Quantum　dot　(QD)　light-emitting　diodes　(QLEDs)　have　become　one　of　the　primary　development　directions　for　next-generation　display　techniques　due　to　their　excellent　optoelectronic　and　solution-processing　properties.　High-performance　QLEDs　rely　on　high-quality　light-emitting　layers　that　are　mainly　stacked　QD　films　deposited　by　spin-coating　(SC).　However,　preparing　large-area　and　defect-free　monolayer　films,　which　is　crucial　for　high-quality　displays,　is　the　inherent　drawback　of　the　SC　technique　and　is　still　challenging.　Herein,　we　propose　an　in-situ　defect-repairing　strategy　to　create　defect-passivating　monolayer　QD　films　at　a　liquid/air　interface　by　a　simple　injection　assembly　(IA)　technique.　The　monolayer　QD　film　was　assembled　and　passivated　by　a　simple　n-butyl-amine　injection　into　ethylene　glycol　(EG),　prompting　the　IA-QLEDs　to　exhibit　excellent　electrical　performance.　The　as-fabricated　IA-QLEDs　outperform　conventional　SC-QLEDs　with　EQEs　exceeding　24　%　and　significantly　extended　lifetimes.　Furthermore,　our　method　demonstrated　its　scalability　(a　defect-free　7x5　cm2　monolayer　is　fabricated),　enabling　the　fabrication　of　large-area　QD　films　with　uniform　morphology　through　a　straightforward　expansion　of　the　film-forming　container.　This　work　proposes　a　general　strategy　for　interfacial　film　formation　and　defect　repair　of　QD　film　and　holds　significant　promise　for　the　practical　application　of　high-performance　QLEDs.