 2.3 % improvement over unmodified devices; The photocurrent response of the ultraviolet detector increased from 9.89 μA/cm² to 11.89 μA/cm², with the light-to-dark current ratio rising from 23 to 61.29. This study provides an innovative approach to ligand engineering for designing high-performance, highly stable perovskite nanomaterials and deepens the understanding of interfacial passivation mechanisms.