Strain-decoupled core/shell perovskite nanocrystals for high-efficiency light-emitting diodes

Abstract

Metal halide perovskite (MHP) nanocrystals (NCs) have excellent optoelectronic properties but suffer from strain-induced lattice instability and defect formation. We present a dual-strain-decoupling strategy that independently modulates internal and surface strains in MHP NCs for use in light-emitting diodes (LEDs). Internal strain is relieved using systematic multi-cation alloying, which stabilizes the lattice, suppresses defect formation, and increases radiative recombination. However, this alloying induces residual surface strain due to mismatch between the alloyed core and undercoordinated surface. To address this problem, we introduce a bifunctional pseudohalide that passivates surface halide vacancies while selectively relaxing surface strain without perturbing the core. This dual approach reduces total microstrain in MHP, decreases trap density, and increases photoluminescence quantum yield to as much as 95%. The resulting LEDs achieve an external quantum efficiency of 30.6% and a current efficiency of 119.8 cd A-1. This work establishes strain-field decoupling as a key design principle for high-efficiency perovskite emitters, and offers a generalizable method for synthesis of nanostructured optoelectronic materials.