Electroluminescence and stability measurements. (a) Capacitance versus frequency spectra of Cs5Pb and Cs5Pb.0.05GuaI based devices under short-circuit condition in the frequency range from 200 MHz to 1 MHz. The active area of perovskite solar cell is 0.16 cm2 for both measurements. (b) External electroluminescence quantum efficiency as a function of the injection current for the Cs5Pb and Cs5Pb.0.05GuaI devices. (c) A comparison of operational stability of Cs5Pb and Cs5Pb.0.05GuaI devices. The devices were measured under a nitrogen environment at room temperature under constant illumination (LED source, approximated 1 Sun) at a maximum power point for 200 h.