  Hybrid perovskites are emerging as highly efficient materials for
optoelectronic applications, however, the operational lifetime has remained a
limiting factor for the continued progress of perovskite light emitting devices
such as light emitting diodes (LEDs) and perovskite light emitting
electrochemical cells (PeLECs). In this work, PeLECs utilizing an optimized
fraction of LiPF6 salt additive exhibit enhanced stability. At 0.5 wt% LiPF6,
devices exhibit 100 h operation at high brightness in excess of 800 cd/m2 under
constant current driving, achieving a maximum luminance of 3260 cd/m2 and power
efficiency of 9.1 Lm/W. This performance extrapolates to a 6700 h luminance
half-life from 100 cd/m2, a 5.6-fold improvement over devices with no lithium
salt additive. Analysis under constant voltage driving reveals three current
regimes, with lithium addition strongly enhancing current in the second and
third regimes. The third regime correlates degradation of luminance with
decreased current. These losses are mitigated by LiPF6 addition, an effect
postulated to arise from preservation of perovskite structure. To further
understand lithium salt addition, electrochemical impedance spectroscopy with
equivalent circuit modeling is performed. Electrical double layer widths from
ionic redistribution are minimized at 0.5wt% LiPF6 and inversely correlate with
efficient performance.
