  Perovskite light-emitting diodes (PeLEDs) have drawn considerable attention
for their favorable optoelectronic properties. Perovskite light-emitting
electrochemical cells (PeLECs) _ devices that utilize mobile ions _ have
recently been reported but have yet to reach the performance of the best
PeLEDs. We leveraged a poly(ethylene oxide) electrolyte and lithium dopant in
CsPbBr3 thin films to produce PeLECs of improved brightness and efficiency. In
particular, we found that a single layer PeLEC from CsPbBr3:PEO:LiPF6 with 0.5%
wt. LiPF6 produced highly efficient (22 cd/A) and bright (~15000 cd/m2)
electroluminescence. To understand this improved performance among PeLECs, we
characterized these perovskite thin films with photoluminescence (PL)
spectroscopy, scanning electron microscopy (SEM), atomic force microscopy
(AFM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD).
These studies revealed that this optimal LiPF6 concentration improves
electrical double layer formation, reduces the occurrence of voids, charge
traps, and pinholes, and increases grain size and packing density.
