Metal halide perovskites (MHPs) are promising emitting materials for next-generation light-emitting diodes (LEDs) because MHPs have the advantages of easy solution processing, high color purity with a narrow full width at half maximum, easy synthesis and color tunability, and inexpensive material cost. Compared to the low dimensional 0D nanoparticles or 2D Ruddlesden-Popper MHPs, polycrystalline MHPs have fundamental electroluminescent (EL) limitations in terms of low exciton binding energy, long exciton diffusion length, and severe exciton quenching routes at the interface between conducting oxide anode and MHP emitting layer and in the MHP bulk. Here, we present the efficient strategies of the fine stoichiometry method, a self-organized conducting polymeric anode, nanograin engineering, and core-shell-mimicked polycrystal to achieve highly efficient polycrystalline MHP LEDs (PeLEDs). First, we suggest the highly efficient polycrystalline MAPbBr₃ PeLEDs by controlling the precursor stoichiometry, improving surface morphology, and decreasing the grain size of the MAPbBr₃ film. As a result, the current efficiency was improved from 0.002 cd/A to 42.9 cd/A. By unraveling the additive-based nanocrystal pinning (A-NCP) method, the limitations of EL efficiency in MHP films and PeLEDs were investigated so as to achieve an external quantum efficiency of 8.79% ph el^-1. By adopting these strategies to the flexible graphene, we developed graphene-based MAPbBr₃ PeLEDs that is beneficial to the out-coupling effect and exciton quenching due to In and Sn ions from ITO electrode. Then, we investigated a molecularly-decoupled ideal conducting polymeric anode for high-efficiency PeLEDs. Conducting polymers have a trade-off between a conductivity and a work function; i.e., the work function of conducting polymers decreases when the conductivity increases. Therefore, we introduce an effective molecular scale control strategy to decouple the work function with conductivity in conducting polymer anodes while maintaining the blocking capability of exciton quenching. Thereby, the high device efficiencies of 52.86 cd A^-1 and 10.93% ph el^-1 were achieved in MAPbBr₃ PeLEDs. In addition, we developed kinetically-controlled core-shell-mimicked nanograins by incorporating a molecular semiconducting additive to shield the nanograins for suppressing defects at grain boundary region. The organic-shielded polycrystalline nanograins achieved improved photophysical and electroluminescence properties, and reduced free carrier density; and thus external quantum efficiency of 11.7% ph el^-1 was achieved. Our various strategies for high-efficiency polycrystalline PeLEDs will provide broad interests to the research fields of perovskite electronics.