  Perovskite light emitting devices have drawn considerable attention for their
favorable optoelectronic properties. High carrier mobilities make perovskites
excellent candidates as host materials in electroluminescent devices. To
achieve high performance in a simple single layer device, we employed a CsPbBr3
perovskite host and a novel ionic iridium complex guest along with a
polyelectrolyte to demonstrate efficient light emitting electrochemical cells
(PeLECs). For an optimal guest/host blend, 10600 cd/m2 luminance at 11.6 cd/A
and 9.04 Lm/W are achieved at 4.1 V. These devices showed voltage-dependent
electroluminescence color proceeding from orange-red to green, facilitated by
the reconfigurable ionic materials blend. Optimized devices exhibited stable
operation under constant current driving, maintaining >630 cd/m2 emission for
40 h. Our rationally-designed ionic guest at an optimal concentration of the
host produced efficient (>90%) Forster energy transfer and improved thin film
morphological for high performance PeLEC operation enabled by ionic migration
to interfaces
