Effects of co-addition of CuBr₂ and NaCl to CH₃NH₃PbI₃(Cl) perovskite solar cells were investigated on the photovoltaic properties and microstructures. Short-circuit current densities and conversion efficiencies were improved by the simultaneous addition of CuBr₂ and NaCl. In addition, the efficiencies of the devices were maintained even after 10 weeks. The perovskite structure changed from a tetragonal to a cubic system by the addition of Na, which resulted in the improvement in the stabilization of the perovskite crystal.