Organic-inorganic halide perovskites recently have emerged as a promising material for highly effective light emitting diodes (LEDs) and solar cells (SCs). Despite efficiencies of both perovskite SCs and LEDs are already among the best, the development of a perovskite dual functional device that is capable of working in these two regimes with high efficiencies is still challenging. Here we demonstrate that the dual functional device based on mixed halide perovskite CH3NH3PbBr2I can be switched from SC to LED with low threshold voltage V-th < 2 V by exposing to Sun at open circuit V-oc or at small bias voltage of V-pot similar to 1-2 V. Such photo-poling creates in-situ p-i-n junction via methylammonium (CH3NH3+, MA(+)) and I-/Br- ions migration to interfaces, lowering charge injection barriers, and self-balancing injection currents in perovskite LED. We show that before the photo-poling, the electroluminescence (EL) is highly unstable in LED regime, whereas after the photo-poling, stabilized EL exhibits unusual dynamics, increasing with time and poling cycle number, while V-th and injection current decrease with cycling runs. Additionally, photo-induced and current-induced halide segregation accumulates with cycling, that is found beneficial for LED, increasing its efficiency and brightness, but reversibly degrading photovoltaic performance, which can be easily recovered.